Phy Notes Manhatten

8/14/2019 Phy Notes Manhatten

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Chapter 1Chapter 1Light and ReflectionLight and Reflection

by Mirrorsby Mirrors1.11.1 LightLight

1.21.2 Reflection of LightReflection of Light1.31.3 Curved MirrorsCurved Mirrors


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Section 1.1Section 1.1

LightLight

Properties of light Luminous and non-luminous

objects Light rays and light beams


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Why is there an image?Reason: Light travels in straight lines

When light is blocked by an objectforms an object-liked shadow

Properties of light1.1 Light (SB p.3)


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Why can light heat up an object and

power a solar calculator?

Reason:Light is a form of energy

Properties of light1.1 Light (SB p.4)


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Why can we see objects around us?

Reason: Light from these objects enters our eyes

Objectsemit light by themselves

cannot emit light

luminous

non-luminous

Luminous and non-luminous objects1.1 Light (SB p.4)


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Which of the following is/are luminous object(s)?


emit light by themselvesObjects

cannot emit light

luminous

non-luminous


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Which of the following is non-luminous object?Why can we see non-luminous objects?

Reason:

They reflect light fromother luminous sources


emit light by themselvesObjects

cannot emit light

luminous

non-luminous


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Light ray path for the propagationof light

One light ray Three light rays

Light rays and light beams1.1 Light (SB p.5)


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Light rays

divergent parallel convergent




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Light rays and light beams1.1 Light (SB p.5)Light rays


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Light rays




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Light beam collection of light rays



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Look at an object light rays from the

object enter our eyes

only draw two lightrays to the eye

Diagrammatic representation illustrate the size:

draw two light raysfrom the tip and thefoot of the object tothe eye



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diverging rays

parallel rays

From a near object

From a very far object

from near object

from very far object



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Reflection of LightReflection of Light

Laws of reflection Formation of image by plane

mirror Applications of plane mirrors


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Reflection when a light ray strikes a surface, it is reflected from the surface

incident ray reflected ray

1.2 Reflection of light (SB p.6)


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Incident ray incoming light ray on the mirror Reflected ray light ray reflected from the

mirror




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Normal an imaginary line perpendicular to the surface at which the lightray strikes

Incidentpoint

incident ray normal reflected ray



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Angle of incidence (i) angle between the incident ray and the normal

Angle of reflection (r ) angle between the reflectedray and the normal

incident ray normal reflected ray

i r



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Laws of reflection:(i) Angle of reflection ( r ) = Angle of incidence ( i )

(ii) The incident ray , the reflected ray and thenormal all lie in the same plane

incident ray normalreflected ray

Laws of reflection1.2 Reflection of light (SB p.8)


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When parallel light rays are incident on a

smooth surface rough surface regular reflection reflected rays are parallel sharp and clear image



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diffuse reflection reflected rays are not parallel

blurred image

smooth surface rough surface regular reflection


f b l


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Plane mirror plane glass, coated with a thin layer of metal regular reflection takes place

(form clear images)

glassthin layer of metalcoating

Formation of image by plane mirror 1.2 Reflection of light (SB p.10)

F i f i b l i


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Experiment 1B:Experiment 1B: Formation of image by a plane mirror

Expt. VCD


F i f i b l ifl f l h ( )


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When the reflected rays are extendedbackwards,

image of thelight bulb

they meet at a point (position of the image ( I ))


lightbulb

F i f i b l i1 2 R fl i f li h (SB 11)


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Distance between the object and the mirror = Distance between the image and the mirror


Object distance ( u ) = Image distance ( v )

lightbulb

F ti f i b l i1 2 R fl i f li h (SB 12)


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Construction rules for images formed byplane mirror 1. Draw an arrow

(object)2. Draw the reflected

rays from the tip of the arrow (laws of reflection)

3. Extend the reflectedrays backwards

4. Draw the reflectedrays from the foot of the arrow

5. Draw a dotted arrow(image)

object image



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Formation of image b plane mirror1 2 R fl ti f li ht (SB 13)


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pq

r s

object

Class Practice 1Class Practice 1 An object ( O), represented by anarrow, is placed in front of a plane mirror. Four rays, p, q, r and

s are drawn from the object to the mirror as shown in thefollowing figure. Draw the reflected rays and locate the image( I ).

Answer

image


Formation of image by plane mirror1 2 R fl ti f light (SB 14)


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Class Practice 2Class Practice 2 : A clock is placed in front of a planemirror. What is the time shown in the clock?

10:10

Answer


Applications of plane mirrors1 2 Reflection of light (SB p 15)


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Applications of plane mirrors

The wordsare laterallyinverted

1. Rear-view mirror see the traffic behind images are laterally inverted

Applications of plane mirrors1.2 Reflection of light (SB p.15)



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2. Periscope see things over an obstacle

ray fromfar object




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3. Dressing mirror

used inwashrooms andfitting rooms

4. Interior decoration

make a place lookspacious



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Section 1.3Section 1.3 Curved MirrorsCurved Mirrors

Terminology for curved mirrors Construction rules for images formed by

curved mirrors Formation of images by curved mirrors Magnification Image nature of curved mirrors

Finding the focal length of a concave mirror Applications of concave mirrors Applications of convex mirrors

1 3 Curved mirrors (SB p 19)


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Curvedmirrors

concave mirrors

convex mirrors

reflecting surfacecurves inwards

convexmirror

reflecting surfacecurves outwards

concavemirror

reflectingsurface

reflecting

surface

1.3 Curved mirrors (SB p.19)



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Curved

mirrors

cylindricalmirrors

sphericalmirrors

cylindricalconcave mirror

cylindricalconvex mirror





1.3 Curved mirrors (SB p.19)inner reflectingsurface of acylinder

outer reflectingsurface of acylinder



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Curved

mirrors

cylindricalmirrors

sphericalmirrors

sphericalconcave

mirror

sphericalconvexmirror

sphericalconvex mirror

sphericalconcavemirror


spherical concavemirror

spherical convexmirror

inner reflecting surface

of a sphere

outer reflecting surfaceof a sphere



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concave mirror

convex mirror

reflected rays converge

reflected rays diverge

convergingmirror

divergingmirror


concave mirror convex mirror

Terminology for curved mirrors1 3 Curved mirrors (SB p 20)


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1. pole ( P )

3. radius of curvature ( r )4. principal axis

2. centre of curvature ( C )

1. pole ( P )2. centre of curvature ( C )

3. radius of

curvature ( r )

Terminology for curved mirrorsconcavemirror

convexmirror

Terminology for curved mirrors1.3 Curved mirrors (SB p.20)

4. principal axis

Terminology for curved mirrors1 3 Curved mirrors (SB p 21)


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Experiment 1C:Experiment 1C: Reflection of light by

concave and convex mirrorsExpt. VCD




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focus ( F )

When parallel light rays are incident on a concave mirror convex mirror

reflected light rays converge to a point principal focus

or focus ( F )

principalaxis




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focus ( F )

When parallel light rays are incident on a concave mirror

convex mirror reflected rays converge to a point

focus ( F )

e o ogy o cu ved o s1.3 Curved mirrors (SB p.22)

reflected rays diverge , when theyextended backwards, they meet ata point



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Focal plane

Focal length ( f )

cuts F , perpendicular to theprincipal axis

distance between F and P = r 1

2

focalplanefocalplane

gy1.3 Curved mirrors (SB p.22)

Construction rules for images1.3 Curved mirrors (SB p.22)


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Graphical symbols

concave mirror convex mirror

formed by curved mirrors( p )

Construction rules for images formed1.3 Curved mirrors (SB p.23)


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1. Parallel to theprincipal axis

Construction rules for images formed byconcave mirrors

pass through F

by curved mirrors( p )



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2. Towards F parallel to theprincipal axis





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3. Towards C reflected along thesame path as theincident ray





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4. Strikes the pole atan angle

r = i

ir





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Ray 2 is the reverse of ray 1Principal of reversibility of light

light ray will retraceits original path

Reason: Principal of reversibility of light

ray 1

ray 2

If a light ray isreversed in direction




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passes through F after extendedbackwards

by curved mirrors

Construction rules for images formed byconvex mirrors



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by curved mirrors




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3. Towards C reflected alongthe same path asthe incident ray

by curved mirrors




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4. Strikes the pole atan angle

r = i

ir

by curved mirrors


Formation of images by curved mirrors1.3 Curved mirrors (SB p.25)


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Experiment 1D:Experiment 1D: Formation of image by

concave and convex mirrorsExpt. VCD



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Locate the images formed byconcave mirror using graphical method

1. Draw an arrow (object)2. Draw two special light

rays from the tip of theobject

3. Draw the reflectedrays to meet at apoint

4. Draw an arrow (image)

Nature of images formed by a concave mirror changes with the position of the object



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1. Draw an arrow (object)2. Draw two special light

rays from the tip of theobject

3. Extend the reflectedrays backwards andintersect at a point

4. Draw a dotted line

arrow (image)Nature of images formed bya convex mirror inverted, virtual and diminished

Note: Virtual images cannot be formed on thescreen, you observe them by looking into the mirrors

directly.

Locate the images formed byconvex mirror using graphical method

Magnification1.3 Curved mirrors (SB p.27)


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Magnification ( m ) =Height of image ( h i)

Height of object ( h o)

= Image distance ( v )Object distance ( u )

u

v

similar

triangles

ho

hi

m (plane mirror) = 1

concave mirror

principalaxis



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Class Practice 3Class Practice 3 (a)(a) An object ( O) is placed at 20 cm in front of a concave

mirror of focal length 40 cm as shown in the followingfigure. Draw two light rays to locate the image ( I ). Use ascale of 1 cm to represent 10 cm in the horizontal axis.

Answer

I



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Class Practice 3 (Contd)Class Practice 3 ( Contd) (b)(b) Find the image distance. Hence, find the magnification.

Image distance = ______________

Magnification =

=

=

) () (

) () ( Ans

wer

4 10 = 40 cm

Image distance

Object distance40

20

2



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Class Practice 4Class Practice 4

(a)(a) The positions of an object and its image formed by aconvex mirror are shown in the following figure.Locate the principal focus ( F ) of the mirror in thefigure.

Answer



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Class Practice 4 (Contd)Class Practice 4 ( Contd)

(b)(b) Find the focal length and magnification of the mirror. Use a scale of 1 cmto represent 2 cm in the horizontal axis.

Focal length of the mirror =

Magnification =

=

=

) () (

) () (

Answer

4 2 = 8 cm

Image distance

Object distance

2 2

4 2

0.5

Image nature of curved mirrors1.3 Curved mirrors (SB p.31)


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1. Object is placed

between P and F Image is formed

behind the mirror Nature of image virtual erect laterally inverted

magnified(m > 1)

Nature of image formed by a concave mirror

object

image



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2. Object is placed at F

Image isformed at

infinity Nature of

image

cannot bedetermined

object



f f d b


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3. Object is placedbetween F and C

Image is formedbeyond C

Nature of image real inverted magnified

(m > 1)

objectimage



N f i f d b i


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4. Object is placed at C

Image is formedat C

Nature of image real inverted

same size asthe object(m = 1)

object image



N f i f d b i


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5. Object is placed beyondC

Image is formedbetween C and F


diminished(m < 1)

object image



N f i f d b i


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6. Object is placed at

infinity Image is formedon the focal plane

Nature of image real inverted diminished

(m < 1)

image




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Class Practice 5Class Practice 5 : The figureshows the image formed when a toy

is placed in front of a concave mirror.

Answer

(b)(b) State the approximate position of the toy being placed.

The toy is placed .

The image is virtual, erectand magnified.

between F and the mirror

(a)(a) State the nature of the image.



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Note: When the object isplaced at infinity , the image isformed on the focal plane.

Image is formedbetween F and P

Nature of image

virtual erect diminished

(m < 1) laterally

inverted

object

image

Nature of image formed by a convex mirror Object is placed at any position



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Class Practice 6Class Practice 6 : A toy is placed in front of a convexmirror at two different object distances. The images formed

are as follows:

case 1 case 2



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Answer

Class Practice 6 (Contd)Class Practice 6 ( Contd) Use a ray diagram to account for the difference in image size.

The image size in case 1 is than that in case 2 because.

the toy is placed nearer to the mirror

larger

E i t 1EExperiment 1E:Finding the focal length of a concave mirror 1.3 Curved mirrors (SB p.35)


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Experiment 1E:Experiment 1E: Finding the focal length of a concave mirror

Expt. VCD

Object at infinitFinding the focal length of a concave mirror 1.3 Curved mirrors (SB p.35)


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Image distance = Focal length of the concave mirror

Object at infinityconcave mirror converges the parallel rays on

the focal plane

principalaxis

focallength ( f )focal

plane

parallellight rays

Al i h d fi d h f l l hFinding the focal length of a concave mirror 1.3 Curved mirrors (SB p.36)


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Alternative method to find the focal lengthof a concave mirror

Object at C of a concave mirror Size of image = Size of object Image distance = Object distance = r

r

2f =r

object image

Applications of concave mirrors1.3 Curved mirrors (SB p.37)


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1. Shaving and make-

up mirrorsFaces within F of themirror magnified anderect image

2. Solar furnace

Sunlight converges to thefocus high light intensity andtemperature at the focus

Applications of concave mirrors

fl



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3. Reflector

Car headlamp

Torches Concave mirror used in surgery

D o y o u k n o w

r e f l e c t o r s

a r e n o t s p h e r

i c a l i n s h a

p e ?

Light source at the focus of the concave mirror

reflected beams are parallel



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Not all reflected rayscan converge to thefocus

All reflected rayscan converge tothe focus

3. ReflectorsSpherical

concave mirror

Parabolic

concave mirror



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plane mirror

eyepiece

4. Reflecting telescope

Applications of convex mirrors1.3 Curved mirrors (SB p.40)


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provides a wider field of view

image formedis diminished

plane mirror

convex mirror

Applications of convex mirrors

Applications of convex mirrors1.3 Curved mirrors (SB p.40)


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1. Rear-view mirror see the things behind

2. Security mirror prevent shoplifting

3. Road safety

mirror see round a bend


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Manhattan Press (H.K.) Ltd. 2001

Chapter 2Chapter 2Refraction2.12.1 Refraction of LightRefraction of Light2.22.2 Laws of RefractionLaws of Refraction

2.32.3 Examples of RefractionExamples of Refraction

2.42.4 Total Internal ReflectionTotal Internal Reflection


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Refraction of LightRefraction of Light

Refraction when light ray travels from one2.1 Refraction of light (SB p.53)


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Refraction when light ray travels from onemedium to another medium

travelling direction of the light ray changes

incident

ray

refractedray

emerging

ray

Note:Light ray can travelin different media(e.g. air, water andglass).

air

glass

Wh d h li h f i2.1 Refraction of light (SB p.53)


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85

Where does the light ray refract inthe glass?

Refraction 1:from air to glass

Refraction 2from glass to air

air glass

air


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Laws of RefractionLaws of Refraction

Refractive index

Wh li ht t l f i t l2.2 Laws of refraction (SB p.54)


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When a light ray travels from air to glass ,

light rayrefracted ray (strong)

reflected ray (weak)


air

glass

interface

refractedray

N l h h i id i2.2 Laws of refraction (SB p.54)


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89

Normal pass through incident point,perpendicular to the air-glass interface

normal

Incidentpoint


air

glass

interface

refractedray

A l f i id ( i)angle between the incident

2.2 Laws of refraction (SB p.54)


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90

Angle of incidence ( i ) ray and the normal

Angle of refraction ( r ) angle between the refracted ray and the normal

i

r


air

glass

interface

refractedray

normal

E i t 2AExperiment 2A:2.2 Laws of refraction (SB p.54)


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91

Experiment 2A:Experiment 2A: Refractive index of glass

Intro. VCD

Expt. VCD

A li h l f i l bli l

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92

normal

A light ray travels from air to glass obliquelyIt bends towards the normal

original path of the light ray

G raph of sin i2.2 Laws of refraction (SB p.55)


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93

G raph of sin i against sin r

1. pass through theorigin

sin i sin r = constant2.



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94

Laws of refraction

1. The incident ray, therefracted ray and thenormal all lie in thesame plane

sin i sin r

= constant2.

Note: It is also calledSnells law.

normal

air

glass

Interface

strongrefracted ray

incidentray

weakreflected ray

When a light ray travels fromRefractive index2.2 Laws of refraction (SB p.56)


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When a light ray travels from1. air to glass

2. glass to air

refracted ray bends towards

the normalrefracted ray bends away fromthe normal(principle of reversibility of light)

air

glass

normal

air

glass

normal

Refractive index2.2 Laws of refraction (SB p.56)


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Refractive index

of glass (n

g)

When a light ray travels from air to glass

sin i sin r

Refractive index

sin

a

sin gn g =

air

glass

normal

i

r =

What is theRefractive index2.2 Laws of refraction (SB p.57)


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97

Method 1 n g = Slope of the graph

= 1.5

What is therefractive index of glass ( n g)?

Method 2

Apply the equation:n

g sin asin g

=



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98

Refractive indices of some materials

(n )1.00

1.0003 1.00

1.33

1.36

1.50

1.50 1.70

2.42

Material Refractive index ( n )

VacuumAir

Water AlcoholPerspex

Glass

Diamond

Different materials haveRefractive index2.2 Laws of refraction (SB p.57)


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Different materials havedifferent refractive indices

different angle of refraction ( r 1

r 2)

nw = 1.33 ng = 1.5

r 1

r 2

air

water

normal

glass

air

normal

n (1 33) < n (1 5)Refractive index2.2 Laws of refraction (SB p.58)


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nw (1.33) < n g (1.5)

refracted ray in glass bendstowards the normal more (r 1 > r 2)

nw = 1.33 ng = 1.5

r 1

r 2

air

water

normal

glass

air

normal

Optically denser medium a medium with greater n



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Optically denser medium

Optically less dense medium

a medium with greater n

a medium with

smaller nglass ( n g = 1.5)

water ( n w = 1.33)

optically denser mediumoptically less dense medium

nw = 1.33 ng = 1.5 air

water

normal

glass

air

normal

A light ray travels from anRefractive index2.2 Laws of refraction (SB p.58)


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optically denser medium

optically lessdense medium

normal

optically less dense medium

optically denser mediumrefracted raybends towards the normal

A light ray travels from an


A light ray travels from an


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optically lessdense medium

optically denser medium

normal

refracted ray

bends away fromthe normal

A light ray travels from anoptically denser medium

optically less dense medium

Class Practice 1Class Practice 1 : A light ray travels from air to water as



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AnswerClick for answer now!!

Class Practice 1Class Practice 1 : A light ray travels from air to water asshown in the following figure.

(a)(a) Find the angle of reflection and theangle of refraction. The refractiveindex of water ( nw) is 1.33.

Angle of reflection =_______

75o

air

water

=

=

=

6.46

sin75sin33.1

sinsin

w

w

w

aw

By Snells Law,

Class Practice 1 (Contd)Class Practice 1 (

Contd)



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air

water

(b)(b) Sketch the reflected and refracted rays in the

figure.

Class Practice 1 (Cont d)Class Practice 1 ( Cont d)


reflectedray

air

water

refractedray

Class Practice 2Class Practice 2 : A light ray travels through a glass



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Class Practice 2Class Practice 2 : A light ray travels through a glass prism as shown in the following figure. The refractive indexof the prism is 1.5. Find the angles i, a , b, c and d . Hence,find angle r .

=

=

==

==

==

=

=

==

4.52

5.1sinsin

9.311.5890

1.589.6160180

9.611.2890

1.28

5.1sin

sin

454590

r

d

r

d

c

b

aa

i

i


normal


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Examples of RefractionExamples of Refraction

Real depth and apparent depth Refraction by prism

2.3 Examples of refraction (SB p.61)


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Experiment 2B:Experiment 2B: Refraction of light

Expt. VCD

Light rays are refracted at the

Real depth and apparent depth2.3 Examples of refraction (SB p.62)
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in the absenceof water

Light rays cannot reach the eye

g ywater-air interface

light rays can reach the eye

Note: The objectappears raised.

Refracted rays extendbackwards (dotted lines)

and meet at a point(position of image)

air water

distance between the water

Real depth and apparent depth2.3 Examples of refraction (SB p.62)


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Real depth ( D )

Apparent depth ( D)

surface and the object

real depth

distance between the water surface and the image

apparentdepth

Prism triangular glass prism

Refraction by prism2.3 Examples of refraction (SB p.63)


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Prism triangular glass prism when a white light passes through it,

a spectrum of different colours isformed

spectrum

whitelight

prism

redorangeyellowgreenblue

indigo

violet

Wh i f d?



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Why is a spectrum formed?

Reason: White light consists of different coloursdifferent colours have

different refractive indices

refract at differentangles of refraction

dispersion of white light

whitelight

prism

redorangeyellowgreenblue

indigoviolet

Class Practice 3Class Practice 3 : A huntsman sees a shark in the water



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Class Practice 3Class Practice 3 : A huntsman sees a shark in the water as shown in the figure below.

Answer!Click for answer now!!

(a)(a) Locate the apparent position of the shark in the figure.

shark

apparent position of the shark

Cl P i 3 (C d)Cl P ti 3 (

C td)



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(b)(b) The shark appears to be (smaller/larger) in size, because the shark appears to be at a position

(farther away from/nearer to ) thewater surface.

Class Practice 3 (Contd)Class Practice 3 ( Contd)

larger


nearer to


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Section 2.4Section 2.4Total Internal ReflectionTotal Internal Reflection

Critical angle Examples of total internal reflection

Applications of total internalreflection


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At a small angle refracted ray (strong)2.4 Total internal reflection (SB p.65)


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gof incidence ( i )

y ( g) reflected ray (weak)

partialreflected rayincident ray

air water

normal partialrefracted

ray


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Angle of refraction r refracted ray (weak)2.4 Total internal reflection (SB p.65)


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g= 90

angle of incidence ( i ) = critical angle ( c )

y ( )

reflected ray (strong)

critical angle ( c )

i

incidentray

partialreflected ray

air

water

normal

partialrefracted ray

Angle of incidence ( i )C i i l l

no refracted ray2.4 Total internal reflection (SB p.65)


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> Critical angle reflected ray only

This phenomenon is calledtotal internal reflection

i i

incidentray

totalreflected

ray

air

water

normal

Two conditions for the occurrence of

2.4 Total internal reflection (SB p.66)


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Two conditions for the occurrence of total internal reflection

1. Light ray travels froman optically denser medium (water) to anoptically less dense medium (air)

2. Angle of incidence (i ) > Critical angle (

c ) of the optically denser

medium (water)

incidentray

totalreflected ray

air

water

normal

Experiment 2C:Experiment 2C: 2.4 Total internal reflection (SB p.66)


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Critical angle and total internal reflection

Expt. VCD

Calculate the critical angle ( c ) of glassCritical angle2.4 Total internal reflection (SB p.68)


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g ( ) g

ng

sin asin g

=

sin 90 o

sin c =

ng = 1.5 c = 42 o

By Snells Law,

air

glass

c = sin 1 ( )1n

g

Critical angles of some materialsCritical angle2.4 Total internal reflection (SB p.68)


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Critical angles of some materials

( n ) ( c )1.33 = 8.48)33.1

1(sin 1

1.50 = 8.41)

5.11(sin 1

2.42 = 4.24)42.21

(sin 1

c = sin 1 ( )1n

Material

Water

GlassDiamond

Refractive index ( n ) Critical angle ( c )

Class Practice 4Class Practice 4 : A light ray travels from water to air.

Critical angle2.4 Total internal reflection (SB p.69)


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Describe the changes in the brightness of the refracted rayand the reflected ray when the angle of incidence ( i) increasesfrom 0 to 60. The critical angle of water is 48.8.

When 0 < i < 48.8 , _____________________________.

When i = 48.8 , __________________________________.

When i > 48.8 , __________________________________.

a weak reflected ray and astrong refracted ray are

observed.

a strong reflected ray appears and aweak refracted ray emerges along

the water-air boundary.

the ligh t ray is totally reflected at thewater-air boundary and the reflectedray becomes as bright as the incident

ray. No refracted ray is observed.


Class Practice 5Class Practice 5 : Referring to the following figure,t th f ll i g t t tT l i l fl i d

Critical angle2.4 Total internal reflection (SB p.69)


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comment on the following statement:Since the angle of incidence (60) is greater than the critical

angle of glass (41.8), total internal reflection will occur.

air

glass

Is this statement correct? Explain briefly.


Total internal reflection does not occur because air is optically less dense than glass.

Total internal reflection only occurs when lighttravels from an optically denser medium to an

optically less dense one.

Examples of total internal reflection

Examples of total internal reflection2.4 Total internal reflection (SB p.70)


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1. Sparkle of diamond

Why is diamond more brilliant than glass?Light rays enter the diamond fromabove undergo total internal reflection

at the bottom emerge from the top surface

give brilliant colour

Reason: Critical angle of diamond (24 o )


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Why is there a mirage?2. Mirage

Reason: Light rays enter from cold air toExamples of total internal reflection2.4 Total internal reflection (SB p.71)


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total internalreflection

hot air (different media), then refraction

and total internal reflection (at A

) occur.eye of the observer

hot air

cold air

3. Scene under water Examples of total internal reflection2.4 Total internal reflection (SB p.72)


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Can the diver see the object behind the barrier?

Yes, because light rays undergo totalinternal reflection on the water surface

Experiment 2D:Experiment 2D: Applications of total internal reflection2.4 Total internal reflection (SB p.72)


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Construction of a prismatic periscope

Expt. VCD


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Class Practice 6Class Practice 6 : Is the image formed by a periscope

Applications of total internal reflection2.4 Total internal reflection (SB p.74)


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real or virtual? Complete the following ray diagram andanswer the question.

The image formed by a periscope is .virtual

object


image

object


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3. Optical fibres for telecommunicationApplications of total internal reflection2.4 Total internal reflection (SB p.76)


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total internalreflection

p light ray undergoes total internal reflection

at the core-cladding interface

light ray a light ray emerges at theopposite end of the optical fibre

core

cladding

Reasons for using optical fibres instead of bl



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copper cables

thinner, lighter and cheaper provide a higher bandwidth

and carry more telephonecalls at a time

avoid electrical interferenceand more secured

loss of signals is minimized

4. Optical fibres for endoscoped i i h i l



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doctors use it to examine the internal

organs of patients

endoscope

light illuminatesthe internal organs

of the body

light is reflected back tothe detector and is

analysed by doctors

5. Fish-eye viewli h f h f b l d



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48.8 48.8

light rays from the water surface below undergototal internal reflection on the water surface

View of fish-eye is restrictedwithin an angle of 97.6


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Chapter 3Chapter 3Lenses

3.13.1 Cylindrical and Spherical LensesCylindrical and Spherical Lenses

3.23.2 Construction Rules for ImagesConstruction Rules for ImagesFormed by LensesFormed by Lenses

3.33.3 Formation of Images by LensesFormation of Images by Lenses


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Section 3.1Section 3.1Cylindrical andCylindrical and

Spherical LensesSpherical Lenses Terminology for lenses


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Lconvex lenses the thickest at centre

3.1 Cylindrical and spherical lenses (SB p.89)


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Lensesconcave lenses the thinnest at centre

the thickest at centres of convex lenses

the thinnest at centres of concave lenses

3.1 Cylindrical and spherical lenses (SB p.89)

Lensesconvex lenses the thickest at centre


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cylindricalconvex lens

cylindricalconcave lens

sphericalconvex

lens

sphericalconcave lens

Lensesconcave lenses the thinnest at centre


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When parallel light rays pass through a3.1 Cylindrical and spherical lenses (SB p.89)


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convex lens

concave lens emerging rays diverge diverging lens

converging lens

Terminology for lenses

3.1 Cylindrical and spherical lenses (SB p.89) Terminology for lenses


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convex lens concave lens

gy

opticalcentre

principalaxis

1. Principal axis2. Optical centre ( C )

Experiment 3A:Experiment 3A: Refraction of light by convex and concave lenses



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Refraction of light by convex and concave lenses

Expt. VCD


149/371

convex lensWhen parallel light rays pass through a

emerging rays converge to a point



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convex lens

concave lens

focus (F )

emerging rays converge to a point

Note: Light rays can be directed towards alens from either side, so a lens has two foci.

focus

concave lens

emerging rays diverge,extended backwards tomeet a point :


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Greater curvature of lens



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2

1

(shorter focal length)Light rays converges

more ( 2 > 1)smaller curvature

greater curvature


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Graphical symbols

3.2 Construction rules for images formed by lenses (SB p.92)


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p y

convex lens concave lens

Construction rules for imagesf d b l

3.2 Construction rules for images formed by lenses (SB p.92)Construction rules for images

formed by convex lens


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F


passes through F onthe opposite side of the incident ray


formed by convex lensConstruction rules for images formed


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F


F

by convex lens


formed by convex lensConstruction rules for images formed


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3. Towards C passes throughC

without deviation

by convex lens

Principle of reversibilityf li h




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The refraction of ray 2 is the reverse of ray 1

of light

Reason: The principle of reversibility of light

ray 1 ray 2

Class Practice 1 :Class Practice 1 : Referring to the figure below, an image




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Class Practice 1 :C ass act ce : g g , g I is formed when an object is placed on the left hand side of aconvex lens. Draw two light rays to locate the position of theobject as O.

Answer


formed by concave lensConstruction rules for imagesf d b l


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F


appears to come from F on the same side of theincident ray

formed by concave lens




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F






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3. Towards C passes through C without deviation

|c


Class Practice 2Class Practice 2Draw the refracted ray in each of the following figures




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Draw the refracted ray in each of the following figures.

Answer

(a)(a)

(b)(b)

Section 3 3Section 3 3


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Formation of ImagesFormation of Imagesby Lensesby Lenses

Locate the images by graphicalmethod

Image nature of lenses Finding the focal length of a convexlens

Experiment 3B:Experiment 3B: Formation of image by

3.3 Formation of images by lenses (SB p.97)


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convex and concave lensesExpt. VCD

Locate the images formed by convexlens by graphical method

3.3 Formation of images by lenses (SB p.98) Locate the images bygraphical method


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lens by graphical method1. Draw an arrow

(object)

2. Draw two speciallight rays from the tip

of the object3. Draw the refractedrays to meet at apoint

4. Draw an arrow(image) to theprincipal axis

Note: Image nature of convex lens changes with object distance

principalaxis

convexlens

I

O

1. Draw an arrow (object)

3.3 Formation of images by lenses (SB p.98) Locate the images bygraphical methodLocate the images formed by concavelens by graphical method


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1. Draw an arrow (object)

2. Draw two special lightrays from the tip of theobject

3. Extend the refractedray backwards to meetat a point

4. Draw an arrow (image)to the principal axis

Note: nature of imagesformed by a concave lens erect, virtual anddiminished

concave lens

I

O

e s by g ap ca et od

Note: Virtual images cannot beformed on the screen, youobserve them by looking intothe mirrors directly.


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1 Object is placed between C and FImage nature of convex lens

3.3 Formation of images by lenses (SB p.99) Image nature of lenses


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o

I

1. Object is placed between C and F

Image is formedon the same sideas the object

Nature of image virtual erect

magnified(m > 1)

image

2 Object is placed at F


Image nature of convex lens


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o

2. Object is placed at F

Image isformed atinfinity

Nature of image

cannot bedetermined

3. Object is placed between F and 2 F

3.3 Formation of images by lenses (SB p.99) Image nature of lensesImage nature of convex lens


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o

I

j p

Image is formedbeyond 2 F on theopposite side of the lens


magnified(m > 1)

object

image

4. Object is placed at 2 F



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o

I

j p

Image is formed at2F on the oppositeside of the lens

Nature of image

real inverted same size as

object ( m = 1)

object

image

5. Object is placed beyond 2 F



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o Image is formedbetween F and 2 F onthe opposite side of the lens

Nature of image real inverted diminished ( m < 1)

object

image

6 Object is placed at infinity



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6. Object is placed at infinity

Image is formed onthe focal plane

Nature of image

real inverted diminished ( m < 1)

image

Class Practice 3Class Practice 3 In the following figure, sketch therefracted rays and locate the image ( I)



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refracted rays and locate the image ( I ).

Answer

I


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(b)(b) When a boy is at position (i)(i) X and then (ii)(ii) Y, what will he

Class Practice 4 (Contd):Class Practice 4 (

Contd):



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(b)(b) When a boy is at position (i)(i) X and then (ii)(ii) Y , what will he

see?

(i)(i) If the boy is at position X , he will see a letter _______.

(ii)(ii) If the boy is at position Y , he will see a

letter _______.

Answer

b

d

convexlens

translucentscreen

(c)(c) Draw a ray diagram to determine the image distanceClass Practice 4 (Contd)Class Practice 4 (

Contd)



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Ans

wer

( )( ) y g g

and magnification. Use the scale shown in the figure.

Image distance = __________ = __________.

Magnification _______.

6 x10

60cm

Height of object

Height of image

105

2

Object is placed at any

3.3 Formation of images by lenses (SB p.103) Image nature of lensesImage nature of concave lens


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o I

Image is formedbetween F and C ,andon the same side asthe object

Nature of image virtual erect

diminished ( m < 1)

position

object

image

Note: When the object is placed atinfinity, the image is formed on the

f l l

larger imageFocal length of concave lens is fixed,



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Shorter objectdistance

larger image,

but must be smaller thanthe object ( m < 1)

longer objectdistance shorter objectdistance

Class Practice 5Class Practice 5 An object O is placed in front of aconcave lens. Three light rays, p, q and r are directed towardsth l h i th f ll i g fig



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(a)(a) Sketch the refracted rays of p, q and r .(b)(b) Locate the image I .

the concave lens as shown in the following figure.

Answer

Class Practice 6Class Practice 6 The following figures show theimages formed by two lenses, L1 and L2. Name the lenses.



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L1 is a __________ lens, and L2 is a __________ lens.

convex

Answer conc

ave

lens L1 lens L2

Class Practice 7Class Practice 7 An object O, which is 15 cm inheight, is placed at 30 cm in front of a concave lens. Thefocal length of the lens is 15 cm



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Answer

(a)(a) Draw a ray diagram to locate the image I . Use thescale shown in the figure.

focal length of the lens is 15 cm.

(b)(b) State the nature of the image.

Class Practice 7(Contd):Class Practice 7(

Contd):3.3 Formation of images by lenses (SB p.105) Image nature of lenses


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The image is virtual, erect

and diminished.

Answer

Experiment 3CExperiment 3C Finding the focal length of a convex lens

3.3 Formation of images by lenses (SB p.105) Finding the focal length of a convex lens


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Expt. VCD

Convex lenses converge parallel light rays on

Finding the focal length of a convex lens3.3 Formation of images by lenses (SB p.106) Finding the focal length of a convex lens


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the focal planeImage distance = Focal length of convex lensparallel light

rays focal plane

principal axis

focallength ( f )


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Chapter 4Chapter 4


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Chapter 4Chapter 4Optical Instruments

4.14.1 Magnifying GlassMagnifying Glass4.24.2 Human EyeHuman Eye

4.34.3 CameraCamera


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Magnifying GlassMagnifying Glass

What is a magnifying glass?

4.1 Magnifying glass (SB p.114)


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It is a convex lens with a short focal length

Properties of a magnifying glass (convexlens)



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Object is placed within the focallength

Nature of image virtual, erect and

magnified

I

longer object distance

When focal length of a magnifying glass is fixed,4.1 Magnifying glass (SB p.115)


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longer object distance

larger magnification

shorter objectdistance

longer objectdistance

I

I

l

When object distance is fixed,4.1 Magnifying glass (SB p.116)


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thicker convex lens(shorter focal length)

larger magnification

shorter

focallength

longer

focallength I

I

Class Practice 1Class Practice 1 An object is placed in front of amagnifying glass at different positions as shown in the figurebelow Locate the images for the object at u u and u



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below. Locate the images for the object at u1, u2 and u3.

Answer

I 2

I 1

I 3


Contd)

I 2I1



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When the object is moved from u1 to u2, the image

becomes ______________ in size, but it is still _______________ and virtual. If the object is moved

to u3, the image will become ____________,

____________ and ____________.

Answer

I 1

I 3

larger erect

magnifiedinvertedreal


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Human eye Optical instrument inside our bodies

Structure of human eye4.2 Human eye (SB p.118)


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Focus objects, perceive depths, distinguishcolours

Structure of human eye(1) cornea image

control size

Structure of human eye4.2 Human eye (SB p.118)


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(2) pupil(3) iris(4) lens(5) ciliary muscles(6) retina(7) optic nerve

cornea

lens

ciliary muscles

pupil

iris retina

Note: Images formedon the retina are realand inverted.

opticnerve

formed on it

transmitsignalsto brain

control size

of pupil

controlthickness of lens

lightrays

Control of brightness depends on thesize of pupilIn bright environment,

i i d h i f il

Control of brightness4.2 Human eye (SB p.119)


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size of pupilreduces

iris reduces the size of pupil limit the amount of light entering the eye

In dim environment, size of pupil widens



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increase the amount of light entering the eye

size of pupilwidens

Colour of the eye colour of the iris



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Looking at a distant object

Accommodation depends on thicknessof lens

Accommodation4.2 Human eye (SB p.120)


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Looking at a distant object Ciliary muscles relax Lens becomes thinner

(longer focal length)

Note:Distance between lens and retina= Focal length of lens

Looking at a near object Ciliary muscles contract



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y

Lens becomes thicker (shorter focal length)

Accommodation See objects at different distances



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Ciliary muscles change the lens shape Focus images on the retina

light from

distant object

light from

near object

Range of visionFar point the farthest point that an eye can

see clearly (infinity)

Defects of vision4.2 Human eye (SB p.120)


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near pointfar point

Near point see clearly (infinity)the nearest point that an eye cansee clearly (25 cm)

Note: The range of visionfor a normal eye is fromabout 25 cm to infinity.

25 cminfinity

Experiment 4A:Experiment 4A: Model eye kit experiment



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Expt. VCD

Short-sightedness Cannot see distant objects clearly



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image formedin front of the

retina

light rays fromdistant object

Cause the eyeball is too long or the lens is too thick Effect image is formed in front of the retina

Note:Near point < 25 cm(short-sighted eye)

Correction of a short-sighted eye Wear spectacles with concave lenses



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Wear spectacles with concave lenses

light rays fromdistant object

concave lens

light rays appear to comefrom a nearer point


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Correction of a long-sighted eyeWear spectacles with convex lenses



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Wear spectacles with convex lenses

convex lens

light rays fromnear object

light rays appear to

come from afarther point

Class Practice 3:Class Practice 3: Chris is suffering from short-sightedness. What kind of spectacles should he wear?

He should wear a pair of spectacles with concave lenses.



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Chris is now looking at a distant object. Draw on thefollowing figure to show

(i)(i) how the light rays from the distant object travelinside the eyeball without spectacles, and

(ii)(ii) how the eye defect can be corrected with thespectacles.

Answer concave lens

Class Practice 4:Class Practice 4: A short-sighted person is looking at anear object in front of him. Draw in the following figure toshow the refraction of the two light rays by his eye lens.



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The image is formed _________________.Answer

on the retina

light rays fromnear object

Astigmatism Form distorted images



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Cause asymmetry of cornea shape Correction wear a non-spherical lens

Look at this set of lines to checkwhether you are suffering from

astigmatism



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CameraCamera

Structure of camera Factors affecting theamount of light entering a

camera Focusing

Camera functions like a human eye(1) lens(2) aperture

controls theexposure time of

Structure of camera4.3 Camera (SB p.125)


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(2) aperture(3) film(4) focusing

ring

(5) shutter

shutter

film

lens

focusing ring

aperture

image formedon the film

Note: The image formed onthe film is inverted and real.

focuses incominglight onto the film

adjusts the amountof light entering

the camera

plastic coveredwith light sensitive

chemical

adjusts the distancebetween lens and film

exposure time of the film to light

Control the amount of light entering a camera

(1) Size of aperture(2) Shutter speed

Factors affecting the amount of lightentering a camera

4.3 Camera (SB p.126)


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(1) Size of aperture

aperture

Controlled by a diaphragm (metal sheets) Control the intensity of light onto the film

diaphragm

Factors affecting the amount of lightentering a camera

4.3 Camera (SB p.127)

Control the amount of light entering a camera(2) Shutter speed

(1) Size of aperture(2) Shutter speed


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Open and closure of shutter depend on thechosen speed

Control the exposure time of the film to light

(2) Shutter speed

Focusing Properties

focusing ringfilm

Focusing4.3 Camera (SB p.127)


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p lens is mounted

on the focusing ring

Different object distance adjust the lens-to-film distance

(image distance) focus images on the film

Note: The process of adjusting

the lens-to-film distance is calledfocusing.

lens

g g

object

image

Focusing a far object Move lens close to the film



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(reduce image distance)

lens

object

image


Focusing a near object Moved lens away from the film


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object

image

(increase image distance)

Chapter 5Chapter 5


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Temperature, Heat andTemperature, Heat andInternal EnergyInternal Energy5.15.1 TemperatureTemperature

5.25.2 ThermometersThermometers

5.35.3 Heat and Internal EnergyHeat and Internal Energy

5.45.4 Specific Heat Capacity and EnergySpecific Heat Capacity and EnergyTransfer in Mixing ProcessTransfer in Mixing Process


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5.1 Temperature (SB p.140)

What is temperature?


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It tells how hot or cold an object is A hot body has a higher temperaturethan a cold one


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Celsius scale

5.1 Temperature (SB p.141)empera ure

scale


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In Hong Kong, the mostcommon temperature scale isCelsius scale

It was introduced by a Swedishastronomer, called AndersCelsius, in 1742

Celsiusscale

upper

Lower fixed point (or ice

empera ure

scale5.1 Temperature (SB p.142)


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upper fixed point

boilingwater

lower fixed point

melting ice

Upper fixed point (or steam

point) 100 C, temperatureof the steam over pure boilingwater at normal atmosphericpressure

point) 0 C, temperature for pure ice to melt at normalatmospheric pressure

Calibration divide theincluded region equally into 100divisions

Fahrenheit scale

5.1 Temperature (SB p.141)empera ure

scale


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1. Often used in hospitals and clinics to indicate thebody temperature

2. The melting point of ice is 32F

3. The steam point of boiling water is 212F

4. The normal body temperature is 98.6F


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Section 5.2Section 5.2ThermometersThermometers

Liquid-in glass

thermometers Other thermometers

How do you knowabout thermometers?

5.2 Thermometers (SB p.142)


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measure temperature

substance that hasthe property varieslinearly with the

temperature

Uses

Materials

Thermometer is a tool for measuringtemperature

5.2 Thermometers (SB p.142)


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Sensing propertySensing propertyProperty that varies linearlywith temperature: Length Colour

Electrical conductivity

Types of thermometers

5.2 Thermometers (SB p.146) Other thermometers


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Liquid-in-glass thermometer

Platinum resistance thermometer

Rotary thermometer Thermochromic thermometer

Liquid-in-glass thermometers

5.2 Thermometers (SB p.142) Liquid-in-glass thermometers


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Liquids in thecapillary glasstube expands or contracts linearlywith temperature

changes

Comparison of two liquid-in-glassthermometers

Mercury-in-glassthermometer

Alcohol-in-glassthermometer

5.2 Thermometers (SB p.143) Liquid-in-glass thermometers


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quick response to the changein temperature

slow response

can measure hightemperature (up to 357 C)

can measure lowtemperature (down to

110

C)mercury is poisonous, avoidinhaling its vapour once thethermometer is broken

alcohol is non-poisonous, butflammable, widely used inschool laboratories

no need to dye the liquid alcohol is colourless, it isdyed red for easier observation

more expensive cheaper

Clinical thermometers

Liquid-in-glass thermometers5.2 Thermometers (SB p.143)


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Constriction prevents the mercuryfrom falling back to thebulb, so as to maintainthe highesttemperature reading

Class Practice 1:Class Practice 1: A liquid-in-glass thermometer has column heights of 2.5 cm and 14 cm at ice point andsteam point respectively. After immersing thethermometer into an unknown liquid, the liquid column

Liquid-in-glass thermometers5.2 Thermometers (SB p.146)


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height becomes 9 cm. Find the temperature of the liquidand state the assumption you have made.Let the unknown temperature be T .

The equation is based on the assumption that the liquid expandswith the temperature increase.

Answer

=

=

T

T

)()(

)(

9 2.5

100 14 2.5

56.5C

linearly

Platinum resistance thermometer



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Property resistance increases when thetemperature rises

Method measure the resistance of a platinumwire that is in contact with the object

Temperature range 200C to 1 000C

Rotary thermometer Bimetallic strip

Other thermometers5.2 Thermometers (SB p.146)


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made up of twodifferent metal strips

when temperaturerises, one of the metalstrips expands more

metal strips bends

copper iron

copper

iron

rivet

At higher temperature:

Rotary thermometer Property



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consists of a coiled bimetallicstrip which bends whentemperature rises

Method

the strip coils up and movesthe pointer to indicate thetemperature

Application

measure the temperatures inovens and refrigerators

Thermochromic thermometer Property

Other thermometers5.2 Thermometers (SB p.147)


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colour changes withtemperature

Method

make use of colour to

indicate the temperatureTemperature range

20C to 40C

Application

measure the temperaturesof body and water inside afish tank


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Thermal equilibriumIf T A > T B

If T A = T Bno energy transfers and

5.3 Heat and internal energy (SB p.148) Heat


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energy transfers from A to B thermal equilibriumattains

After certaintime

energy transfers from A toB

no energy transfers

Law of conservation of energy

Heat5.3 Heat and internal energy (SB p.148)


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It states that in all energytransformation processes, energy cannotbe created or destroyed.

But energy can transfer from one body to another

change from one form to another

Heat

5.3 Heat and internal energy (SB p.149) Heat


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Heat is defined as theenergy transferred

between two bodies of different temperatures

Internal energy

5.3 Heat and internal energy (SB p.149) Internal energy


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Internal energy = Kinetic energy + Potential energy

originated frommotion of the

molecules

originated frombonding between

molecules

Intermolecular bonding

Internal energy5.3 Heat and internal energy (SB p.150)


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sphere

springpotential energy

kinetic energy

The bond between two

molecules is regardedas the spring linking twometal spheres

Temperature rises, kinetic energyincreases

5.3 Heat and internal energy (SB p.150) Internal energy


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When temperature rises molecules vibrate more

vigorously kinetic energy increases

State changes, potential energychanges

Internal energy5.3 Heat and internal energy (SB p.150)


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Weak bonds

are formed from theintermolecular attractions

between molecules are independent of indep endent of

temperaturetemp erature

Power 5.3 Heat and internal energy (SB p.151) Power


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Power =

P =

1 W = 1 J s 1

EnergyTime

E

t

e.g. A heater rated 50 W means 50 J of energy is transferred in 1 second



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Specific Heat Capacity andSpecific Heat Capacity andEnergy Transfer in MixingEnergy Transfer in Mixing

ProcessProcess Heat capacity Specific heat capacity

Energy transfer in mixingprocess


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Assume the temperature of body rises

Calculate heat capacity

Heat capacity

5.4 Specific heat capacity and energy transfer in mixing process (SB p.152)


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from T 1 to T 2 after it has absorbed anamount of energy E , the heat capacity of the body can be found by:

Heat capacity = Energy transfer

Temperature changes

i.e. C=E

T - T

Class Practice 2Class Practice 2

( )( ) T b h d d


Heat capacity


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(a)(a) Two substances are heated under the same physical condition and their temperature changes against time are

plotted in the graph:

Substance A has a temperature change than substance B.Therefore, substance A has a heat capacity thansubstance B.

Answer

smaller

higher

Temperature / C

Time / s

s u b s

t a n c e

B

s u b s t a n c e A


Contd)

Heat capacity



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(b)(b) In a heating process, thetemperature of an object rises from 22C to 95 C. If the heat capacity of the

object is 900 J C -1 , of heat is absorbed by the object. Oncethe he