GRADE – 10

CHAPTER – 10 (LIGHT-REFLECTION AND REFRACTION)

Mind Map:

CW:

1. Write the Index

2. Draw the mind map

3. Write the question and answers

HW:

1. Watch the video link sent to answer the questions orally in the class.

2. Read chapter- 10 (LIGHT-REFLECTION AND REFRACTION) and

answer the questions orally given in page.no.168 (textbook)

3. Write the back exercise questions (pg.No. 186) 7 & 9

4. Practice the worksheet

5. Complete Lab Manual Experiment N0: 10A, 10B, 11

STUDENT ACTIVITY :

1) To find focal length of concave and convex mirrors.

2) Draw Image formations by concave and covex mirrors on A4 sheet of

paper.

CLASS WORK NOTES QUESTION AND ANSWERS :

CHAPTER-10 (LIGHT- REFLECTION AND REFRACTION)

1. Define the following:

A.

a. Pole(P): It is the middle point of the spherical mirror

b. Centre of Curvature(C): It is the centre of which the mirror forms a part.

c. Radius of Curvature(R): It is the radius of sphere of which the mirror forms a part.

d. Principal axis: The line passing through the pole and the centre of curvature of the mirror.

e. Linear aperture: It is the diameter of circular boundary of the mirror.

f. Focal length (F): It is the distance between the focus and the pole of the mirror.

g. Focal plane: The vertical plane passing through the principal focus and perpendicular to the

principal axis.

2. Define the following:

(i) Principal Focus of a concave mirror

(ii) Principal Focus of a convex mirror

Draw the diagram for the above two cases

A. (i)A number of rays parallel to the principal axis when fall on a concave mirror after

reflection all meet at a point on the principal axis of the mirror. This point is called the principal

focus of the concave mirror. This property is called convergence. For diagram refer t.p.no:162,

fig 10.2(a)

(ii)A number of rays parallel to the principal axis when fall on a convex mirror after reflection

they all appear to come from a point on the principal axis of the mirror. This point is called

principal focus of the convex mirror. This property is called as divergence. For diagram refer

t.p.no:162, fig 10.2(b)

3. (i) Draw a ray diagram and mark the angle of incidence and angle of reflection in each

of the following cases.

(a) A ray passing parallel to the principal axis of a concave mirror

(b) A ray which is directed towards the principal focus of a convex mirror.

(c) A ray incident obliquely to the principal axis towards the pole of a concave mirror.

(ii) An object 2cm in size is placed 20cm in front of a concave mirror of focal length 15cm.

At what distance from the mirror should a screen be placed in order to obtain a sharp

image? Find the nature and size of the image formed.

A. (i) For diagrams refer (a) T.B p.no:164, fig 10.3(a),

(b) T.B P.no: 165, fig10.4 (b)

(c) fig 10.6 (a)

(ii) Object height, h = 2cm, Object distance, u = -20cm, Focal length, f = -15cm

Image distance, v=? Image height, h1 =? 𝟏

𝒇 =

𝟏

𝒖+

𝟏

𝒗

𝟏

𝒗 =

𝟏

𝒇−

𝟏

𝒖

𝟏

𝒗 =

𝟏

−𝟏𝟓−

𝟏

−𝟐𝟎 =

−𝟏

𝟏𝟓+

𝟏

𝟐𝟎 =

−𝟒+𝟑

𝟔𝟎 =

−𝟏

𝟔𝟎

v = -60cm

m = 𝒉𝟏

𝒉 =

−𝒗

𝒖h1 =

−𝒗

𝒖×h

h1= −(−𝟔𝟎)

−𝟐𝟎 x 2= -6cm

Object is placed between F and C, Image is formed beyond C

Nature: Image formed is real and inverted

Size: Magnified

4. (a) Draw ray diagram in the following cases to show the position and nature of the

image formed by a concave mirror when an object is placed:

(i)Between Pole and Focus

(ii)Focus and Centre of Curvature

(iii) At the Centre of curvature

(iv) Beyond C

(b) How will the nature and position of image formed changes in case all the cases if the

concave mirror is replaced by convex mirror? Draw diagram to justify answer.

A. (a) (i) For diagram refer TB p. no: 166, 10.7(f)

Virtual, erect and magnified Image is formed behind the mirror.

(ii) For diagram refer TB p. no:166, 10.7(d)

Real, inverted and enlarged Image is formed beyond C.

(iii) For diagram refer TB p. no:166, 10.7(c)

Real, inverted and same size Image is formed at C.

(iii) For diagram refer TB p. no:166, 10.7(b)

Real, inverted and diminished Image is formed between F and C.

(b) In all the cases virtual, erect and diminished image will be formed between P and F behind

the mirror.

5. Name the type of mirror used in the following situations:

(a)Headlights of a car

(b)Side/rear view mirror of a vehicle and

(c) Solar furnace

Support your answer with reasons.

A. (a) Headlights of a car use a concave mirror.

A concave mirror renders the rays parallel when object is placed at its principal focus. The bulb

of headlight is placed at the focus of concave mirror. The rays reflected from the mirror are in

the form of a strong parallel beam. The beam goes straight and makes the distant objects visible

for safe driving.

(b) Side/rear view mirror of a vehicle is convex mirror because of its largest field of view.

Convex mirror always forms an erect and diminished image.

(c) A solar furnace uses a concave mirror. The object is placed at the focus of concave mirror to

get heated. The parallel rays coming from the sun become incident on the mirror and get

reflected at focus. Thus sufficient energy is received from the sun and collected at one point

(focus) to heat the object.

6. (a) Define principal focus, focal length and principal axis of a lens.

(b)Draw ray diagram to show the principal focus of a Convex and Concave lens.

A. (a) Principal focus: Parallel rays after refraction from the lens, either converge at or diverge

from a point on the principal axis. This point on the principal axis is called the principal focus

of the lens.

Focal length: The distance between optical centre and focus is called focal length.

Principal axis: An imaginary straight line passing through the two centres of curvature of a

lens is called Principal axis.

(b) For diagrams refer TB p. no: 176, fig 10.12

7. (a) State laws of refraction.

(b) What is meant by the terms absolute refractive and relative refractive index? The

speed of light in transparent medium is 0.5 times that of the speed in vacuum. Find

refractive index of the medium.

(c) How should a ray of light be incident on a rectangular glass slab so that it comes out

from the opposite side of the slab without being displaced? Draw a ray diagram to

illustrate.

A. (a) The laws of refraction are

(i) The incident ray, the refracted ray and normal at the point of interface of two media at

the point of incidence, all lie in the same plane.

(ii) The ratio of the sine of the angle of incidence to the sine of angle of refraction is a

constant, for the light of a given colour and for the given pair of media.

n = 𝒔𝒊𝒏𝒊

𝒔𝒊𝒏𝒓 = constant

(b)(i) The absolute refractive index of a medium is defined as the ratio of speed of light in

vacuum to the speed of light in the medium.

Refractive index, n= 𝒔𝒑𝒆𝒆𝒅𝒐𝒇𝒍𝒊𝒈𝒉𝒕𝒊𝒏𝒗𝒂𝒄𝒖𝒖𝒎

𝒔𝒑𝒆𝒆𝒅𝒐𝒇𝒍𝒊𝒈𝒉𝒕𝒊𝒏𝒎𝒆𝒅𝒊𝒖𝒎 =

𝒄

𝒗

The relative refractive index is defined as the ratio of refractive index of medium 1 to medium2

(or) speed of light in medium1 to medium2.

Relative refractive index, n12= 𝒏𝟏

𝒏𝟐 =

𝒗𝟐

𝒗𝟏

Refractive index, n = 𝒄

𝒗 =

𝒄

𝟎.𝟓𝒄 = 2

(c) The ray of light should be incident normally to the surface of the glass slab.

900

8. (a)Define power of a lens and state its SI unit.

(b) Two thin lenses of focal length+10cm and -5cm are kept in contact. Find the focal

length and power of this combination of lenses.

A. (a) Degree of convergence or divergence of a lens is its power.

Its SI unit is Dioptre (D) and has a focal length of 1m.

Concave lens has negative power and convex lens has positive power.

(b) 𝟏

𝒇 =

𝟏

𝒇𝟏 +

𝟏

𝒇𝟐 =

𝟏

𝟏𝟎 +

𝟏

−𝟓 =

𝟏

𝟏𝟎 -

𝟏

𝟓 =

𝟏−𝟐

𝟏𝟎 =

−𝟏

𝟏𝟎

P = 𝟏

𝒇 =

𝟏𝟎𝟎

−𝟏𝟎 =-10D

9. A convex lens of focal length 20cm is placed at a distance of 24cm from the screen.

How far from the lens should an object be placed so as to form a real image on the screen?

Also find the nature and magnification of the image produced by the lens.

A. Given focal length, f = 20cm, image distance, v=24cm, object distance, u=?

Magnification, m=?

From Lens formula, 𝟏

𝒇 =

𝟏

𝒗−

𝟏

𝒖

-𝟏

𝒖 =

𝟏

𝒇–

𝟏

𝒗 =

𝟏

𝟐𝟎–

𝟏

𝟐𝟒=

𝟔−𝟓

𝟏𝟐𝟎=

𝟏

𝟏𝟐𝟎 u = -120cm

m = 𝒗

𝒖 =

𝟐𝟒

−𝟏𝟐𝟎 = -0.2

Negative sign indicates that the image is real and inverted.

10. Draw labeled ray diagram in each of the following cases to show the position and

nature of the image formation when the object is placed:

(a) Between optical centre O and focus F1 of a convex lens.

(b) At infinity of a concave lens.

(c) Between a concave lens and infinity

(d) Between a principal focus F1 and centre of curvature C1of a convex lens.

(e) At 2F1 of convex lens

A. Refer TB p.no: 180

(a) fig 10.16(f)

(b) fig 10.17(a)

(c) fig 10.17(b)

(d) fig 10.16(d)

(e) fig 10.16(c)

11. A student has focused the image of a candle flame on a white screen using a concave

mirror. The situation is as given below:

Length of the flame: 1.5cm

Focal length of the mirror: 12cm

Distance of flame from the mirror: 18cm

If the flame is perpendicular to the principal axis of the mirror, then calculate the

following:

(a) Distance of the image from the mirror

(b) Length of the image

If the distance between the mirror and the flame is reduced to 10cm, then what would be

observed on the screen? Draw ray diagram to justify your answer for this situation.

A. Given:

height of object, h= +1.5cm; focal length, f = -12cm; object distance , u= - 18cm; image

distance, v=?; height of image, h1=?

(a) Applying mirror formula,

1 1 1

1 1 1

1 1 1 1 3 2 1

( 12) ( 18) 12 18 36 36

f v u

v f u

= +

= −

− − + −= − = + = =

− −

v= - 36cm

(b) 1 361.5

18

v cmh xh x cm

u cm

−= − = −

=-3cm (Magnified, inverted image)

If u= - 10cm, no distinct image would be formed on the screen. In this case the image formed

will be virtual.

12. A truck uses a convex mirror as view finder whose radius of curvature is 2.0m. A

maruti car is coming behind the truck at a distance of 10m. What will be the position of

the image of the car and size of the image of the car when observed by the driver of the

truck through the convex mirror?

A. For convex mirror, we have given, u= - 10m, R= 2.0 m

So, 2.0

1.02 2

R mf m= = =

Using the mirror formula, 1 1 1

u v f+ =

We get 1 1 1 1 1 11 10

, 0.91.0 10 10 11

or v mv f u= − = + = = =

Thus, the car would appear at 0.9m from the convex mirror. We know that 10

111

10 11

vm

u

−

= − − = =−

Thus, size of the image of the car will be a fraction of 1

11 the actual size of the car through the

convex mirror.

13. A student focused the image of a candle flame on a white screen using a convex lens.

He noted down the position of the candle, screen and the lens as under

Position of candle = 12.0cm

Position of convex lens = 50.0 cm

Position of the screen =88.0cm

(i) What is the focal length of the convex lens?

(ii) Where will the image be formed if he shifts the candle towards the lens at a position of

31.0cm?

(iii) What will be the nature of the image formed if he further shifts the candle towards the

lens?

(iv) Draw a ray diagram to show the formation of the image in case (iii) as said above.

A. (i) Here, u= distance of candle from the lens

= (50 – 12) cm = 38 cm

According to sign convention, u = - 38cm

Now, v = Distance of screen from the lens

= (88 – 50) cm = 38 cm

As per sign convention, v = +38cm

Using the formula,

1 1 1

1 1 1

38 38

v u f

f

− =

+ =

𝟏

𝒇 =

𝟐

𝟑𝟖f=

38

2= 19cm

(ii)If the student shifts the candle towards the lens at a position of 31.0cm, object distance

u=(50-31) = 19cm. Thus, candle lies at the focus. Hence, image will be formed at infinity.

(iii) If the candle is further shifted towards the lens, the candle lies between the optical centre

and focus of the lens. Thus a virtual, erect and magnified image is formed on the same side as

the object.

(iv)

14. A real image, 4

5 size of the object is formed 18 cm from a lens. Calculate the focal

length of the lens.

A. Since the image is real and diminished, the lens must be convex and the object must be

placed beyond 2F.

Given: v = +18cm 1 4

5

h

h

−= [

1hm

h= is negative for real image]

f=?

We have, 1h v

mh u

= =

4

5

v

u

−=

4u= -5v

And 4u=-5 x 18 cm

u = - 22.5cm

Also focal length is given by

1 1 1

f v u= −

𝟏

𝒇

1 1 1 1 9

18 22.5 18 22.5 90= − = + =

−

f=10 cm

SUNFLOWER VEDIC SCHOOL

CHAPTER- : LIGHT-REFLECTION AND REFRACTION

1. An object is placed at a distance of 0.25 m in front of a plane mirror. The distance

between the object and image will be

(a) 0.25 m

(b) 1.0 m

(c) 0.5 m

(d) 0.125 m

2. The angle of incidence for a ray of light having zero reflection angle is

(a) 0

(b) 30°

(c) 45°

(d) 90°

3. For a real object, which of the following can produce a real image?

(a) Plane mirror

(b) Concave mirror

(c) Concave lens

(d) Convex mirror

4. Which of the following mirror is used by a dentist to examine a small cavity?

(a) Convex mirror

(b) Plane mirror

(c) Concave mirror

(d) Combination of convex and concave mirror

[2021-22] Work Sheet

Name: __________ Date: __________

Roll No: _______ Mentor:

Grade : 10 Principal Sign: ______

Sub: Physics Checked by :________

5. An object at a distance of 30 cm from a concave mirror gets its image at the same point.

The focal length of the mirror is

(a) – 30 cm

(b) 30 cm

(c) – 15 cm

(d) +15 cm

6. An object at a distance of + 15 cm is slowly moved towards the pole of a convex mirror.

The image will get

(a) shortened and real

(b) enlarged and real

(c) enlarge and virtual

(d) diminished and virtual

7. A concave mirror of radius 30 cm is placed in water. It’s focal length in air and water

differ by

(a) 15

(b) 20

(c) 30

(d) 0

8. A concave mirror of focal length 20 cm forms an image having twice the size of object.

For the virtual position of object, the position of object will be at

(a) 25 cm

(b) 40 cm

(c) 10 cm

(d) At infinity

9. The image formed by concave mirror is real, inverted and of the same size as that of the

object. The position of object should be

(a) at the focus

(b) at the centre of curvature

(c) between focus and centre of curvature

(d) beyond centre of curvature

10. The nature of the image formed by concave mirror when the object is placed between the

focus (F) and centre of curvature (C) of the mirror observed by us is

(a) real, inverted and diminished

(b) virtual, erect and smaller in size

(c) real, inverted and enlarged

(d) virtual, upright and enlarged

11. The nature of image formed by a convex mirror when the object distance from the mirror

is less than the distance between pole and focal point (F) of the mirror would be

(a) real, inverted and diminished in size

(b) real, inverted and enlarged in size

(c) virtual, upright and diminished in size

(d) virtual, upright and enlarged in size

12. If a man’s face is 25 cm in front of concave shaving mirror producing erect image 1.5

times the size of face, focal length of the mirror would be

(a) 75 cm

(b) 25 cm

(c) 15 cm

(d) 60 cm

13. As light travels from a rarer to a denser medium it will have

(a) increased velocity

(b) decreased velocity

(c) decreased wavelength

(d) both (b) and (c)

14. The distance between the optical centre and point of convergence is called focal length in

which of the following cases?

15. If the power of a lens is – 2 D, what is its focal length?

(a) +50 cm

(b) -100 cm

(c) -50 cm

(d) +100 cm

16. A student does the experiment on tracing the path of a ray of light passing through a

rectangular glass slab for different angles of incidence. He can get a correct measure of

the angle of incidence and the angle of emergence by following the labeling indicated in

figure:

(a) I

(b) II

(c) III

(d) IV

II Assertion and reason type questions

Two statements are given – one labeled Assertion(A) and the other labeled Reason

(R). Select the correct answer to these questions from the codes (i),(ii),(iii)and(iv)as

given below

i) Both A and B are true and R is correct explanation of assertion.

ii) Both A and B are true but R is not the correct explanation of assertion.

iii) A is true but R is false.

iv) A is false but R is true.

1. Assertion: Incident light is reflected in only one direction from a smooth surface.

Reason: Since the angle of incidence and the angle of reflection are same, a beam of

parallel rays of light falling on a smooth surface is reflected as a beam of parallel light

rays in one direction only.

2. Assertion: The word AMBULANCE on the hospital vans is written in the form of its

mirror as

Reason: The image formed in a plane mirror is same size of the object.

3. Assertion: The object distance is the distance of the object from the lens.

Reason: It is measured from the object to the optical centre of the Lens.

4. Assertion: In the dispersion of white light by a prism, the red light bends the least.

Reason: The frequency of red light is the highest.

5. Assertion: Convex mirror is preferred for rearview mirror in vehicles.

Reason: The field view of a convex mirror is lesser than that of concave mirror.

6. Assertion: Dentists use concave mirror.

Reason: Concave mirrors are converging mirrors.

7. Assertion: Power of a concave lens is negative.

Reason: Focal length of concave lens is taken on left hand side.

8. Assertion: Light travelling from air into a glass slab bends away from the normal.

Reason: Light moves faster in air than glass slab.

9. Assertion: An object placed in front of a convex lens form the image of same size.

Reason: Object is place between center of curvature and focus.

III Fill in the Blanks

1. Light shows the phenomenon of reflection, refraction and ______________

2. The speed of light in vacuum is ____________

3. Power of a lens is the______________ of its focal length.

4. The SI unit of power is _____________

5. A ___________ lens will always give a virtual, erect and diminished image, irrespective

of the position of the object.

6. A positive sign in the value of magnification indicates that the image is ____________

7. A __________ mirror is used as a head mirror by the doctors to concentrate light on the

body parts to be examined.

8. No matter how far you stand from a spherical mirror, your image appears erect. The

mirror may be __________________

9. _____________mirror is used as a security mirror in shops and on roads at sharp bends

and concealed entrances.

10. The refractive index of a transparent medium is the ratio of the speed of light in

____________ to that in the ________________

11. The focal length of a concave lens is considered to be _____________

12. The focal length of a lens is the distance between _____________and _____________of

the lens.