54
LIGHT : LIGHT : REFLECTION REFLECTION AND AND REFRACTION REFRACTION

LIGHT : REFLECTION AND REFRACTION

  • Upload
    chaman

  • View
    166

  • Download
    20

Embed Size (px)

DESCRIPTION

LIGHT : REFLECTION AND REFRACTION. LIGHT. Light is a form of electromagnetic radiation that causes the sensation of sight. It is an indispensable tool without which we cannot explore the colorful beauty of nature. - PowerPoint PPT Presentation

Citation preview

Page 1: LIGHT : REFLECTION AND REFRACTION

LIGHT : LIGHT : REFLECTIOREFLECTIO

N AND N AND REFRACTIOREFRACTIO

NN

Page 2: LIGHT : REFLECTION AND REFRACTION

LIGHTLIGHT Light is a form of electromagnetic radiation Light is a form of electromagnetic radiation

that causes the sensation of sight. that causes the sensation of sight. It is an indispensable tool without which we It is an indispensable tool without which we

cannot explore the colorful beauty of nature.cannot explore the colorful beauty of nature. The blue sky, the rainbow, the red of the The blue sky, the rainbow, the red of the

sunrise and sunset, the twinkling of stars, the sunrise and sunset, the twinkling of stars, the radiance of sparkling diamonds and pearls, radiance of sparkling diamonds and pearls, and shining color of gems are just some of the and shining color of gems are just some of the natural wonders of light and color.natural wonders of light and color.

Page 3: LIGHT : REFLECTION AND REFRACTION

NATURE OF LIGHTNATURE OF LIGHT Light is an electromagnetic wave.Light is an electromagnetic wave. These waves do not require any These waves do not require any

medium for their propagation.medium for their propagation. The wavelength of visible light waves is The wavelength of visible light waves is

very small, only about 4 x 10very small, only about 4 x 10-7-7m to 8 x 10m to 8 x 10--

77mm The speed of light wave depends on The speed of light wave depends on

the nature of the medium through the nature of the medium through which they pass.which they pass.

The speed of light waves in vacuum is The speed of light waves in vacuum is very high, being 3 x 10very high, being 3 x 1088 m/s. m/s.

Page 4: LIGHT : REFLECTION AND REFRACTION

Light provides us means of Light provides us means of communication. communication.

The fibre-optic cables The fibre-optic cables consisting of many glass consisting of many glass fibres transmit hundreds of fibres transmit hundreds of telephone conversations telephone conversations over long distances.over long distances.

Page 5: LIGHT : REFLECTION AND REFRACTION

REFLECTION OF REFLECTION OF LIGHTLIGHT

When light falls on the surface of an When light falls on the surface of an object, it may beobject, it may be

i) absorbedi) absorbed ii) transmitted iii) reflectedii) transmitted iii) reflected When light falls on the surface of an When light falls on the surface of an

object, some of it is sent back. The object, some of it is sent back. The process of sending back the light rays process of sending back the light rays which fall on the surface of an object, which fall on the surface of an object, is called reflection of light.is called reflection of light.

Page 6: LIGHT : REFLECTION AND REFRACTION

IMAGESIMAGES

An image is formed when the light rays An image is formed when the light rays coming from an object meet ( or appear to coming from an object meet ( or appear to meet) at a point, after reflection from a meet) at a point, after reflection from a mirror ( or refraction from a lens).mirror ( or refraction from a lens).

Real Image – If the light rays actually meet Real Image – If the light rays actually meet after reflection or refraction is called real after reflection or refraction is called real image. It can be obtained on a screen.image. It can be obtained on a screen.

Virtual Image – If the light rays appear to Virtual Image – If the light rays appear to meet after reflection or refraction, then it is meet after reflection or refraction, then it is called virtural image. It can’t be obtained on called virtural image. It can’t be obtained on a screen.a screen.

Page 7: LIGHT : REFLECTION AND REFRACTION

LAWS OF REFLECTION OF LAWS OF REFLECTION OF LIGHTLIGHT

FIRST LAWFIRST LAW – – The angle of The angle of incidence (i) is equal to the incidence (i) is equal to the angle of reflection (r ) angle of reflection (r )

SECOND LAWSECOND LAW – The incident ray, – The incident ray, the normal to the mirror at the the normal to the mirror at the point of incidence, and the point of incidence, and the reflected ray, all lie in the same reflected ray, all lie in the same plane.plane.

Page 8: LIGHT : REFLECTION AND REFRACTION

FORMATION OF IMAGE IN FORMATION OF IMAGE IN A PLANE MIRRORA PLANE MIRROR

The characteristics of image formed The characteristics of image formed in a plane mirror are in a plane mirror are

i) image is virtual i) image is virtual ii) image is erect ii) image is erect iii) image is of the same size of the iii) image is of the same size of the

object. iv) image is formed as far object. iv) image is formed as far behind the mirror, as the object is in behind the mirror, as the object is in front of it. front of it.

v) image is laterally inverted.v) image is laterally inverted.

Page 9: LIGHT : REFLECTION AND REFRACTION

SPHERICAL MIRRORSPHERICAL MIRROR

A spherical mirror is that mirror whose A spherical mirror is that mirror whose reflecting surface is the part of a hollow reflecting surface is the part of a hollow sphere of glass.sphere of glass.

It is of two types :It is of two types : i) concave mirrors i) concave mirrors ii) convex mirrorsii) convex mirrors

Page 10: LIGHT : REFLECTION AND REFRACTION

RULES FOR FORMATION OF RULES FOR FORMATION OF IMAGE BY SPHERICAL IMAGE BY SPHERICAL

MIRRORSMIRRORS When an object is placed before a spherical When an object is placed before a spherical

mirror, an image is formed. The image is mirror, an image is formed. The image is formed at that point where at least two formed at that point where at least two reflected rays intersect (or appear to reflected rays intersect (or appear to intersect).intersect).

Now to find out the position of an image Now to find out the position of an image formed by a concave mirror, only two rays formed by a concave mirror, only two rays light is required. We use those rays whose light is required. We use those rays whose path is certain, the diagram formed in this path is certain, the diagram formed in this way is called as ray diagram. way is called as ray diagram. Continued…Continued…

Page 11: LIGHT : REFLECTION AND REFRACTION

To draw ray diagram, the following rules To draw ray diagram, the following rules are used: are used:

i) A ray of light parallel to the principal i) A ray of light parallel to the principal axis of the mirror, passes through the axis of the mirror, passes through the focus after reflection from the mirror.focus after reflection from the mirror.

ii) A ray of light passing from the center ii) A ray of light passing from the center of curvature of the mirror is reflected of curvature of the mirror is reflected back along the same path.back along the same path.

iii) A ray of light passing through the iii) A ray of light passing through the focus of a concave mirror becomes focus of a concave mirror becomes parallel to the principal axis.parallel to the principal axis.

An image of any point is formed at that An image of any point is formed at that point where at least two reflected rays point where at least two reflected rays intersect or appear tointersect or appear to intersect. intersect.

Page 12: LIGHT : REFLECTION AND REFRACTION

IMAGE FORMATION BY IMAGE FORMATION BY CONCAVE MIRRORCONCAVE MIRROR

position of position of the objectthe object

Position of Position of the imagethe image

Size of the Size of the imageimage

Nature of the Nature of the imageimage

At infinity At infinity At the focus At the focus FF

Highly Highly DiminishedDiminished

Real and Real and InvertedInverted

Beyond CBeyond C Between F Between F and Cand C

DiminishedDiminished Real and Real and InvertedInverted

At CAt C At CAt C Same sizeSame size Real and Real and InvertedInverted

Between C Between C and Fand F

Beyond CBeyond C EnlargedEnlarged Real and Real and InvertedInverted

At FAt F At infinityAt infinity Highly Highly enlargedenlarged

Real and Real and InvertedInverted

Between P Between P and Fand F

Behind the Behind the mirrormirror

Enlarged Enlarged Virtual and Virtual and irectirect

Page 13: LIGHT : REFLECTION AND REFRACTION

IMAGE FORMATION BY IMAGE FORMATION BY CONVEX MIRRORCONVEX MIRROR

Position of Position of the objectthe object

Position of Position of the imagethe image

Size of Size of the imagethe image

Nature Nature of the of the imageimage

At infinityAt infinity At the focus At the focus F, behind F, behind the mirrorthe mirror

Highly Highly diminishediminished, point d, point sizesize

Virtual Virtual and and erecterect

Between Between infinity and infinity and the pole of the pole of the mirrorthe mirror

Between p Between p and F, and F, behind the behind the mirrormirror

diminishediminishedd

Virtual Virtual and and erecterect

Page 14: LIGHT : REFLECTION AND REFRACTION

NEW CARTESIAN SIGN NEW CARTESIAN SIGN CONVENTIONCONVENTION

Height downwards (-ve)

Direction of

Incident light

Incident light (-ve)

Direction against Distance along

Incident light (+ve)

Height upwards (+ve)

Height downwards (-ve)

Height downwards (-ve)

Objects on the left

N

M

PX’ X

Y’

Y

B’

A’

A

B

Page 15: LIGHT : REFLECTION AND REFRACTION

MIRROR FORMULAMIRROR FORMULA

A

BC P

M

N

A’

B’

h

h’ F

R

f

v

Fig 2.3

u

Page 16: LIGHT : REFLECTION AND REFRACTION

FORMATION OF IMAGE BY FORMATION OF IMAGE BY CONVEX MIRRORCONVEX MIRROR

A

B

M

N

C

E

D

A’

B’ FP

Page 17: LIGHT : REFLECTION AND REFRACTION

We will now obtain a relation between We will now obtain a relation between the object-distance (the object-distance (uu), the image –), the image –distance (distance (vv) and the focal length () and the focal length (ff) of ) of the spherical mirror having small the spherical mirror having small aperture (much less than the radius of aperture (much less than the radius of curvature (curvature (RR). This relation is called ). This relation is called Mirror Formula.Mirror Formula. It remains the same in It remains the same in all types of physical situations, whether the all types of physical situations, whether the image is real or virtualimage is real or virtual

Page 18: LIGHT : REFLECTION AND REFRACTION

We now derive the mirror formula for a We now derive the mirror formula for a concave mirror producing a real image in concave mirror producing a real image in fig 2.3.fig 2.3.

When the object When the object ABAB is of size or is of size or height (height (hh) is placed on the left in ) is placed on the left in front of the concave mirror front of the concave mirror MNMN, , beyond its centre of curvature beyond its centre of curvature CC, The , The image formed is real, inverted and image formed is real, inverted and diminished in size (diminished in size (h’h’))

Page 19: LIGHT : REFLECTION AND REFRACTION

Using the New Cartesian Sign Convention, Using the New Cartesian Sign Convention, we have we have

Object distance = PB = - u Object distance = PB = - u Image distance = PB’= -vImage distance = PB’= -v Focal length Focal length = PF = -f = PF = -f Radius of curvature = PC = -RRadius of curvature = PC = -R Now in fig 2.3 , the right angle triangles ∆ Now in fig 2.3 , the right angle triangles ∆

A’B’P and ∆ ABP, are similar, so thatA’B’P and ∆ ABP, are similar, so that A’B’ A’B’ PB’ PB’ -v -v vv

AB PB -u uAB PB -u u3,1

Page 20: LIGHT : REFLECTION AND REFRACTION

Similarly in the right angled triangles, Similarly in the right angled triangles, ABC and A’B’C’ are similar, so thatABC and A’B’C’ are similar, so that

A’B’ CB’A’B’ CB’ AB CBAB CB As we measure all distances from the As we measure all distances from the

pole P, we havepole P, we have CB’ = PC – PB’CB’ = PC – PB’ CB = PB – PCCB = PB – PC Using equation 3.2 we getUsing equation 3.2 we get A’B’ PC – PB’ (-R)-(- v) -R + vA’B’ PC – PB’ (-R)-(- v) -R + v AB PB – PC (-u)–(-R) -u + RAB PB – PC (-u)–(-R) -u + R

3.3

Page 21: LIGHT : REFLECTION AND REFRACTION

Comparing Eqs. (3.1) and (3.3), we getComparing Eqs. (3.1) and (3.3), we get - R + v v- R + v v - u + R u- u + R u Or, uR + vR = 2uvOr, uR + vR = 2uv Dividing both sides by uvR, we getDividing both sides by uvR, we get 1/v + 1/u = 2/R1/v + 1/u = 2/R -------------- (3.4) -------------- (3.4) When the object AB is taken at a very large When the object AB is taken at a very large

distance ( at infinity), as shown the image distance ( at infinity), as shown the image is formed at the focus F. Thus, when u =∞ , is formed at the focus F. Thus, when u =∞ , v = f, putting the values in eq 3.4 , we getv = f, putting the values in eq 3.4 , we get

1/f + 1/∞ = 2 / R or f = R/2 ------ (3.5)1/f + 1/∞ = 2 / R or f = R/2 ------ (3.5)

Page 22: LIGHT : REFLECTION AND REFRACTION

MAGNIFICATIONMAGNIFICATION The ratio between the height of the image The ratio between the height of the image

produced by the spherical mirror to the produced by the spherical mirror to the height of the object is called linear height of the object is called linear magnification.magnification.

Height of the imageHeight of the image

Linear magnification = --------------------------Linear magnification = --------------------------

Height of the objectHeight of the object

hihi

M = ---------M = --------- = v/u= v/u

hoho

Page 23: LIGHT : REFLECTION AND REFRACTION

REFRACTION OF LIGHT AND ITS REFRACTION OF LIGHT AND ITS LAWSLAWS

the ratio of sine of angle of incidence to the sine the ratio of sine of angle of incidence to the sine of angle of refraction is constant. Thus, angle of of angle of refraction is constant. Thus, angle of incidence I and the angle or refraction r are incidence I and the angle or refraction r are related as related as

Sin iSin i

------- = n------- = n2121

sin r sin r n n2121 is a constant and is is a constant and is called the refractive index of second medium with called the refractive index of second medium with respect to first medium. It is also known as respect to first medium. It is also known as Snell’s Snell’s law of refraction.law of refraction.

ii) The incident ray, the refracted and the normal ii) The incident ray, the refracted and the normal at the point of incidence lie in the same plane.at the point of incidence lie in the same plane.

Page 24: LIGHT : REFLECTION AND REFRACTION

REFRACTIVE INDEXREFRACTIVE INDEX Ans:- For two media and for a light of a particular color, Ans:- For two media and for a light of a particular color,

the ratio of sine of incidence angle and sine of the ratio of sine of incidence angle and sine of refraction angle is called refractive index of second refraction angle is called refractive index of second medium with respect to first.medium with respect to first.

Sin iSin i

--------------------- = n--------------------- = n2121

sin rsin r if motion of light is in reverse direction means from if motion of light is in reverse direction means from

medium 2 to medium 1, refractive index is reversiblemedium 2 to medium 1, refractive index is reversible

nn1212 = sin r/ sin i = 1/n = sin r/ sin i = 1/n2121

if velocity of light is v1 in first medium and v2 in second if velocity of light is v1 in first medium and v2 in second medium, medium,

nn21 21 = velocity of light in first medium(v= velocity of light in first medium(v11)/ )/ velocity of light in second medium (vvelocity of light in second medium (v22))

Page 25: LIGHT : REFLECTION AND REFRACTION

Refractive index of water is 4/3 and Refractive index of water is 4/3 and glass is 3/2 with respect to air. What is glass is 3/2 with respect to air. What is

refractive of glass with respect to refractive of glass with respect to water.water.

Ans;- refractive index of air , nAns;- refractive index of air , n11 = 1.00 = 1.00

Thus, refractive index of water w.r.t. air, nThus, refractive index of water w.r.t. air, n2121 = n= n22 = 4/3 = 4/3

Refractive index of glass w.r.t. air = nRefractive index of glass w.r.t. air = n3131 = = nn33 = 3/2= 3/2

Refractive index of glass w.r.t water = nRefractive index of glass w.r.t water = n3232

nn3232 = n = n3131 x n x n1212 = n = n3131/ n/ n2121 = n = n33/n/n22 = = (3/2)/(4/3) = 9/8 = 1.125(3/2)/(4/3) = 9/8 = 1.125

Page 26: LIGHT : REFLECTION AND REFRACTION

RULES FOR IMAGE FORMATION RULES FOR IMAGE FORMATION IN SPHERICAL LENSESIN SPHERICAL LENSES

1)1) A ray from the object parallel to the A ray from the object parallel to the principal axis after refraction passes principal axis after refraction passes through the second principal focus F2 through the second principal focus F2 ( in a convex lens) or appears to diverge ( in a convex lens) or appears to diverge ( in a concave lens) from the first ( in a concave lens) from the first principal focus F1principal focus F1

2)2) A ray of light passing through the first A ray of light passing through the first principal focus ( in a convex lens), or principal focus ( in a convex lens), or appearing to meet at it ( in a concave appearing to meet at it ( in a concave lens) emerges parallel to the principal lens) emerges parallel to the principal axis after refraction.axis after refraction.

Page 27: LIGHT : REFLECTION AND REFRACTION

3) A ray of light passing through the 3) A ray of light passing through the optical centre of the lens, emerges optical centre of the lens, emerges without any deviation after without any deviation after refraction.refraction.

Page 28: LIGHT : REFLECTION AND REFRACTION

IMAGE FORMATION BY IMAGE FORMATION BY CONVEX LENSCONVEX LENS

position of position of the objectthe object

Position of Position of the imagethe image

Size of the Size of the imageimage

Nature of the Nature of the imageimage

At infinity At infinity At the focus At the focus F2F2

Highly Highly DiminishedDiminished

Real and Real and InvertedInverted

Beyond Beyond 2F12F1

Between F2 Between F2 and 2F2and 2F2

DiminishedDiminished Real and Real and InvertedInverted

At 2F1At 2F1 At F2At F2 Same sizeSame size Real and Real and InvertedInverted

Between Between F1 and F1 and 2F12F1

Beyond 2F2Beyond 2F2 EnlargedEnlarged Real and Real and InvertedInverted

At F1At F1 At infinityAt infinity Highly Highly enlargedenlarged

Real and Real and InvertedInverted

Between Between F1 and OF1 and O

On the On the same side same side of lensof lens

Enlarged Enlarged Virtual and Virtual and irectirect

Page 29: LIGHT : REFLECTION AND REFRACTION

IMAGE FORMATION IN CONVEX IMAGE FORMATION IN CONVEX LENSLENS

CONVEX LENSCONVEX LENS

A

N

M

F12F1B

C

A

B’

A’F2O

Page 30: LIGHT : REFLECTION AND REFRACTION

LENS FORMULALENS FORMULA

N

M

F12F1

C

2F2

B’

A’F2O

A

B

Page 31: LIGHT : REFLECTION AND REFRACTION

Here object distance = OB = -uHere object distance = OB = -u Image distance Image distance = OB’ = v = OB’ = v Focal lengthFocal length = OF2= f = OF2= f AB = OCAB = OC ∆ ∆ ABO ~ ∆ A’B’O are similarABO ~ ∆ A’B’O are similar A’B’/AB = OB’/OB = v/-u ……….eq. –(i)A’B’/AB = OB’/OB = v/-u ……….eq. –(i) Similarly ∆ OCE2 ~ ∆A’B’F2Similarly ∆ OCE2 ~ ∆A’B’F2 A’B’/OC = F2B’/OF2, As AB = OC, thenA’B’/OC = F2B’/OF2, As AB = OC, then A’B’/AB = F2B’/OF2 = ( OB’- OF2)/OF2 = A’B’/AB = F2B’/OF2 = ( OB’- OF2)/OF2 =

(v-f)/f(v-f)/f …… ……..eq. – ..eq. –

(ii)(ii)

Page 32: LIGHT : REFLECTION AND REFRACTION

From eq. (i) & (ii) we get, -v/u = v-f/fFrom eq. (i) & (ii) we get, -v/u = v-f/f On cross multiplication and dividing both On cross multiplication and dividing both

sides by uvf, we get,sides by uvf, we get,

1/v – 1/u = 1/f1/v – 1/u = 1/f

Page 33: LIGHT : REFLECTION AND REFRACTION

IMAGE FORMATION IN IMAGE FORMATION IN CONCAVE LENSCONCAVE LENS

Object is at infinity and the image is at F1

OF12F1

Page 34: LIGHT : REFLECTION AND REFRACTION

When the object is between O When the object is between O and Infinityand Infinity

B

A

2F1F1

A'

B’ O

Page 35: LIGHT : REFLECTION AND REFRACTION

Image formation in concave Image formation in concave lenslens

Position of Position of the objectthe object

Position of Position of the imagethe image

Size of the Size of the imageimage

Nature of Nature of the the imageimage

At infinityAt infinity

Between Between infinity and infinity and optical optical centre O of centre O of the lensthe lens

At focus F1At focus F1

Between Between focus F1 focus F1 and optical and optical centre Ocentre O

Highly Highly diminished, diminished, point sizedpoint sized

DiminishedDiminished

Virtual Virtual and erectand erect

Virtual Virtual and and erect.erect.

Page 36: LIGHT : REFLECTION AND REFRACTION

POWER OF A LENSPOWER OF A LENS The power of a lens is a measure of the The power of a lens is a measure of the

degree of convergence or divergence of degree of convergence or divergence of light rays falling on it.light rays falling on it.

The power is defined as the reciprocal of The power is defined as the reciprocal of its focal length (f) as its focal length (f) as

P = 1/fP = 1/f The SI unit of power of a lens is dioptre The SI unit of power of a lens is dioptre

denoted by symbol D. denoted by symbol D. If f is expressed in metres so that 1 D= If f is expressed in metres so that 1 D=

1m1m-1-1

Page 37: LIGHT : REFLECTION AND REFRACTION

Human EyeHuman Eye

RetinaRetina PupilPupil IrisIris Aqueous humourAqueous humour Vitreous humourVitreous humour CorneaCornea LensLens Cilliary muscleCilliary muscle Suspensory Suspensory

ligamentligament

ChoroidChoroid Blind spotBlind spot Optic nerveOptic nerve foveafovea

Different parts of Human eye are as follows:-

Page 38: LIGHT : REFLECTION AND REFRACTION
Page 39: LIGHT : REFLECTION AND REFRACTION

SIMPLE MICROSCOPESIMPLE MICROSCOPE A simple microscope is a convex lens of A simple microscope is a convex lens of

short focal length. It is also called short focal length. It is also called magnifying lens.magnifying lens.

The convex lens is held near the object The convex lens is held near the object to be magnified, such that it is in to be magnified, such that it is in between the optical centre and principal between the optical centre and principal focus, but close to principal focus.focus, but close to principal focus.

An erect virtual and enlarged image An erect virtual and enlarged image A1B1 is formed at the least distance of A1B1 is formed at the least distance of distinct vision as shown in fig. Next distinct vision as shown in fig. Next page.page.

Page 40: LIGHT : REFLECTION AND REFRACTION
Page 41: LIGHT : REFLECTION AND REFRACTION

MagnificationMagnification

Size of the imageSize of the image M = Size of the object M = Size of the object = Distance of the image from eye= Distance of the image from eye Distance of object from eyeDistance of object from eye M = A1B1/AB = D/f ( because eye is held M = A1B1/AB = D/f ( because eye is held

close to lens) , Thus, if a convex lens of close to lens) , Thus, if a convex lens of focal length 6.25 cm is used its focal length 6.25 cm is used its magnification is magnification is

m = D/f = 25 cm/ 6.25 cm = 4m = D/f = 25 cm/ 6.25 cm = 4

Page 42: LIGHT : REFLECTION AND REFRACTION

COMPOUND MICROSCOPECOMPOUND MICROSCOPE

Construction – A compound Construction – A compound microscope consists of two metallic microscope consists of two metallic tubes such that they can easily slide tubes such that they can easily slide in one another. in one another.

The tubes are blackened from inside The tubes are blackened from inside to prevent any internal reflection.to prevent any internal reflection.

On the side of the smaller tube a On the side of the smaller tube a convex lens of very small focal convex lens of very small focal length called objective lens is fitted length called objective lens is fitted which faces towards the object.which faces towards the object.

Page 43: LIGHT : REFLECTION AND REFRACTION
Page 44: LIGHT : REFLECTION AND REFRACTION

On the side of bigger tube, On the side of bigger tube, another convex lens of larger focal another convex lens of larger focal length is fitted. This lens is called length is fitted. This lens is called eye lens.eye lens.

Working – A tiny object AB is Working – A tiny object AB is placed in between F0 and 2F0 of placed in between F0 and 2F0 of the objective lens, when it forms a the objective lens, when it forms a real, inverted and magnified real, inverted and magnified image A1B1 on the other side of image A1B1 on the other side of objective lens, i.e. within the objective lens, i.e. within the tubes.tubes.

Page 45: LIGHT : REFLECTION AND REFRACTION

Now the eye lens tube is moved Now the eye lens tube is moved backward or forward, such that the real backward or forward, such that the real image A1B1 falls between the principal image A1B1 falls between the principal focus (Fe) and its optical centre (O) of the focus (Fe) and its optical centre (O) of the eye lens. eye lens.

The rays starting from the real image The rays starting from the real image A1B1 on passing through the eye lens A1B1 on passing through the eye lens give rise to a divergent beam of light. give rise to a divergent beam of light.

When these divergent rays are received When these divergent rays are received by the eye, they appear to come from the by the eye, they appear to come from the points A2 and B2. points A2 and B2.

Thus A2B2 is the virtual, but highly Thus A2B2 is the virtual, but highly enlarged image of the object AB.enlarged image of the object AB.

Page 46: LIGHT : REFLECTION AND REFRACTION

The image formed here is inverted with The image formed here is inverted with respect to the object.respect to the object.

However, this does not make any However, this does not make any difference as most of the biological difference as most of the biological specimens seen under the microscope are specimens seen under the microscope are round and oval or not very well defined in round and oval or not very well defined in shape.shape.

Page 47: LIGHT : REFLECTION AND REFRACTION

magnificationmagnification

The magnifying power of a compound The magnifying power of a compound microscope is the ratio between the microscope is the ratio between the final size of the virtual image to the final size of the virtual image to the actual size of the object.actual size of the object.

M = (D x L) where D = least distance M = (D x L) where D = least distance of of

F0 x fe distinct vision, L= tube F0 x fe distinct vision, L= tube length, f0 = focal length of objective,length, f0 = focal length of objective,

fe = focal length of eyepiece.fe = focal length of eyepiece.

Page 48: LIGHT : REFLECTION AND REFRACTION

ASTRONOMICAL TELESCOPEASTRONOMICAL TELESCOPE

Astronomical telescope is an optical device Astronomical telescope is an optical device used to for seeing heavenly bodies such as used to for seeing heavenly bodies such as the stars, the Sun, the Moon, etc, closely.the stars, the Sun, the Moon, etc, closely.

Construction – It consists of two convex Construction – It consists of two convex lenses, i.e. an objective lens of very large lenses, i.e. an objective lens of very large focal length and eye lens of very small focal length and eye lens of very small focal length. focal length.

The two lenses are mounted on separate The two lenses are mounted on separate tubes which can slide in one another. tubes which can slide in one another.

Page 49: LIGHT : REFLECTION AND REFRACTION
Page 50: LIGHT : REFLECTION AND REFRACTION

workingworking

The rays coming from a distant heavenly The rays coming from a distant heavenly body are parallel to one another, but body are parallel to one another, but generally not parallel to the principal generally not parallel to the principal axis. axis.

These rays, on passing through the These rays, on passing through the objective lens, suffer refraction and objective lens, suffer refraction and hence, converge in the plane of the hence, converge in the plane of the principal focus to form a real, inverted principal focus to form a real, inverted and diminished image AB of a distant and diminished image AB of a distant body.body.

Page 51: LIGHT : REFLECTION AND REFRACTION

Now the eye lens tube is moved backward Now the eye lens tube is moved backward or forward so that the real image AB falls or forward so that the real image AB falls within the principal focus (fe) and the within the principal focus (fe) and the optical centre(O) of the eye lens. optical centre(O) of the eye lens.

The rays starting from the real image AB The rays starting from the real image AB on passing through the eye lens give rise on passing through the eye lens give rise to a divergent beam of light.to a divergent beam of light.

When this divergent beam reaches the eye When this divergent beam reaches the eye to it the rays appear to come from A1B1. to it the rays appear to come from A1B1. Thus, A1B1 is the final virtual and enlarged Thus, A1B1 is the final virtual and enlarged image formed.image formed.

Page 52: LIGHT : REFLECTION AND REFRACTION

Magnification Magnification

The ratio between the angle The ratio between the angle subtended by the final image on the subtended by the final image on the eye to the angle subtended by the eye to the angle subtended by the object on the unaided eye is called object on the unaided eye is called the magnifying power of telescope.the magnifying power of telescope.

m = fo/fe , fo – focal length of m = fo/fe , fo – focal length of objectiveobjective

fe – focal length of eye fe – focal length of eye lenslens

Page 53: LIGHT : REFLECTION AND REFRACTION
Page 54: LIGHT : REFLECTION AND REFRACTION

THANK THANK UU