chapter 10 geometric optics

8/19/2019 Chapter 10 Geometric Optics

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CHAPTER 10

GEOMETRICAL OPTICS

Contents:1. WHAT IS OPTICS?

2. TECHNECAL TERM DEFINITIONS.

3. PATH OF RAYS AND FORMATION OF IMAGE.

4. POSITON AND NATURE OF IMGE.

5. THIN LENS EQUATION AND MAGNIFICATION.

6. MAGNIFYING GLASS AND ITS MAGNIFYING POWER

7. COMPOUND MICROSCOPE.

8. TELESCOPE. AND IND9. EYE ANOTOMY

10. EQUATIONS

11. DIMENTIONS

12. SHORT DEFINATIONS

13. SUMMARY

14. SHORT QUESTIONS AND ANSWERS

What is OPTICS?Optics is the study of the behavior and properties of light including its interactions with matter and its detection byinstruments. Optics usually describes the behavior of visible ultraviolet and infrared light.

!"O#"T$IC OPTICS% In this branch of optics some simple laws are established on the basis of e&periments. Inthis branch light is supposed to travel in straight line path and reflection and refraction of light from materials is

studied.

P'(SIC)* OPTICS% In this branch the production and propagation and emission of light is studied. In this branchthe nature of light and related events li+e interference diffraction and polari,ation are studied.

TECHNECHAL TERM RELATI!E DEFINITIONS:

1. R"# o$ L%&'t:

*ight travels in a straight line from a light source. Thus the path of light can be represented by straight line. Thedirection can be shown by head arrow. The straight line along which the light travels is called ray of light.

(. )e"* o$ L%&'t:

) light source gives infinite rays of light energy simultaneously. ) group of rays whichtravel along a certain direction is called beam of light. The beam of light can be of thethree types% - convergent beam% ) beam whose all rays go to meet at a point. /0ivergent beam% If the rays of light starts from appoint and spread away from it. 1Parallel beam% If all the rays in a beam are parallel to each.

+. M%,,o,:

) mirror is an ob2ect with at least one polished and other reflective surface. The mostfamiliar mirror is the plane mirror which has a flat surface. Curved mirrors are also usedto produce magnified or diminished images or focus light or simply distort the reflectedimage. The image in a plane mirror is%

i. The same si,e as the ob2ect.

ii. The same distance behind the mirror as the ob2ect is in front.iii. *aterally invertediv. 3irtual 4it cannot be formed on a screen.

-. Lens:

) lens is an optical device with perfect a&is which transmits and refracts lightconverging or diverging the beam. ) spherical transparent medium made of glass or plastic that refracts light waves. Such medium is called 5*ens6. The lens can bringlight waves together or spread them apart. 'ence there are two types of lenses one of them is called 5conve& lens6 while the other is 5concave lens6.

. T'%n /ens:

It is a lens with a thic+ness 4distance along the optical a&is between the two surfaces of the lensThat isnegligible compared to the focal length of the lens. *enses whose thic+ness is not.

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http://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Optical_phenomenahttp://en.wikipedia.org/wiki/Matterhttp://en.wikipedia.org/wiki/Imaginghttp://en.wikipedia.org/wiki/Optical_instrumentshttp://en.wikipedia.org/wiki/Visible_lighthttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Plane_mirrorhttp://en.wikipedia.org/wiki/Curved_mirrorhttp://en.wikipedia.org/wiki/Magnificationhttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Axial_symmetryhttp://en.wikipedia.org/wiki/Transmittancehttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Lighthttp://www.answers.com/topic/lens-1http://www.answers.com/topic/optical-axishttp://www.answers.com/topic/negligiblehttp://www.answers.com/topic/focal-lengthhttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Optical_phenomenahttp://en.wikipedia.org/wiki/Matterhttp://en.wikipedia.org/wiki/Imaginghttp://en.wikipedia.org/wiki/Optical_instrumentshttp://en.wikipedia.org/wiki/Visible_lighthttp://en.wikipedia.org/wiki/Ultraviolethttp://en.wikipedia.org/wiki/Infraredhttp://en.wikipedia.org/wiki/Plane_mirrorhttp://en.wikipedia.org/wiki/Curved_mirrorhttp://en.wikipedia.org/wiki/Magnificationhttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Axial_symmetryhttp://en.wikipedia.org/wiki/Transmittancehttp://en.wikipedia.org/wiki/Refractionhttp://en.wikipedia.org/wiki/Lighthttp://www.answers.com/topic/lens-1http://www.answers.com/topic/optical-axishttp://www.answers.com/topic/negligiblehttp://www.answers.com/topic/focal-length


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. Cone2 /ens:

The lens is thic+er at the middle and thinner at the edges. Such lens is called 5Conve& lens6. ) conve& lens bringslight waves together. This type of lens is also called 0ouble7conve& lens.

) lens has one side plane while the other conve& is called Plano7conve& lens.) lens has one side concave while the other conve& is called Concavo7 conve& lens.

3. Con4"e /ens:

The lens is thinner in the middle and thic+er at the edges. Such lens is called

5concave lens6. ) concave lens spreads light waves apart. This type of lens isalso called 0ouble7concave lens. ) lens has one side plane while the other conve& is called Plano7concave lens. ) lens has one side concave while the other conve& is calledConve&o7 concave lens.

5. Po/e:

) midpoint of a lens surface is called 5pole6 or 5optical center.6

6. P,%n4%7"/ "2%s:

)n imaginary line that passes from a pole of a lens is called principal a&is.

10. Fo48s:) single point at which rays of light or other radiation converge or from which theyappear to diverge as after refraction or reflection in an optical system is called thefocus of a lens denoted by 5 8 6.

11. Fo4"/ /en&t':

The distance from the focal point of a lens or mirror to the surface of the mirror or the centre of the lens is called 5focal length6 denoted by 5f6.

1(. R"9%8s o$ 48,"t8,e:

The focal length of lens is half its 5radius of curvaturef

$ 9/

.

1+. O;e4t D%st"n4e:) distance from ob2ect placed to pole of a lens such distance is called 5ob2ectdistance6 denoted by 5p6.1-. I*"&e D%st"n4e:

) distance from image formed to pole of a lens such distance is called 5imagedistance6 denoted by 5:6.

1. A7e,t8,e:

In optics an aperture is a hole or an opening through which light travels. #orespecifically the aperture of an optical system is the opening that determines thecone angle of a bundle of rays that come to a focus in the image plane.

1. I*"&e:

If the rays of light starting from an ob2ect after reflection or refraction meet at appoint or appears to come from a point then this second point miscalled called image point of the first point. Thus the image of each point of theob2ect is formed. The images are of two types%

- REAL IMAGE: If the rays of light starting from a point after reflection or refraction actually meet atappoint then this point is called the real image point . Such image can be ta+en on the screen.

/ !IRTUAL IMAGE: If the rays of light starting froma point after reflection or refraction appear to comefrom second point then this point is called the virtualimage of the first point. Such image can not beformed on the screen.

13. PATH OF RAYS THROUGH CON!E< LENS:

%. )ny incident ray traveling parallel to the principal a&is of a converging lens will refract through the lensand passes through the focus on the opposite side of the lens.

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http://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Optical_systemhttp://en.wikipedia.org/wiki/Cone_anglehttp://en.wikipedia.org/wiki/Ray_(optics)http://en.wikipedia.org/wiki/Focus_(optics)http://en.wikipedia.org/wiki/Image_planehttp://en.wikipedia.org/wiki/Opticshttp://en.wikipedia.org/wiki/Lighthttp://en.wikipedia.org/wiki/Optical_systemhttp://en.wikipedia.org/wiki/Cone_anglehttp://en.wikipedia.org/wiki/Ray_(optics)http://en.wikipedia.org/wiki/Focus_(optics)http://en.wikipedia.org/wiki/Image_plane


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%%. )ny incident ray passing through the focus on the way to the lens will refract through the lens and travel parallel to the principal a&is.

%%%. )n incident ray which passes through the center of the lens will in effect continue in the same direction thatit had when it entered the lens.

15. FORMATION OF IMAGE THROUGH CON!E< LENS:

The image formed by a converging lens can be made using only three principalrays. Suppose an ob2ect ); is placed at a distance 5p6 from a pole of conve& lens.)ccording to the ray rules the rays from the ob2ect point ) are converge at a point)p>/f its image will be located

away from /8or 4:>/f.The nature of image will be real inverted and large insi,e.

. Suppose an ob2ect is on to 8 4p9f its image will be real inverted and very large

in si,e located at infinity or 4:9∞.

%. Suppose an ob2ect is between focus and pole of lens 4p


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;y comparing we getOOB IIB

9OP IP

IP IIB9

OP OOB

: IIB9

p OOB 7 7 7 7 7 7 7e:. 4-

Consider P8" and I8I< right angled triangles. ;oth triangles are similar Therefore8P

Tan 8 9P"

)nd8I

Tan 8 9IIB

;y comparing we get8P 8I

9P" IIB

IIB 8I 9

P" 8P 7 7 7 7 7 7 7e:. 4a

8rom the fig. OO< 9 P" 8P 9 f and 8I 9 4f :

Therefore( )f 7 :IIB

9OOB f

7 7 7 7 7 7 7 7 e:. 4/

;y comparing e:uation Ds - and / we get( )f 7 ::

9 p f

: f 9 p 4 f : : f 9 p f p :

0ivide by p : f both sides we get

: f P f p :

9 7 p : f p : f p : f

: f

p : f

p f 9

p : f

p : 7

p :

f

- - -

9 7 p : f

- - - 7 9 7 p p f

This e:uation is called 5concave lens e:uation6.

NOTE:

-. The ob2ect distance is positive for real ob2ects and negative for virtual ob2ects./. The image distance is positive for real images and negative for virtual images.1. The focal length is positive for conve& lens and negative for concave lens.

(. MAGNIFICATION:

#agnification is the process of enlarging something only in appearance not in physical si,e. This enlargement

is :uantified by a calculated number also called magnification. When this number is less than one it refers to areduction in si,e sometimes called magnification.

#athematically it is 5The ratio between si,es of image to the si,e of ob2ect6.

i

o

si,e of image 4 ' #agnification 9

si,e of ob2ect 4 '

i

o

' :#ag% 9 9

' p

+. MAGNIFYING GLASS:

The simple converging lens is called 5#agnifying glass6. It is used to see small ob2ects enlarge.

'ow large an ob2ect appears depends on the si,e of the image it ma+es on the retina of an eye. Thisdepends on the angle subtended by the ob2ect at the eye. )s an ob2ect bring up close to our eyes so that itsubtended a greater angle. 'owever our eyes can accommodate only up to a standard distance of /GH mmcalled 5least distance of distinct vision6 denoted by 5d6. The converging lens when acts as the magnifying glassthen virtual image which must be at least /G cm from an eye if the eye is to focus on it.

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. POWER OF LENS:

The reciprocal of focal length of a lens is called 5power of lens6 e&pressed in meter.-

Power of lens 9f

Its unit is 5diopter6 e&pressed in meter. Shorter the foal length greater the power of lens.. POWER ACCOMMODATION:

The ability of an eye to change the focal length of its lens so as to from a clear image of an ob2ect on its retina iscalled its 5power accommodation6.

3. DEFECTS OF LENS:

C',o*"t%4 "e,,"t%on:

The dispersion of light into its constituent colors gives rise a blurred imagewhich appears colored. This defect in the image is called 5Chromatic aberration6. ) lensacts li+e two prisms placed end to end. This gives rise to dispersion of light. Chromaticaberration can be removed by using a compound lens consisting of a conve& lens of onetype of glass and concave lens of dispersion. The conve& lens produces both deviationand dispersion. The concave lens minimi,ed the deviation and neutrali,es completely thedispersion. . Such a combination of lenses is called 5)chromatic lens6 4color correctedlens.

S7'e,%4"/ "e,,"t%on:

The rays which pass through a lens near its edges are brought to focuscloser to the lens as compared to the central rays. The image produced will not be

well defined and sharp. This defect in a lens is called 5Spherical aberration6. Thisdefect can be removed by using only the central portion of the lens. ) lens system thatis corrected spherical aberration chromatic aberration and other distortion is called an5)stigmatic lens6 whish is used in costly cameras and other optical instruments

5. COMPOUND MICROSCOPE:

Int,o984t%on:

Optical instrument used to increase the apparent si,e of an ob2ect It has multiple magnification. The compoundmicroscope was invented by !alileo in -M-H. The lenses with shortest focal length give the greatest magnificationand small ob2ects are seen enlarged.

Const,84t%on:

It consisted of an ob2ective lens and an eyepiece. The ob2ective of microscope is of smaller focal length f o andeyepiece has a greater focal length f e than the ob2ective 4f o> f e . ;oth lenses are +ept at the two ends of tube.

Wo,%n&:

) very small in si,e ob2ect is placed between the focus and twice the distance of the focal length of ob2ective sayvery close to the focal length p- ≅ f o . This lens forms an inverted magnified real image in front of eyepiece. Theeyepiece is so ad2usted that it forms a virtual magnified image of already inverted image say * ≅ :/. The eyepieceacts as the magnifying glass.

M"&n%$%4"t%on o$ 4o*7o8n9 *%4,os4o7e:

) compound microscope consists two converging lenses so that it has multiplemagnifying powers. 'ence #.P. 9 4#.Po 4 #. P. e

- /

- /o e

: :#.P.9

p p

o

* d#.P. 9 -E

f fe

;ecause eye piece acts as the magnifying glass.

)s larger the focal length of ob2ective than the smaller focal length of eyepiece the magnification will becomesvery shorter.

6. TELESCOPE:

Int,o984t%on:

) telescope is a device used to magnify distant ob2ects. )n ob2ect which isfar away viewed by an optical instrument +nown as 5Telescope6. Thefunction of a telescope is to increase the visual angle which a distant ob2ect

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appears to subtend at the eye and therefore produces the same effect as if the ob2ect were either larger or close to theeye. ) Telescope is used to magnify ob2ects that are very far away.

Const,84t%on:

) Telescope is used to magnify ob2ects that are very far away. It contains two converging lens located at oppositeends of a long tube. The lens closest to the ob2ect is called the 5ob2ective6 and a lens close to an eye is called5eyepiece6 which acts as a magnifier.There are number of +inds of telescope some of them are% )stronomicaltelescope reflecting telescope radio telescope !alilean telescope terrestrial telescope.

Ast,ono*%4"/ Te/es4o7e:

)n astronomical telescope used to see distant ob2ects li+e stars planets moon etc. which is effectively atinfinity. In refracting astronomical telescopes two conve& lenses are used. In this telescope only those rays from theob2ect which are bounded by the edges of the ob2ective lens enter the instrument. The lens acts as a stop to the lightfrom the ob2ect with a given ob2ective the best position of the eye is one where it collects as much light as possiblefrom that passing through the ob2ective.

Wo,%n&:

) converging lens of larger focal length which is used as the ob2ective lens f o .It will form the image of adistant ob2ect at infinity as close to the eye as we may desire. The image II< is real. )nother converging lens ofsmaller focal length f e 4 f o f e used as the eye piece near the image formed by ob2ective. The image I and focal planes of both lenses are in con2unction and the light coming out from the eyepiece is parallel. The final virtualerect and very large in si,e image I@ is at infinity by viewing eye. Thus the distance between two lenses is 4f oEf e for

an ob2ect at infinity.

M"&n%$%4"t%on o$ Te/es4o7e:

The magnifying power of a telescope is defined as the ratio between the angle subtended at the eye 4 β bythe final image and the angle subtended at eye 4 α by the ob2ect itself.

#agnifying power 9

J

-

Si,e of image OIJ 9

focal length of ob2ective : ;ecause f o ≅ :-

/

Si,e of image OI 9

focal length of eyepiece p ;ecause f e ≅ p/

e

o

OIf

#agnifying power 9OI

f

o

e

focal length of ob2ective f #agnifying power 9

focal length of eye piece f

8or !reater magnification the ob2ective have larger focal length and the eyepiece a shorter one.

GALILEAN TELESCOPE:

The scientist !alileo invented this optical instrument. The concave lens serves as the ocular lens or theeyepiece of small focal length of small focal length while the conve& lens serves as the ob2ective of large focallength and eyepiece. The lens is situated on either side of a tube such that the focal point of the ocular lens is thesame as the focal point for the ob2ective lens. The rays of light from a very distinct ob2ect fall parallel ma+ing asmall visual angle α with the a&is of the ob2ective and an inverted image is formed in its focal length plane. ;ut before he image is formed the eyepiece diverges the rays. The position of he concave lens is so ad2usted that theimage is within the focal length and therefore the virtual and enlarged image of the ob2ect is formed have largervisual angle β .The final image is upright with respect to ob2ect.

Thus

#agnifying power 9J

TERRESTRIAL TELESCOPE:

The construction and wor+ing of this telescope is same as theastronomical telescope. ;ut the only difference is that erecting lens of smaller

focal length is introduced between the ob2ectiveand eyepiece. The ob2ective forms a real inverted image of distinct ob2ectat its focus. This image is situated at distance twice the focal length of

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erecting lens. Thus this lens forms inverted and real image at the same distance to the other side of erecting lens.Thus final image is upright with respect to ob2ect. This image is formed with the focal length of eyepiecewhich forms its enlarged and virtual image.

10. ANATOMY OF THE EYE:

The human eye resembles cameras in its structure. The eye is an"nclosed volume into which light passes through a lens. ) diaphragmcalled the 5Iris6 4the colored part of an eye ad2usts automatically tocontrol the amount of light entering the eye.

The hole in the iris through which light passes 4the pupil is blac+

because no light is reflected from it and very little light is reflected bac+ outfrom the interior of the eye.

The $etina which plays the role of the film in camera is on the curvedrear surface. It consists of a comple& array of nerves and receptors +nownas rods and cons which act to change light energy into electrical signalsthat travel along the nerves.The reconstruction of the image from all these tiny receptors is done mainlythe brain. )t the center of the retina is a small area called the 8ovea about bo./G mm in diameter where the conesare very closely pac+ed and the sharpest image and best color discrimination are found?

Qnli+e a camera the eye contains no shutter. The e:uivalent operation is carried out by the nervous systemwhich analyses the signals to form image at the rate of about 1H per second.

The lens of the eye does little of the bending of light rays. #ost of the refraction is done at the front of the

cornea 4inde& of refraction 9 -.1NM which acts as a protective covering. The lens acts as a fine ad2ustment forfocusing at different distances. This is accomplished by the capillary muscles which change the curvature of thelens so that the focal length is changed. To focus on distant ob2ects the muscles are rela&ed and the lens is thin.When light from a distant ob2ect passes through the lens system of the eye it is refracted and brought to focus on heretina. There a real but inverted image of the ob2ects formed. While all retinal images are inverted they areinterpreted as being erect. To focus on nearby ob2ects the muscles contact causing the center of the lens to bethic+er thus shortening the focal length. This focusing ad2ustment is called accommodation.

The closest distance at which the eye can focus clearly is called the near point of the eye .8or young and adult itis /Gcm .) person


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Lon& s%&'te9 @H#7e, *et,o7%":

The disability of eye to form distinct images of nearby ob2ects on its retina is +nown as 'yper metropia

EQUATIONS

- - - -f p :

= +/

- /

- - -f f f

= +1 -

Power 9f

F d#.P of #.! 9 -E

f

G- /

- /o e

: :#agnifying power of compound microscope 9

p p

M o

e

f magnifying power of telescope 9

f

N *ength 94 : E p *ength of telescope 9 f e E f o

R dlinear magnifying power 9

p

-H

o e

* d#.P. 9 -E

f f

--

Iangular magnifying power 9

J

DIMENSIONS

KQ)LTIT(8O$#Q*) 0I#"LSIOL

QLIT

Ob2ect distanceImage distance8ocal length

P:f

* meter

#agnifying power magnification 0imensionless no unit

*ength of telescope * meter

Power of lens -f

*7- #eter 7- 90iopter

SHORT QUESTIONS

Q. B 1: W'# s'o8/9 t'e *"&n%$#%n& /ens 7/"4e9 4/ose to t'e e#e?

;ecause the virtual erect and enlarged image located at least distance of distinct vision by using magnifying glass.So that to see clear ob2ect the magnifying lens is placed close to an eye.

Q. B (: W'# s'o8/9 t'e o;e4t%e o$ 4o*7o8n9 *%4,os4o7e '"e s*"// $o4"/ /en&t'?

;ecause an ob2ect should placed be very closer to the focus of ob2ective to get real large and inverted imageformed close to the pole of eyepiece. 'ence the ob2ectives of compound microscopes have smaller focal length

Q. B +: Un9e, >'"t 4on9%t%on " 9o8/e 4one2 /ens "4ts "s " 9%e,&%n& /ens?

The condition under which double conve& lens acts as a diverging lens is when an ob2ect is placed with in the focallength say ob2ect distance less than focal length then double conve& lens is called diverging lens.

Q. B -: W'# %s 4one2 /ens o$ s*"// $o4"/ /en&t' 7,e$e,,e9 $o, " *"&n%$#%n& &/"ss?

;ecause a lens having smaller focal length greater magnifying power. We +now according e:uation thatd

#agnification 9 - Ef

. 'ence conve& lens of small focal length preferred for a magnifying glass

Q. B : D%st%n&8%s' et>een te/es4o7e "n9 4o*7o8n9 *%4,os4o7e.Te/es4o7e:

-. it is used to see far away ob2ects./. It is used to see ob2ects= whose visual angle is very small

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1. The final image at least distance of distinct vision or at infinityF. The image formed by ob2ective is small and real.G. The focal length of ob2ective is larger than eyepieceM. The final image should be smaller than ob2ect but visual angle increasesN. The eyepiece cannot act as the magnifying glass.. The length of instrument is f o E f e. R. The magnifying power is f o U f e .

Co*7o8n9 M%4,os4o7e:

-. It is used to see close ob2ects.

/. It is used to see small.1. The final mage will be at least distance of distinct vision.F. The image formed by ob2ective large and real.G. The focal length of ob2ective is smaller than eyepieceM. The final image should be virtual erect and magnified.N. "yepiece act as the magnifying glass. The length of instruments :- E p/R. The magnifying power is 4#.P.o 4#.P.e

Q. B : Ho> 4"n " ,e"/ %*"&e e 9%st%n&8%s'e9 $,o* " %,t8"/ %*"&e?

Re"/ %*"&e: !%,t8"/ %*"&e:

-. It can be pro2ected on to screen. -. It cannot pro2ect on to screen.

/. It is always inverted. /. It is always erect.1. This type of image is formed by the actual 1. This type of image is formed by not actualinteraction of reflected or refracted light rays interaction of reflected or refracted rays.

Q. B 3: E27/"%n >'# t'e /enses 8se9 %n e27ens%e o7t%4"/ 9e%4es ",e 4o*7ose9 o$ *o,e t'"n one 7",t?

The lenses used in the e&pensive devices are composed of more than one part only to remove lens defects. Theresults should be correct.

Q. B 5: W'# t'e *"&n%$#%n& /ens s'o8/9 7/"4e9 4/ose to t'e e#e?

;ecause the virtual erect and magnified image should be located at least distance of distinct vision. So that themagnifying lens should placed close to the eye

Q. B 6: W'en /%&'t ente,s &/"ss $,o* "%, %ts s7ee9 e4o*es /ess. Is %t 98e to 4'"n&e %n $,e=8en4# o,>"e/en&t'?

The speed of light in a medium depends on its wavelength. The decrease of speed is due to decrease of wave length.

Q. B 10: An o;e4t %s 7/"4e9 >%t' %n t'e $o4"/ /en&t' o$ 4one2 /ens. W'"t >%// e t'e n"t8,e o$ %*"&e?

When an ob2ect is placed with in the focal length of conve& lens then the nature of image will be virtual erect andmagnified.

Q. B11: W'"t %s t'e 9%$$e,en4e et>een G"/%/e"n te/es4o7e "n9 "st,ono*%4"/ te/es4o7e?

G"/%/e"n te/es4o7e: Ast,ono*%4"/ te/es4o7e:

-. In this telescope concave lens is used as the eyepiece. -. In this type of telescope conve& lens is used as eyepiece./. in this telescope erect final image formed /. In this telescope inverted final image formed

Q. B 1(: De$%ne %s8"/ "n&/e?

The visual angle is the angle subtended between an ob2ect and an eye or image and magnifying glass.

Q. B 1+: E27/"%n /%ne", *"&n%$%4"t%on?

The ratio between the si,es of image to the si,e of ob2ect is called linear magnification.height of image

#agnification 9height of ob2ect

Q. B 1-: W'"t ",e t'e 9e$e4ts o$ /enses?

There are two defects of lenses i spherical ii and chromatic aberration.

Q. B 1: W'e,e >%// e t'e %*"&e $o,*e9 %$ "n o;e4t %s 7/"4e9 et>een F "n9 (F o$ 4one2 /ens?

When an ob2ect is placed between 8 and /8 then the image will be formed away from /8. The nature of image will be real inverted and large in si,e.

Q. B 1: W'# s'o8/9 t'e e#e7%e4e o$ te/es4o7e '"e s*"// $o4"/ /en&t'?

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The eyepiece of telescope is used of smaller focal length. ;ecause in the telescope ob2ect is placed for away fromthe focus of ob2ective. Its real and small image formed close to the focus of eyepiece. The final image should beenlarged and virtual has larger visual angle. To get higher magnification have eyepiece of telescope have smallerfocal length eyepiece of telescope have small focal length.

Q. B13: W'"t %s /e"st 9%st"n4e o$ 9%st%n4t %s%on?

The minimum distance to see an ob2ect clearly is /Gcm called 5least distance of distinct vision6.

Q. B15: W'# >e 4o*%ne t>o o, *o,e t'"n t>o /enses?

Two or more lenses are combined to design an optical instrument. ;y this combination the power of lens also

increases. ;y this process we avoid lens defects.

Q. B 16: W'"t %s 7o>e, o$ 4one2 /ens >'ose $o4"/ /en&t' %s (04*?

We +now that-

power 9f

-Power9

/Hcm

-HHPower 9

/H meter .Thus Power 9 G 0iopter

Q. B(0: W'"t Is t'e Po>e, O$ A44o**o9"t%on o$ t'e E#e?

)ccommodation in the eye is the process by which the eye increases optical power to maintain a clear image on theretina.The focus of the eye is controlled by a number of factors including the iris cornea and muscle tissue that

alters the shape of the lens so that the eye can focus on both near and far ob2ects. Sometimes these muscles donBt wor+ properly because the eye is slightly altered in shape and as people agethe lens becomes harder and cannot be properly focused leading to poor vision.If the point of focus is short of the retina itBs +nown as VnearsightednessV which means that the eye cannot focus ondistant ob2ects. V8arsightednessV is where people have problems focusing on nearby ob2ects

Q. B (1: C"n #o8 see st",s # " 4o*7o8n9 *%4,os4o7e.

Lo it is not possible that e can see the stars by compound microscope. ;ecause eyepiece is of larger focal lengththan the ob2ective. So this is not possible.

Q. B ((: >'"t 9o #o8 8n9e,st"n9 # t'e 7o>e, o$ /ens? W,%te %ts 8n%t ot"%ns $o,*8/" $o, t'e 7o>e, o$ t>o

/enses 7/"4e9 %n 4ont"4t.

The reciprocal of focal length is called power of lens e&pressed in 0iopter.

-

Power of lens 9f

The unit of power of lens is 0iopter e&pressed in m7-.When two or more lenses are used in close combination that is with no space in between them the e:uation to

calculate the effective power of the combination is% combination- / 1

- - -Power 9 E E

f f f E7 7 7 7 7

Q. B (+: W'# %s " 4"n9/e $/"*e #e//o>?

The received color of an ob2ect is determined by the spectrum of its radiant flu& factored by the luminous efficacy of the human eye .If the human eye responded e:ually to all wavelengths in the visible range= the candle flame would

appear red. ;ut since the eye sensitivity pea+s in the green and diminishes toward the red wavelengths the eye perceives the color as yellow.

Q. B (-: >'# " 7%n 'o/e 7/"4e9 %n $,ont o$ " /ens /e"9s to " &oo9 %*"&e een >'en t'e %*"&e %s not =8%t %n

$o48s.

) pin hole placed in front of a lens reduces its aperture. The image is formed by the central rays. Thus we obtain agood image even of the lens is not in focus.

Q. B (: >'"t '"77ens >'en /%&'t '%ts t'e o;e4t?

When a light wave hits an ob2ect what happens to it depends on the energy of the light wave the natural fre:uencyat which electrons vibrate in the material and the strength with which the atoms in the material hold on to theirelectrons. ;ased on these three factors four different things can happen when light hits an ob2ect%

← The waves can be reflected or scattered off the ob2ect.← The waves can be absorbed by the ob2ect.← The waves can be refracted through the ob2ect.← The waves can pass through the ob2ect with no effect.

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)nd more than one of these possibilities can happen at once.

Q. B (: W'# s# see* to e /8e?

;ecause atmosphere is containing molecules of many different si,es including nitrogen o&ygen water vapor andvarious pollutants so that the "arthBs atmosphere is rough. This assortment scatters the higher energy light wavesthe ones we see as blue light. This is why the s+y loo+s blue.

Q. B (3: W'# $o4"/ /en&t' o$ 4one2 /ens %s *o,e $o, ,e9 4o/o, /%&'t?

;ecause when light possesses from conve& lens it bends to wads the normal. This coloured light has larger wavelength smaller fre:uency. So that focal length of conve& lens is more.

Q. B(5: T>o t'%n /enses ",e %n 4ont"4t. No> t'e# ",e se7","te9 "n9 7/"4e9 4o"2%"//#. W'"t >%// e t'e 7o>e,

o$ /ens 4o*%n"t%on?

When two thin lenses are in contact the power of lens combination increases. Low when they are separated and placed coa&ially the power of lens combination decreases.

Q. B (6: W'# 9oes s8n/%&'t 9,"%n 4o/o,?

The sunlight 4electromagnetic radiation chemically brea+s down dyes. Washing detergents and bleach do the samething. The e&act chemical formula of the dyes will ma+e a difference in how long the color lasts but nothing lastsforever. Sunlight carries ultraviolet 4Q3 light along with visual spectrum light. The Q3 light causes a chemical

reaction with color molecules and they fade over time.

Q. B +0: W'"t %s "n %*"&e?

In optics the li+eness or counterpart of an ob2ect produced when rays of light coming from that ob2ect are reflectedfrom a mirror or are refracted by a lens

Q. B +1: W'"t %s " %,t8"/ %*"&e?

On the other hand a virtual image occurs when the prolongations of the light rays converge to form an image butthe light rays themselves do not reach the point of convergence.

Q. B +(: W'"t %s " ,e"/ %*"&e?

) real image occurs when the rays of light from the ob2ect actually converge to form an image and can be seen on a

screen placed at the point of convergenceQ. B ++: >'"t >"e/en&t' o$ /%&'t >o8/9 #o8 ,e4o**en9e9 $o, 8se >%t' " *%4,os4o7e %$ t'e *"2%*8* 9et"%/

>"s to e seen.

The wavelength of light doesnBt limit magnification. It limits resolution. (ou can have magnifications that go far beyond the limits of resolution. In that situation things would loo+ larger but you would not see any more detail.Two factors limit resolution in a light microscope. The wavelength of light and the Lumerical )perture of the lenssystem. The shortest visible wavelength is FHH nm. The highest Lumerical )perture for a lens system to date is -.F.This means the best resolving power on a microscope is /HH nm.

QUESTIONS YOU HA!E TO FIND

K. D -% What is the use of spectrometer?

K. D /% What are the defects of vision? 'ow can these be corrected?

K. D 1% 'ow is the magnifying power of a a telescope b compound microscope affected by increasing the focallength of their ob2ective

K. D F% 0efine in short the construction wor+ing and magnifying power of a compound microscope?

K. D G% Show how the position nature and si,e of the image are formed by a conve& lens b concave lens.

K. D M% show that a real image of a man formed by a converging lens only inverts him but that he and his image stillhave the same right hand.

K. D N%if a telescope is focused on a moon and then directed towards a tree GHm away what ad2ustment would benecessary to focus the tree sharplyU

Prof: Najeeb Mughal, Composed by Tarvesh Kumar Page -1


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K. D % what are the different arrangements used for decreasing the length of terrestrial telescope.

Prof: Najeeb Mughal Composed by Tarvesh Kumar

chapter 10 geometric optics

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