Light final

1. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 1
LIGHT
CLASS X
STUDY MATERIAL & QUESTION BANK:
1. REFLECTION OF LIGHT:
The phenomenonof lightcomingbackintothe same mediumafteritstrikesasmoothsurface is called
reflection.
2. LAWS OF REFLECTION:
A. The angle of incidence andthe angle of reflection are equal.
B. The incidentray,the reflectedrayandthe normal to the surface at the pointof incidence are inthe same
plane.
3. PROPERTIES OF IMAGEFORMED BY PLANE MIRRORS:
A. A plane mirrorformsa virtual image
B. The image is erect
C. The image isof the same size as the object
D. The image islaterallyinverted.
4. SPHERICAL MIRROR:
It isa type of mirror inwhichthe reflectingsurface iscurved.
5. CENTRE OF CURVATURE:
It isthe centre of that sphere of whichmirrorisa part.
6. TYPES OF SPHERICAL MIRRORS:
A. Concave:It isa type of spherical mirrorinwhichreflectiontakesplace atthe surface onthe same side as
the centre of curvature.
B. Convex:Itisa type of spherical mirrorinwhichreflectiontakesplace atthe bulgedsurface.

2. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 2
7. IMPORTANT TERMS ASSOCIATED WITH SPHERICAL MIRRORS:
A. Pole (P):The centre of the reflectingsurface of the mirroriscalledpole.
B. Principal axis:The line joiningthe pole andcentre of curvature iscalledprincipal axis.
C. Principal focus(F):
concavemirror:
It is the pointonthe principal axisatwhichthe rays whichcome parallel toprincipal axis afterreflection
converge.
convex mirror:
It isthe pointonthe principal axisatwhichthe rays whichcome parallel toprincipal axisafterreflection
appearto diverge.
D. Radiusof curvature(R):
The distance betweenpoleandcentre of curvature iscalledradiusof curvature
E. Focal length:(f):
The distance betweenpoleandprincipal focusiscalledfocal length
F. Aperture:
The widthordiameterof the reflectingsurface iscalleditsaperture.
G. Relationbetweenradiusof curvature andfocal length:
Radiusof curvature is twice of itsfocal length.R = 2f or f = 𝑅/2
8. RULES FOR THE FORMATIONOF IMAGES:
A. A ray of lightwhichpassesparallel toprincipal axisafterreflectionfromaconcave mirror,passes
throughprincipal focus.
A ray of lightwhichpassesparallel toprincipal axisafterreflectionfromaconvex mirror,appeartodiverge
fromprincipal focus

3. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 3
B. A lightraypassingthroughprincipal focus,afterreflection,passesparallel toprincipal axis.
A lightray projectedtowardsthe principal focusof aconvex mirror,afterreflectionpassesparallel to
principal axis.
C. A ray of lightwhichstrikesatthe pole of a concave or a convex mirror,reflectsatthe same angle on the
otherside of principal axis.
D. A ray passingthroughthe centre of curvature of a concave mirror or directedinthe directionof the centre
of curvature of a convex mirror,afterreflection,isreflectedbackalongthe same path.

4. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 4
9. FORMATION OF IMAGESBY CONCAVEMIRROR FOR DIFFERENT POSITIONSOF OBJECT IN FRONT OF IT:
 CONCAVEMIRROR FORMS REAL IMAGESIN ALL THE CASES EXCEPT WHEN THE OBJECT IS PLACED BETWEEN
POLE AND PRINCIPALFOCUS.
 THE VIRTUAL IMAGE FORMED BY CONCAVEMIRROR WILL BE BIGGERIN SIZE THAN THE OBJECT.

5. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 5
10. FORMATION OF IMAGESBY CONVEX MIRROR FOR DIFFERENT POSITIONS OF OBJECT IN FRONT OF IT:
 CONVEXMIRROR ALWAYSFORMS VIRTUAL IMAGES
 THE SIZE OFVIRTUAL IMAGE FORMED BY A CONVEXMIRROR WILL BE SMALLER THAN THE OBJECT.
11. USES OF CONCAVEMIRROR:
A. Itis usedas a shavingmirror
B. It isusedin searchlightsandheadlightsof automobiles
C. It isusedby dentists.
12. USES OF A CONVEX MIRROR:
A. Itis usedas a rear viewmirrorinautomobiles
B. It isusedin apartmentstobringthe view of the cornerswhichare not directlyvisible.
13. MIRROR FORMULA ( used both for convexand concave mirrors)
1/f = 1/u + 1/v
Here u= objectdistance
v = image distance
f = focal length
14. MAGNIFICATION(m):
It isdefinedasthe ratioof size of the image to the size of the object
m = -v/u= h’
/h
 Magnificationisnegative forreal andinverted images
 Magnificationispositiveforvirtual images
 m= 1 for plane mirror.Itmeansthe size of the objectandthe image are same
 m >1, whenimage islargerthanthe object
 m < 1 whenimage issmallerthanthe object

6. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 6
15. SIGNCONVENTIONFOR SPHERICAL MIRRORS:
 All the measurementsmustbe done fromthe pole
 Measurementsdone inthe directionof lightare takenas positive
 Measurementsdone inthe oppositedirectionof lightare takenasnegative
Concave mirror Convexmirror
Objectdistance negative negative
Image distance Negative ( real images)
Positive ( virtual images)
Positive
Focal length Negative positive
Size of the object Positive positive
Size of the image Negative (real images)
Positive ( virtual images)
Positive
16. REFRACTION OF LIGHT:
The processof bendingof lightatthe surface of separatingtwomediawhenittravelsfromone medium
intothe otheris calledrefractionof light.
17. CAUSE OF REFRACTION:
Lighthas differentspeedsindifferentmedia.Therefore,itchangesitsdirectionwhen ittravelsfromone
mediumintothe other.
 It bendstowards the normal whenit travels from rarer to densermedium.
 It bendsaway from the normal whenit travels from denserto rarer medium.
18. LAWS OF REFRACTION:
1. The incidentray,refractedrayand the normal lie inthe same plane.
2. The ratioof sine of angle of incidence tothe sine of angle of refractionforthe same pairof media
remainsconstant. ThisiscalledSnell’slaw of refraction.
19. 𝐒𝐍𝐄𝐋𝐋’𝐒 𝐋𝐀𝐖 𝐎𝐅 𝐑𝐄𝐅𝐑𝐀𝐂𝐓𝐈𝐎𝐍:
The ratio of sine of angle of incidence tothe sine of angle of refractionforthe same pairof mediaremains
constant.Thisis calledSnell’slawof refraction.
The constant iscalledthe refractive indexforthe pairof the media.
𝜇2
1
=
𝜇2
𝜇1
=
𝑆𝑖𝑛 𝑖
𝑆𝑖𝑛 𝑟
20. REFRACTIVE INDEX:
The ratio of sine of angle of incidence tothe sine of angle of refractioniscalledrefractive index forthe
givenpairof media.
𝜇2
1
=
𝜇2
𝜇1
=
𝑆𝑖𝑛 𝑖
𝑆𝑖𝑛 𝑟
(OR)
The ratio of speedof light inthe firstmediumtothe speedof lightinthe secondmediumiscalled
refractive index of the secondmediumwithrespecttothe firstmedium.
𝜇2
1
=
𝜇2
𝜇1
=
𝑆𝑖𝑛 𝑖
𝑆𝑖𝑛 𝑟
=
𝑣1
𝑣 2

7. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 7
21. ABSOLUTE REFRACTIVE INDEX:
The ratio of the speedof lightinair (vacuum) tothe speedof lightinthe givenmediumiscalledthe
absolute refractive indexof the givenmedium.
𝝁𝒎𝒆𝒅𝒊𝒖𝒎=
𝒄
𝒗𝒎𝒆𝒅𝒊𝒖𝒎
;
here c isthe speedof lightin air (vacuum)
22. OPTICAL DENSITY & MASS DENSITY:
The abilityof the mediumto refractthe lightwhenpassesthroughitiscalledoptical density.
Mass per unitvolume of asubstance isknownas itsmass density.
Kerosene hashigheroptical densitythanwaterbutitsmassdensityislessthanthatof water.
23. REFRACTIVE INDEX OF WATER IS 1.33. WHAT DOES IT MEAN?
The ratio of speedof lightinair to speedof lightinwateris1.33
24. REFRACTION OF LIGHT THROUGH A GLASSSLAB:
EO = Incidentray i1 = angle of incidence
OO1
= refractedray r1 = angle of refraction
O1
H = emergentray r2 = angle of emergence
 The extentof bendingatthe opposite facesof the glassslabisequal andopposite.Thatisthe reason;
the emergentrayisparallel toincidentray.
 The perpendiculardistancebetweenthe emergentrayandthe original un deviatedincidentray(inthe
absence of glassslab) iscalled‘lateral shift’.

8. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 8
25. REFRACTION BY SPHERICAL LENSES:
Lens:
A transparentmaterial boundedbytwosurfacesof whichat leastone iscurvedisa calledalens.
Convex lens:
A lensthatis thickeratthe middle thanatthe edgesiscalleda convex lens
Concave lens:
A lensthatis thickeratthe edgesthanat the middle iscalledaconcave lens
26. IMPORTANT TERMS RELATED TO SPHERICAL LENSES:
A. Opticcentre:
The central pointof the lensiscalled Opticcentre.A ray of lightincidentatthe opticcentre passesalmost
withoutanydeviation.
B. Principal focus:
A setof raysparallel toprincipal axis,afterrefractionfromone of the surfaces,converge orappeartodiverge
froma pointonthe principal axis.Thispointiscalledprincipal focus.
C. Focal length:
The distance of the principal focusfrom the opticcentre iscalledfocal length.
27. RULES FOR THE FORMATIONOF IMAGES IN CASE OF SPHERICAL LENSES:
A. A ray of lightpassingparallel to principal axis,afterrefraction,passesthroughprincipal focusonthe other
side of the lens. (FORCONVEX LENS)
A ray of lightpassingparallel toprincipal axis,afterrefraction,appeartodiverge fromthe principal focus
on the same side of the object. (FOR CONCAVELENS)

9. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 9
B. A ray of lightpassingthrougha principal focus,afterrefractionfromaconvex lens,willemergeparallel to
the principal axis.
A ray of lightappearingtomeetat the principal focusof a concave lens,afterrefraction,willemerge
parallel tothe principal axis.
C. A ray of lightpassingthroughthe optical centre of a lenswill emerge withoutanydeviation.
28. FORMATION OF IMAGESBY SPHERICAL LENSES:
A. Objectat infinity Image isreal,pointsized

10. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 10
B. Objectbeyond2F image isreal,inverted&smallerthanobject
C. Objectat 2F image isreal,inverted&same size asthe object
D. ObjectbetweenF&2F: Image isreal,inverted&biggerinsize as the object
E. Objectat F
Image real,inverted&isinfinitelylarge

11. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 11
F. ObjectbetweenF&O:
Image isvirtual,erect& large
 A CONVEXLENS FORMS REAL IMAGES IN ALL THE POSITIONSOFTHE OBJECT INFRONTOFIT EXCEPT WHEN
IT IS PLACEDBETWEEN PRINCIPALFOCUSANDOPTICCENTRE.
29. FORMATION OF IMAGESBY A CONCAVE LENS:
 A CONCAVELENSALWAYSFORMS VIRTUAL,ERECT & SMALLER IMAGES.
28. LENS FORMULA:
1
𝑓
=
1
𝑣
+
1
𝑢
Here:u= objectdistance;v=image distance;f = focal length
30. MAGNIFICATION:
It isdefined asthe ratioof size of the image to size of the object
m =
ℎ
ℎ1
=
𝑣
𝑢
 FOR CONCAVELENS‘m’IS ALWAYSPOSITIVE
 FOR CONVEXLENS‘m’IS NEGATIVEFOR REAL IMAGES AND POSITIVEFORVITUALIMAGES.

12. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 12
31. SIGNCONVENTION:
ConvexLens Concave Lens
Objectdistance negative negative
Image distance Positive (real images)
Negative (virtual images)
negative
Focal length positive negative
Size of the object positive positive
Size of the image Negative (real images)
Positive (virtual images)
positive
32. POWER OF A LENS:
The abilityof a lenstoconverge or diverge the raysof lightiscalleditspower.Itis definedasthe reciprocal
of itsfocal lengthwhenexpressedinmeters.
P=
1
𝑓
S.Iunit: Dioptre
Def of1Dioptre:
The powerof a lens issaidto be 1 dioptre whenitsfocal lengthis1 metre.
 THE POWER OFA CONVERGING( CONVEX) LENSIS POSITIVE
 THE POWER OFA DIVERGING(CONCAVE) LENSISNEGATIVE
33. COMBINATIONOF LENSES:
Whentwo or more lensesare incontact:
The resultantpoweris; P = P1 + P2 + …..
The resultantfocal length;
1
𝐹
=
1
f1
+
1
f2
+ ⋯
QUESTION BANK: (Know the answers from your teacher)
1. A concave mirrorof focal lengthf can form a magnified,erectaswell asinvertedimage of anobject
placedinfrontof it.Justifythisstatementstatingthe positionof the objectwithrespecttothe mirrorin
each case for obtainingthese images.
2. Distinguishbetweenareal andvirtual image of an object.Whattype of image isformedi) bya plane
mirrorii) on a cinemascreen
3. What isthe minimumnumberof raysrequiredforlocatingthe image formedbyaconcave mirrorfor an
object?Drawa ray diagramto show the formationof a virtual image bya concave mirror.
4. Explainwiththe helpof adiagram,whya pencil partlyimmersedinwaterappearstobe bentat the water
surface.
5. Withthe helpof a ray diagramexplainwhyaconvex mirrorispreferredforrearview mirrorsinmotor
cars
6. One half of a convex lensof focal length20 cm iscoveredwitha blackpaper.
I) will the lensproduce acomplete image of the object?

13. Prepared by E.V.Ramana, PGT (Phy), KV CRPF, Hyderabad. Page 13
Ii) Showthe formationof image of an objectplacedat 2F of suchcoveredlenswiththe helpof aray
diagram
Iii) Howwill the intensityof the image formedbyhalf-coveredlenscompare withnon-coveredlens?
7. Explainwhywe see the sign
in frontof some vehicles?
8. A ray of lightisincidentonthe plane mirrornormally.Whatare the angle of incidence andthe angle of
reflection?
9. Withthe helpof a ray diagramshow that angle of incidence isequal tothe angle of reflectionwhen aray
isincidentonthe concave mirror.
10. Discussthe positionandnature of the image formedbya concave mirrorwhenthe objectismovedfrom
infinitytowardsthe pole of the mirror?
11. Why doesa ray of lightpassingthroughthe centre of curvature of a concave mirror afterreflectionis
reflectedbackalongthe same path?
12. A pencil partlyimmersedinwaterinaglass tumblerappearstobe displacedatthe interface of airand
water.Name the phenomenonof lightresponsible forit?
13. Name twospherical mirrors. Define them.Write anythree pointsof difference betweenthem.
14. The magnificationproducedbyaconcave mirroris m= + 4. Write the informationaboutthe image given
by thisstatement.
15. Withthe helpof a ray diagramexplainthe use of concave mirroras solarconcentrators
16. A thinconverginglensformsa:1) real magnifiedimage2) virtual magnifiedimage of anobjectplacedin
frontof it.Write the positionsof the objectsineachcase.Draw labelledraydiagramstoshowthe image
formationineachcase.
17. How will the followingbe affectedoncuttingthe convex lensintotwohalvesalongthe principal axis?
1) Focal lengthii) intensityof the image formedbyhalf lens.
18. For whatpositionof the objectdoesa concave mirrorform a real,invertedanddiminishedimage of the
object?Drawthe ray diagram.
19. What lenscan be usedas a magnifyingglass?Forwhichpositionof the objectdoesaconvex lensform:
i) a virtual and erectimage?
Ii) a real and invertedimage of same size asthatof the object?Draw labelledraydiagramstoshowthe
formationof the requiredimage ineachof the above twocases.
20. How will youidentifywhetheragivenlensisconcave orconvex withouttouchingit?Alsomentionone
use of eachof the lens.
NUEMRICALS:
 Practice NCERT textbookexamplesandexercise numericals.