CHAPTER

HUMAN
EYEAND
COLOURFUL
WORLD

:
:
In t his chapter you will study ... .............
Refraction of light through prism, Dispersion of light, Scatter- :'
Ing oflight, Flln,;rioning oflnls in human "II•, IH!fects of vision, :
:'
I ict of Tapio
Topi.c.-1: Human Eye,
Defects ol V«loo and
Corrections
! Correcting de/eds ofvision. Applu::at:iDn of spherical mirrors and : Pav- No. 247
I tenses : Topi.c-2 : Refraction
'
·---------------------------------------------- --------·' or ligh t through prism,
Dispersion o f Light and
Scattering of light
Pa,e No.251

Human eye, Defects of vision and its corrections

Topic-1 Com:epta Cawwnd • BWl'Uffl • ~ • De/P.et. of nrit.-1 und Ua Corn'A:tt.on..-.

EP Reviaioll Notes
lfum~n Eyt • l'vpU : It Is th< Window of th• eye. It is the central
► E)'i' ls a natural optical dPViC:P uJ!rig which hunun .apttlure, In Iris, Tl regufates ,1nd C'Ontmls th-t amount
C'Ollld see obje-(1$ itt0l1nd him. ft kmns an lnv~rted, of light euteru,g the eye.
real in:ia~ on a light sensitive .surface: ca.lled retina. ► Retina : It i$ a ddi,catc tttentbr.u\C having cnonuous
... Row and cones a~ the cclJs in rcti11a. which are number of light 5ensltlve ct-lls.
light s.:nsitivc. Rods n-spond to the :int ensity of lighL ► CUi.ary musdes : These muscles change the shape
Cones respond to the Wumln1Jion of rolours. and .slU' of the eye lens fur focussing,
Thttt att around 125 million rods and coots ~Us. ► far point : The maxbnum dJ&tanre at which obj«{
l'ht c:ell1 gn\erate siglWS which are trai'lsmitted. to can beSPPn de.arty is far point ol thf' eye. For a norm.a.I
U.e brain through optiC: nen>e.. adult eye. Its value is infinity.
Parts of Human Eye
► Com-ta : It h th, outttrnost, transparent part, ft @=<;.? Keywords
provides OlOSt o/ the refr•ctlon of light, : Optlbl~ Reh1t1,., g ,. sigh•.
► t,,u : It is composed oh fibrous, jelly like malffl3!. It ,
provides I.he focused. real and inv-c".rtcd im.ag:e of the : Illumination:1b rna.ke sh.in.irtg or luntinous. ,
object on the retina. Tilis ronvmc lens con"'e-rges light ► ···••~········ ·······························
Optic Nt:rv't : The optic ni:rvc sends the do:triotl
al retina..
► Iris: ll is a dark muscular diaphragm thal conlrols lhe
Impulses from. the retina, •t the back of the eyes to
th, brain.
size of the pupa.
a O wwH.I CBSE Que•lion R• n.k Cha1,1erwiae &, Toplcwiae, BCIJ:llfCB, CIH••X
I
IJ; ; ~\I
Ii :
iii j<
i!i
..
.!5(
i \ [!1:liiI .. .. J II

11 \
i ll 'g
11llli
. ..

i' -
I

I !
j •

# ~
l~ :,,
~ ,,.
·1
··
,
· ... Q,
•
I HUMAN KYE ANO COI..OUN.>'1..11. WONlJl Im
► Nt:ar po(nl or 1.,t.ut dlttanrt o( dlttln<I vl1lon Myopia (NeaulghttdMM) ,
~ mlutmum dblDJU.'t at whk'h obfc:rtl c11n bt ..:eon • 0!1111111 obJ«tJ 1111-r. 110 1 de•r1y vl!Ubht,
n,0111 dl,111\t'llv,-ly WllhO!.JI Alr"ln.
P.uolM uy, frllm
• flor • oonnal iaduh eye, ltt v1l~ ii 25 <m . Jl•lnnt {lhlC!CI
• Rango o( human vltM>n it 25 cm to ln/inity, (,11 inOnity)
► Attommod.lUon: Tot 1blllly of lht eyt ltn1 10 AdJ1itl
1111 foe.ti length 1, e.i1Utd •«ommodation. Focal lt1\gl.h lmaxl'i:•
Ciln be clumgl.'d with the bclp of d.1iary mulclcs. form«I in
Strurtun! o! ffl Hwrun Eye: rn-.n1 " '
lh\.•retina
Vih·eous humor
Olwy ► fn , myopk ~. Image of dbt.mt obfect ls formed In
muscles &ont of th~ retina. (and not on d1c rttina)

•
f -..: _ -+
f;ir IK•lol or - ' lmn~c I~
lht• ' ')'l' form,.'d on
lht n:thrn

Aqm.'VuS hu1U4.tr
~
► Tho fu point (f) of a myopic eye iJ le,. than lnfinJty. ~~
liN
K,1)'11 ;,1 rt'
...
SbYcture .r

Jlvt•rt;t-d b,v
r.-r.,U~I my11 frnm
. I
1h.,lm1I libjt-c·I

... .
(111 ln fiult)')

p. ,. :~
( On(IIV\' 11:n.!i

1
- - "'"'....t ~ .... lm11i;,1 i• t,1m1,:J
Vin u11I lm.ai;r In frllMI uf
(11,ml.'d .,, P 1lu i r1.'1ln4
Conl-J \'l' ll•n,- lo
C'u rn-c:I n'l)upln

► Correction : Th.e concave lens placed in honr or the sec nearby objects dearly.
eye !onus a vlmlill lmagt ol dls!Anl ol>je« at far point t> The near polnl of lhe eye '"""'5· •w•y ln,01 25 en.
(F) of myopic tyc. ► Image Is fom1<d behh1d the r,ijna.
Hypum"'"1pia (Fusigl,t,dnu5): ► Corrtttion: Use of convtx lens of 1ult.ANe power can
► Affech>d Jlf'fM)4li c.an ,ee fu obt«tt C'leMly but C'.itnnot corn"'CI this dt'(t.'d..

___ ___. - ..,,,.

Nmnrnl l(yu
!Sharp lmt1~l' ol
1.lhj1.'4:t 111 N
(11,., polntJI
m O•w•nl C U.Sit Que11tlon B• n.lc Ch• pll!IWl•r & Tbplcwln. ICl:llNOI, CIH• X
I
- , ~twp,,-n11•1n, •lrf.y,,
!Rlurn.:-d im,,~ of nbj1."CI .11
N (m:..u pl>int)
i harp im,1ge of obj"d at NI

l
I lype rmPlmpir' l!yt'
(!-harp Image of
object at N)
j
l'r,obyopla COid ago Hypcrmttropl.al:
> ll i~ the d efccl of visk,n due lo which an old l'ffl'Wll cannot SE!I! the ne.arby objects c!Nrly due lo l11ss power o(
t«ommodfttlon o( thr ~ •
► The 1wa.r-polnt of old pcmo hiavll\g prnbyop,11 gnduo.lly n........-d.1."1 and b«'Omc, niuc.h moni th.an ZS au,

0B..JECTIVE TYPE QUESTIONS ( 1 morltvach)

F.xplanalWM : Light rays rell«tlng from distant

A Multipl e Choice Questions objects att focussed on the retina alter they passed
through the comea. aqueous h.un\OU.r, the It'll!, and
Q. 1. Whf'n Wf' enle1' .a d.arlc roc,m romlng fmm otatJide, ftnillly the vltttoos hun\Our, Most of the refraction
lm""dl.a-ttly the lhlng& ln1ldit the room do not of light ocn,rs wh~n the dlHerenc:, In tilt ttfrM"tivf'
•ppeu clfo.;u lo our">'"· Thit ia bt!c,uR lndffl of ttblllting mtdJ,i ls th~ ~lllfft.
{A) pupi11 do lllM opl!n , i all In lhl'I d.i.rk. A II.It uf Rcfr11cuw lndlcd Of v&rlou.i componc:ntt of
(8) pu1riltt•k• tlm• to adlutt. the hun'-'n ~ :
tC) Ught tr,we-11 llowtt In a dark room. s . Nn, I l\1rdlmn I Hf'ff.1rltv.- lru l ni
40) pupil• upcn Vf!!Y quidtly Ln the dark.
(I) Air 1.000
m
(CB~f SQ!\ 2Glf1
(ll) 1,376
Ano. Opllon (D) 11 ..,.,,...,, Cornt&
£ql11m1Non: Whcll we enter a d.arlc. room a:utti.ng (ill) Aqueous h umour 1.336
from oumidc. inunrdiiltr:Jy the things il1Si.dc the (iv) lens l 42
roontdol\Otipptardea.r toourey,s.. ThJ&is b«ause
pupn5 t11kt- tlm~ to 11dJui t.
Q. :Z. Th• ph<110....,. of light rnpun&lbl• for 1hr
1 M
- ViJroous h umour
--
Q. 4, Tht foc ll length of tht tyf l tn.1 lnatHH when
1.336

WO'l'liclng ol th., hum.an fl)'t It ...,. fflYKIH

(A) r<llcctlon (A) an, r<14Xcd and 10111 b«v11101 thlrnui,.
tU> ~fr11ctkm (II) Ml\lr,,c:t .1md Wn1 l>«t,RU! thktu!r.
(C) pnwtr ol 11C'L'YlmmM.111~n (q an, l'i'!lAxed ,md len, befflrru,, thlebr,
(D) p,nl11,nc,, o(vt,lnn (?;m (COSF SQr, lGII) (0) t."01\tract al\d i.en, b«omt thinner,
Q, 3. When Ught ra)'I enter lht eye, mOdl of th.t ,mac- ~ W [>IClcKI' bc<mplnl
tlon O<t'ur& i t lht Q. S. A pu'fiiOn C".ln.Ml see dlJllnc:tly objttb bpi beyond
(A) ay,talline lens. 2m. This d~fl'd cm btt cornd!l'd by using .t kns ot
( 8 t outer surhw:e of the cornea. powu
(C) Iris. (A) + 0.5 D. f81 --0.5 0.
(D) pupll. m 1><CFRTEu111pla,J (Q +0,2D. (D) --0.2 o.
Ant. OpUon (I) 11 ronwl, r.l'!I INl 1<11 I lH m rw I
I
Ans. Option (81 is a,med.
HUMAN EYE ANO COLOURF\lt.. WORLD -

Q. 2, AsHrtion (A) : A hypc:m,ctroplc per.son pre-fen to

Uplll.Nutin,, : This person is su,,ering lrom myopia remove hiJ spectacles, while drlving.
a nd nfl'f'(l,-' cone-A~ k>ni. tdnC'P, powt>r of lhP lem Rel90<l (R): When a hypennetropk ptT!()II wearing
wouJd be negative. the spectacles looks a t a dislant oo;e,...;. the parallel
rays from the dista.nl obterl get converged in &out
P• , •
l l or the rellna. 11u- ln,age lhuJ •p~an blurred. tlJ
2(m) • OJD An• . Option (A) I• co,rtt1.
Q, 6. Tht hum.1n ~ tin (nc'11.1 objfC'fl .at dJ(ftttnt &,,JAnatlo,, : Whf'I\ A hyperm~tropic p'1Mln wear•
cfutmus by ,1,dju.sling thr focal length or lhe eye ing thi: 1})1-"Ctadc» look» at ll dbtant objca. the par•
allcl rays front the dlnant obfect get converged bt
lllM, Thi• ii due to
front o( the retin.t. The image appears blu.rrcd, in
(A) prt1byopla. (8) acrommod1tlon. <n'det l6 iVo!d tlw, llw pmol\ p n!ferl 10 m\\<lVe !Ji
(C> n,anlght..in.... (D> farslghttdne11. spectadn.
mINC.UH b.<mplar) Q. J . A>lfrtion (Al I Conave ''"' I! ultd 11> corrttt myopU
Of 1hort-iightcdne51,.
Anl. Opl km fB) lt l'ON'f'<"l.
Re.uon (R) 1 A concave Lens of suitAbl'-' (ocaJ length
Cxpl;1utb, : Hwnan t)'t tar\ c.h11ngr thr rocaJ
div~ the parallel r,1y1 from the dbWn objcctl ;u
length of the eye len, to 1tt the objects 1ltuattd at If tht.y ..,,. coming tmm thP. (a r. point o( 1M inyork
Vlltktu.J dhuuww from tht. qt, Thl111 poulblt" dut eye. Thi• help• the C)''-' hms lo lonn a dear lu1.1gc 111
to the poWl"r o( 11tt0mn\odatlon ol thci e~ lenr.. thtrtdn.a.. m
Anll, Option (A) It COr N'd.
B Asa•rtlon 6 Reason &,J/JIMlkm : A (OnC,W f ltnt of tultablf fot':111 ltngth
diVl"fl51.'S Ille piUUlld fllY• /rum th~ dht.Anl ob"'-"Ct• a~
Oirfdion1 1 In the foUoWffll cptt-UtJn" A lf they ire l'01utng from tht fu potnt o( the myopk'
11,11,n,,.111 of. Al tf!t1•on tA} It (a11oWf'd by ,1 eye. Thi• he1lp1 tlw- eyt' i.tl\1 to lonn II clt'11r l.11\Atp! al
the rc-Un11. So, a com:avc W1u ued to«:o~ myopw
...
11.alemtnt of It.t»on (R), ~rk the corrN:t choice or 1ho,Mltht111dtw>M,
Q . , . A1..r1Jon (A) , Llgl,1 rmm • d:l•1•n1 obi""' •rrlvlng
(A) Holh (A) •n<I (R) arc true 411d (R) i, Ow eorrc<t at tht eyt lt.n, may g,tt tonwrgtd 111 a point In fronl
""Pi4f••~OII <>i (A). o{ the rf'llna.
01) both (A) and (RJ an: tru<' but R 11 NOT dtt' currt:i:t t\euon (R) ; The eye Ii productng tOO much
"'pl.rnaHon o,f (A). dh¥1'8tmtfl h\ thf' hldd,n1 bt.1m. ID
(Q (A) It true but (R) 1, laltt.
A•••OJ»lon (0 I• torTf<t,
bpJ1t,uetlv11 : The light from III dlJU.lll CJibicct arriv•
(DI (A) b f•loe and (R) b true. b~ ,t the eye lt ns may 1'ltt coi:w ~rgtd ot I point In
Q. J. AAMtrtlon CA ► 1 Ey, lttU h,u 1ht 1bllity to (oru.J front of the: n:dl\l, Th.It type of dc:f«t l1c11Jed near•
d~arly on lh• n,,llu,, by adjuaUng u, focal leng1h. tl,ghtt!dntH or myOl)IA, Thi• m,11ns th.At the tff' It
Ru1on {R) : Thia ph•nom•non 111 known "" powt.r produdng 100 much c:01wergit11tt In 11~ lnddtnl
o( a«om1m>druion. ~ m beam.

SUBJECTIVE TYPE QUESTIONS

Ano, (I) Pupil, (U) RctillA, )It )I
· <®> Very Short Answer Type Q. 6. Wh.11 ll thl" n,Hun of th• lnuge formed on lh~
Oue1tion1 (1 marl:eachl , ,tin,,! GI] Ill
Q. 1. S talf' nnt funrlinn ol lrl11 In hum.an t'fl", Am. Rn~ inverted and d.iminUhed in lizl!. l
4:)l!l (Cll~F SPI A· l. ?OU) Q, 7, A Pf™"• la ,dvblf11 lo wu r •pt<1Mlt11 wllh coo·
Q. 2. N&ttU" lhe p.ul of lhll bum•n t!)'I! llwl helps tn vn l l!MH, Sl• te.lhl! dd«I o(vision he la au.(Il!fi.ng
t.hangJng the rnc.aJ lmgth of lhe eye lei.¥, lrom. l!I IC'U~E Stt 8 ·1. 2011 )
1!J [C.'8SE S.I A•I, lll l IJ AN. The pcnc>n ls suffering from hypcmu:tropia. 1
Ans.. Cilia.,y mutcles. I
Q. 3. What it lht nngr of vWun of • nomuJ. human
<Y< l ~ fiTil l!J/ Cl!SE SPI A· l 2011)
CJ. 4. Wh..at I• tht fu.nctlon o(p'upH n hunun eyt.? £ Commonly Made Error
Cf) l!I (CBSF S-1 A· I, 21111 I
Q . !. Name the p&.r!l of lhe eye: • ► Studmts u.sually get ronfuxd ~tween myopia ;
(i) Controls 1hr ill.mount of lighl mtuing into the: eye. and hYJ>fffi~h'Opla. They write lnoorrect :
(II) FormJ rtal, Jn-vtrtt.d lmagt or tht obj«t fcmntd on answer:. :
11. l!I f<BSF ~•• A-1, 2011!
ml UIIW••d CHS~ QueaUon H• .n.k ClmJ>lcr'Wlae & Tnplt.'Wl•f!, ICl:RNC&, Cina X
I
Ant, Given.
-:(&): Answering Tip Obj«t dlJtan(t, 11 • -25 ~\
lmi1gt, dl11J11~, 11 • -..,0 r.m
l ► Undcntand lhe con.:rpt o{ myopia aru:I : Focal length../ • 1
Using lens 11lnnula.
: hypermel1"0pl• wllh proper ray dlagr•m. ;
.-- ------- ----------------------. -----------. .!. • .!. _.!.
f ••
<@) Sh0rtAnav.rerTyp1t I 1
Oue ■tlcn■ -1 (l! nuub oacl,) ----
-50 -25
Q.1. Dffino lh• 11nn powor of ""'mmod.otlno. w,11,
tht modJIICltfOn ln tht ('Ut\'lhlff'
lenJ which e:n1ble1 LI.I lo ltt the
ol tht,y,
nt11rby obj«ul
---50I •-25I
....,ty 1 (?)l!J 1c usn,.,lbl Sfl '· lOlftJ _-1 •2 • .!.
Q .1. Write the strocture of eye lens md ,1,t:1: the ,ole of 50 50
dllary mu1det ln tht hllffl.■ n tyt. / • 50an..
l!J [CJl~l O.,lhi S U 11. 2019] p I 100
Pow.,-of1helen,, • /(inmJ - f~nan)
ADI. Stm<tum Fib<ou>, jdly W., lltmdutt 1
Rolt-: To ch•ll8' the curvature o( ~ le.ns / to IIJO
P--- • 2D
changr the local lei,ath ol ey,e 1.,,., 50
[nlSF Mllkl•I ,;,b, .,,, 11H9j I Hent"I!, l)'W! l.'OfT«IIVe Jen• l11 \.01\VII'~ b«.auar pow"r
Q. 3. The power of I lf'n• l1 ♦5 dlopl•r, Wh.at 11 the
o(1entll potltl~. J
rututt and f«1J ltngth al lhl• ltnt1 At what Q. 2, (•I A J"'ttOn It ••fl•ring from bo<h mynpl• and
dllt.antt from 1h11 ll-n• thould .an abJ,ct b~ p~t•d hyp<nutropla
to " to get ita lnvr.rt~ ~ ot tht tame the 1 (I) Wb.a kind of 1,,_, on <Olff<I lhlt dtft<t l
(bID fO•l<lde Pclhl SIT II, 11119) CU) How ue lh•1t I.,.... pt<p>.ttd 1
Q. ~. WMI I• mu111 by pow.-r of • Im, l \"11,i doft (b) A person nerds a lmsofpowa + 30 forconl'cting
its sign (+ve or-ve> ind.iute 7 Sbte its S.J. uniL hif nt.u vilion a.nd -30 for corttd:ing hi., di1Wlt
How It th.ls unit ttblt!rrd to roe:.11I 1eng1J, of a vitlon. CilC'Ubte tht f0<al length, or the le:nset
leM 1 ,0l!J [CBSE Dl'lbl S.t LU, 211 161 rrqulr•d to corrttl thew de/ects.
Q. !. {.i) Write lhe function of e..ch of the fallowing p1ull
fll lCBSE O• l!id t 0.lhi S.t - L 20?111
/Int, (a) (I) The type of l,111 r,qulttd by 1uch J><l1011 10
of hM\lft •~-1 lmpMVf the v1,•on 11 bUocnl 1,m.
Cl) Come• Ill) Id ■
,111, Cry1ualllnt lf'?!J!Y) cm,ry muM'IH (II) A blf'ocAI lent eotlAltll of both c·o,wt,c le1u and
conc4w lenttt. Tht conv~ lt1u ulltd in bifocal lei,,
~ ID IC6~ U.lhi,O,l)., 2011) l, U6td 10 Mrrtrn hyptnl~lroplA (fll.r8lghttd1\HI)
Au, (1) ~ of, And <"one.we Len, is used 10 correel n,yopla (1hort•
Pl Cornu, ,..,.,... ligl,1 ray,,/ pmnl,. the Ughl sightcdn~,).
to fflter 8\t t)'t". I
(b) P• /
(ill Ids: C,,.,tmls amount of.tight entering 11,e "Y"
and the olz.e of pupil. I
(Ii) Cryotallin, Lau: Conv'"'S"' ligl!I ray,, at P, = +3D= /,
retina.
(Iv) Cill•ty Mot.Ide,, Adjuota focal 1,ngth of ">"' I
F,=- 3m = + 0.33 m (Convc,c 1,1'11)
i.m by contnellon and relmtton oo that
1lwp ln11ge can be obtained on the reun1. / I
http• In ac:a,cnn'IOdAUon r, • -3D • f,
ILIISt MA1JJng !,ct,..,,., 211181ll><, •1 I
f 1• - - • -0.Jl m. (Concav~ ~ru)
3
<@> Short Answer Type 11+1•31
Ouestlon11-II (3 marb each) Q. l, A &badfflt nttd• ~ of power-0.5 D for Utt
Q. J. The nur point of tht eyt of .a p,trton ii 50 on. C'Orrtction of hi1 vision.
Find lhe O.IIUlff' .and pow•r of lht' n,rrfftlve l•n.t (l) N""' the dtltct In vltl°" tht ltvdtnl is ""1ttring
mi,dr«t by the p<flOII to .,,.i,a, him too« dudy from.
the obj«t. pl,at'ed al 25 cm. Crom Uw -,,.. (ill Find !ht nahltt and low la,gth of lht
1J 11.'. IISL IJ<lld b<I - 111, W.OJ rnrrttt.lYI! l~u.
I HUMAN F.YE AND COLOURFUi. WO RUl Im
(W) Lbt two<•"'" ol lhh dd«t A noru\ill ')"C 1t not able tu tee dbtinctJy dw ubjt'Cb
t1 IC8SE O•t,ld• 11,>lhl, !><~ Ill, 201f) placed cloter wn :i., en, without puttlnll any 11raln
on lhe ,y,,. This 14 be(.tUM.' lhf' d lll\,Y m1.1M'.1' ,... ol t)'H
An,, II) Myopl,I
(U) Co.,aiv, I dlvCIJ!lng Ion• 11,d l<>cal
I
)\
... w\ll~c IO <Olltrul bey,,t\d a """"b' llndL u dw
obi«U are pl•c«I •I • dl!l•nce 1"' lh.,, lS cm ,,.,,,,
Lm8')1 • :lOil cm IS IN' "Y'• tMn 1h, ohJt'l"lt 'I'S""'' bh11ffd ~uM! 1ight
(Ill) (a) l!l<cflllw c:wv•ture o( th, oyr ltn• )\ r.tyt coming from the o~-d meet bc)-olld llw NU11i1,
(b) Elongado11 of eye boll 1+1+1
1c.11st MJ,king :.cn,mc, ~19J ll Q. ,. Du, to gr•dll41 WHk•nlna ,,, dlluy mu9C'IH Ind
Dcit.11.ikld Aru1Wr1 dlminl1hl:r'l8 OHibJUty ot lhc: ~ leN a cc-rt.In
(I) N t £ilti'•lt poW'ff thOWI IM t ltn!I 1, MelCAYt, ffl lht defed of Wfon ad1u, Write thlf' n...meof thiJ defttL
11uatnt 11 &ufltfii1g Crom n1yoptl/nt-lnlgh1ed nffl. Nuu tht typt of Jtn.t ttqulttd by • uth pf'rlOnt
(ii) Titc nature of le1a UK!d lo corttct this defect b to lmproYe the viaion. Explain thr 1truduff and
concave lens. lvndlon ol tv<b lent. QI!) fOdhl ll/1/1 20111
Focal length. /• -pI Ano. Prebyopia
Btr«at le n1
I
• (-0.5) • - 2m Upper portiocv'parl - Com:.aw Dna,rgjng lAtns
liill C,u,n ol ddect art: To view far o(£objecls
(a) Excr.ssive curvature of the ey e lens. Lower part ConY'e</oonvctgh,g lenl
(b) Elongalio.n of tl,c ey.i..n. To ladHlli,/ view nearl!y
Q.t. What it mun.I by powu ot a Ltn1 7 Writt tht St objcdf
uniL A sh,,dent ma ,a tens of fool .Lmgth 410 cm IOSE M•ll<lng Scb<m<, IIOl'71 l
.ind mother a.f - 20 cm. Write the n.ahue .ind power
ohuh ,.,... ~ Q fCCUSE D• lhl !l,t I, 2018) 0.il•tlfd At1t'°''~t1
Q. 5, With tht htlp of dUary muJC.ltt, tht hvm.an tye 1hr d efflcl u,uwd d u, 1.0 gradual we.a.bning t1I
can chmge Jt:J c,uvatutt and t.hut altf'r the foc.S dllAry mu,c:l<s and dlmlnltl~l'll O<>dbWty of th, •ye
le:nsth of lb lcu. State lht ch&n,c,.. th.It ocau ln 1~,u l.1 prHbyoplA,
ttw curv,ture and foc,al t«ngth of the ~ t lc.nt while Th11 IYJ)lo '1! l~n• n.•quhwl by tud , p111n on lo Improw
vl,wlng: (I)• dl, 1,nl abjHI, (II) n"rby oh)ttjj. th.: vii:lon b bilUCit.l lcnt,
l!,ipl,11,\ why a lUlffll&l cy• b nol &bl• w,.. dbdnclly
11w ob)«I pl,c<,d doter INn :i,_..,..,, wllhoul pulling A bl(OCAI lent cons.tstt ol both COt\Yt x lent and
1ny atnu\ on th~ t.'fit. m roc-thl 11/1/2 10J1J cona w ltnlff, Th, t o,w,x l,n.1 uu-d In bUocal ltna
An._ (I') Whtl\ w,, tiff dlltat\l ohj«.l-. lht cillary muklet ls ur.ed 10 cc,rrm hypernw,tropl• (IAt1lghlr.d1loN1)
~taxkxpa1d to dc.'(ffatc the curv.iture ai1d tJicn:by and concavt ltnt ts uJNt N> correct myopl.a (short•
iUm!tit! the focal length uf lhc l1.!tlll. HcOCl!, th!! lerlll 1lghtfdnHo),
bl•com es lhin. i1ti1 enables ~ lo Si..'t' thr disuJtl objt."Cl Q. 1, Write .a.haul paWt!t of •«om.mod.ation of hum•n
dearly. Thus., 1l1e for.Al ~nglh ol th~ eye l~ns IOO"l':.ues qe. Explain why the image dbunte In I.be q,r
whllP lf!f'lng di11a n1 object,,, dMJ not ch.tngt when wt changt tbt dJtl~ of
,n obj•<I from th• eye l (?,ID (Oclhl 11/lil 2011I
Q. 8 A pert0n It un~blt to 8ft dltllnd ly tht wordt
printed on• nr:wtp,apeL Namtt tht defrd of ,'W.00
ht luwferinglrom. Dr,w ray clugrltt\ IOillu!lttalf
thUI de(N"t. U sl ils two poti1bl e (:.IUSH, Or.aw• ,..ay
di.lgram to show how this de-led may be> conedrd
u1lng • I"" o( "JlpOOprl,llt focal ltnglh.
l!I fO• D•l Compu. Sl/1/S 1n17)
Ill) To lff th• n.-•roy obtect, d•arly, th• l«•I longth Sol• • Hypcm\Otrop~ Fanlgt,lfdncu I
of the Jens •hould be:: shorter. Fur lhl,, U11: c:iliruy • o.lmlvccy.
muM:'IPJ rnntract tn lncr,aw the n1tv.llun> and
thereby d<O'C.'U< lh< !oalJ l,ngth of the l<n~ Hn\tt,
llv lent becfKUH thick. Thi, en.a.bin you to 1ee lh e
nffrl>y obJ«tt clcorly.
0 -
--
lnt1\),;l'
Oblt'<'I Two ai11Mt:
(Q The focal '""gth ol the eye l<n• lo too loo1g. l
(II) Tlw eyel>AR hu bf<offl• IOo ,man.
m Osw•nl ces•~ Qui:alion B• nk Chaplenriae (k Toplcwi•e. ICIENCB, c1.... x I
• Confflion of lhir defect using approprlale lens Q. l, (a) A thldl.!:nt .la unablt to ,er dudy the wordJ
wriUPJ\ on lhe bl.1tk boud pl.1rl!d .at .a dl1lanC'e ot
appN>idmlldy 3 m from hhn. Nam, 1M dtl«t ol
vision the boy Ja suite.ring trom. Sto1h~ th, possibh,o
lnu1st• (At.Ifft or thlt d<t.fttl .tnd txpldn the mtlhod or
«>rtt<ting IL t!J
0 (b) Why do ,tan twlnlt.l• 7 bplal:n,
Conv~~x Ll!li )l"O',~ D•l hl/0,0 ., 11118)
lt•1ll'
Am. (11 DefKI ol vl1lon -Myupla or lhort4181>i.ch-
IC:PSti M••kl113 S<h,mc, tll111 ., ntartlghl<dnt1t
Q. 6. fa) Or•w • r.y dl•anm lo 1how the (orm•tlon o( ~ - o1 m70pla1 (II S.Cfl&ivc curvAIUtt ol cyo
lm.qe by • convex l1:n1 when an objtcl I• pla«-d len• ~cnn more conwrg,ing
ln front o( the ltN bctwttn Jt1 opUcal centrt and
(II) Elansallon ol f)l• l>AII
principal lonu.
tb) In lhfi ilbove ray dl.tgrim muk lht objert-d.111.ance Molhodt ol <Om<Horu By IJ,t UI< of C'Ollctvt
(w) And th11 lmt9•dl1~ntt. (ll) with llwlr prop•r l,011 or ,uli.b., .-..- or focal l•ngth tho dtlori
1lgn1 (+ ve or - ve H per the new Cartni•n algn 11 c;om:cted. It CIIII be nrpn."lenlcd by a 1ui11ble
convmtion) and 1tatt how that d.itlancH are dlls,amm1tl< rtPffl"nl1ttoo.
ttl11fd to tht foc.a,l lugth (/) o( lhf' tOl'IVtx lenl ln (b) Ou• to Atn,o,phtrlr rtlr1<tlon
thl1cu,• . The dtnalty o/ dlff.,..., l1y,r1 ol 11, 1cttp on
(c) find the power of ~ a,nvn lms whkh fo.rrru ~
clwlging due to whidt thr •pp,t~nt lmagcs al. the
t t ~ md invfflrd lnugi! ol tn.ap.iflcation -1 of an
objtt:I plJttd .al "ditb.nce o( 20 cm from Ill 0.1._lk.tl ,i.n lcHj> on cl>Anglng. Thi• changing JJOMll•n• of
cenbe. UJt.'\! ,tart appeor u twlnltling of stars.
-'•._ l•I [CBSE ~u.ti:ng ll<h•m•, 2018] 5
Ut!tdkd J.\JltWff:
A'
(a) Tht dtftct ls Myopli or &hort..gtghttd.nfN l.t.,
Inability of an ey, in viewiJ,g long dbuncc objects.
This defect is eoused by elongation o( eyf!ball and
exttS8iW curvatutt of the ~ru-
n· P, The short-sightedness is cmm:ted. by using a
cone.aw lens which diverges and shilts the iluage to
the ttdn.a,

I
(l.uaJJd u ys coming fn1m
{b) Relation: lfi'°l.-ml oh!,'i:t

(c~m • -1;" • -20cm;o • 1,/• 1

Marking of 1, & v

-
"' -••
o • + 20cu,
Thu, obl«t Is at :z.F
,.1,, 2f • 20an
I • 10 (fl\ • O.lm
p• 2
I
• _!_ • • 100
0,1

<@) Long Answer Type

Oue1tlon■ (5 11u:,r1t1 each)
Q. 1. W)un do we coruld.e:r ~ penon &o be myopk o.r hy•
permetropk 7 u,a lwo CiUletl of hyprrmetropiL. (b) Stanarevctydisbmt 1md11ppr0Xinut.ttly point-med
Expl.tln Dling R)' d1.agnms how the ddect aaod- foOUl'l"'H. Path ol sta.r light ch,mge,s m nllnuoualy duit
atrd with hypmnm-oplc eyt c,n bt corrttttd. to gradual cl\llns, b> relrlldiv• IJ\dex ol the l.\y.,.
O}t!J [C BS E 0..bide Oel h~ S.1-1, 2019] o( earth's at:mo5phu~. Thus, lhr 4ppi1Rnl positiom
-----=
'2) Th,wt -.iiun, ,..,jfll' ,,,__ff11,trl 1hW _..,_, _._w,,_, dv tfM ll{tb,,tMfl"'
I uf the stan fludua~ and thr a.u.tou.nt of ttar light
HUMAN EYE AND COI..OURF\11. WORIJl -

of lb.11 dd«L Explain l:ht mdhod 0£ corrtcting

enlering 1he eye nJc:ffl giving the twinkling e(f«I. this dd'ect wilh the hdp ol • r•.y d.Lagrun.
l+l l!J iSQI\ 10181

£ Commonly Made Error

AM.(•) Powerol ,cl"Om.mod.ltlanJ n I• llw abltuyof 1M
~ le1u lo adju11 ll1 (0Nl lfn&lh.
Cllllry mu!(i., o( •l" .,. r'elpontlble (ord,1ng. In
► C.ndidahn goruinJly 8'1t con(UH'd whUct lb '""•I lmgth.
drawing the- rAY rtligr,.n\ In the- defects whethff (b)Myopll
the lmagc hu to be drawn bcfl)ft' or &lier rctlna, cau1n, fl) ExC'ftllw curvatu.N ol iht ff'fl lit:n1
(II) FJongatlon al .yob.In
Thia dmct ..... he - - " " by UMJ'3 • ...,..,...
-:~ :- Answering Tip len, ol 1ult1bl• power.
For 11y dlagnm rt(tr NCERT P•~ 189 flgure 11.2
► Cam!ldate1 thou.Id remember dl4t concave (1), (b) ind (c) (Cll'il' ~lltlJngSth••••• 11a111 ISi
len, ls utcd fut corrcdlng Myopll 11nd abo rl.,f.altf.d A 1HWtf 1
drAW 111'-'tf bf>fol'f> rttln1 whtn Myopl• lJ lhf! (•) Thi: abilityordwvrope!tyol tJu: c:ye lcm toodjusl ltJ
-C)'C dtlffl._ (O("Al Jfngth In ord,r to (oc,1J l'lnlh lltlll( and d lJIAnl
obja"ll iJ known H the! power o( 11ero11un0di1llon.
Q. l. t•• What ii me~t by the tum ' power 01 The component of eye that lJ rclpon.il.ble fur th~
attommod.ttlon' 1 Name the com]>(IN'.nt of eyt th.at powtr of acrommodaHMI IJ clllAry mu&de:t b«Au~
i.t tHponti.blt fur lht powu o( 11ccommod1tion. they Att rttpot\tiblt for d'IAl\ge ln ltt focc\l t.t:ngth.
(b) A th.ident &lttlng ,U tht bAC'k btnch In a d au hH (b) TIU' defect af vision is Myopi..:
dlfflcvlly In ,udlfl&. What cowd l>t hl• dtftd o(
vl•lon 1 Duw ray dl.1g,.im110 mwurate the lm.1gt. Cauao uf Myopia:
formation of tht blMk.bo.a.td wh#n ht 11Jl .1l lhe (0 (1) Ex<ff51Vt curvatul'f' of th~ eyt Jens.
back se.tt Cii) front se.iL SI.ale two poss.ibl.e c..tuses (il) ELongo\llon of eyeball
To correct myopia the concave lens placed in front al lh.e eye forms a virtual image o( dis1a.nt abject al far polnL
Fatal.kl ray, {l\.'m
diM1nt obJC\."I
i,11 lnflnil)')

I Hhl~i.' If.
fomwJ in
bon1 ol
• ln ,1 myopic eytt, l.m.tge o( disLtnt object is formed in franl of the rt'ti.na (and not on~ retina),

,,,..-...__ •Retina

F I
l¼lr point (If lm,1t;l' b
lhl' \!Yl' rnrmr d fin
l h1:: n;,'1101\

• Tht far poJnt of a myopic eye tJ ltN 11lan lnftulty.

l<ny11 .It'\' fin.I

diw:r,;rd by
rM.\1lt!I U)'~ f,om l' O llj'/l 'II ' " 'l\!l

,11,.l!ml 11bjt•II
L /
..---..c'Kctln.
-· 11
(111Infinit y>

1111,1~,• h, furn ll',I

Vlt1u i1l lmai;t1< lo frorll L\I
formed lit F II I(' n:"tin11
Conl!i'lve k!n11 In
1·orn•1.'1 m,vu,,1.i
m Oll'W•n.l C8Stt. Quu1lon Barile Ch11pl~•e & f opk.'Wl•e. I CISNClt, c,... X

Q.t. t•) /\ 1l\1dent •u.ffeMg from myopl• la nul.blc tu 1ft dl1Unctly the obJ«b pll~d beyo.nd Sm. L11t two poulble
I
tHIONI dwe lo whlcb lhlt ddttt of vlllon auy have &rlwn. With lhe help of ny dl.1gnm1, apl.tln;
(I) Why lht ,io4tnl It un,blt to Mt 41ttlnttly tht ohjt<tt platt4 btyon4 Sm from hi• f)'ff,
(IJ) Tht lypt of tht: tontttlvt lent utfd to rtttott ptOPf'r viii on ind how thlt dtfttt I• corttdtd by thf!' u.H
of thia ltn1.
(b) JI, in thiJ c.ue, the numaicll value of th.e foal kngth of the col'ffd:in le-.ns is 5 m. find lhe power of Utt
lens u pu the nev.' C..utesbn Qgn convention. [.IJIJ [OD li/1 20111

i Topper Answer, 2017

-
r,I
•·
~r•
.
.-
...
~
~

,.,....,.L i
. /

--- \
.,. , -:;..,
. .... . .....
~

I/
f) /
- .
. . - . - ..
l)rt, llr ll /\111rWf'r. I
C• ) ti) Titc ~tudcnl ll wui.bJe tu icie distinctly Ou~ 7 - ; -;
objttts plactd beyond 5 m from hlJ •tw M h•
I 1
U suficrit,g from myopia i.t., lll'arsighredn.4.'59 =---
where is a PftS01\ C.U\ see nearby ob~ dtarly -5 - -
but cannot see distant objects distinctly.
(ii) Conca~ lens can be U5ed as lhe rotted.Ive lens lo = -1 -0
restore proper vision. A ooc\Cave lens of suitable -5
power wilt bring the bnagt" back on to the retina /•-5m
1111d thw Iii, dcl«t Is comdtd.
'J'httt.11 • ! . l ._0,20 5
11 • -OO,P • -510 I -5