Capter 0 Ligt- Relectiion & Reraction Intext Questions On Page 68 Question : Deine te principal ocus o a concae irror. Principal ocus o te concae irror: A point on principal axis on wic parallel ligt rays conerges ater relecting ro te irror. Question 2: Te radius o curature o a sperical irror is 20 c. Wat is its ocal lengt? Radius o curature, R = 20 c Radius o curature o a sperical irror = 2 Focal lengt () R 2 0c Hence, te ocal lengt o te gien sperical irror is 0 c. Question 3: Nae te irror tat can gie an erect and enlarged iage o an object. Wen an object is placed between te pole and te principal ocus o a concae irror, irtual, erect, and enlarged iage is ored. Question 4: Wy do we preer a conex irror as a rear-iew irror in eicles?
Conex irrors ors a irtual, erect, and diinised iage o te objects tat are placed in ront o te. Tese irrors gie a wider ield o iew, wic allows te drier to see ost o te traic beind i. Tus, tey are preerred as a rear-iew irror in eicles. On Page 7 Question : Find te ocal lengt o a conex irror wose radius o curature is 32 c. Radius o curature, R = 32 c Radius o curature = 2 Focal lengt () R 2 R 2 6c Hence, te ocal lengt o te gien conex irror is 6 c. Question 2: A concae irror produces tree ties agniied (enlarged) real iage o object placed at 0 c in ront o it. Were is te iage located? Magniication produced by a sperical irror is: Heigt o te iage Heigt o te object 0 u Iage distance Object distance Let te eigt o te object, o = Ten, eigt o te iage = 3 3 u 3 u
Object distance, u = 0 c = 3 ( 0) = 30 c Here, an inerted iage is ored at a distance o 30 c. On Page 76 Question : A ray o ligt traelling in air enters obliquely into water. Does te ligt ray bend towards te noral or away ro te noral? Wy? We know tat, ligt ray bends towards te noral. Water is optically denser tan air; a ray o ligt traelling ro air into te water will bend towards te noral. Question 2: Ligt enters ro air to glass aing reractie index.50. Wat is te speed o ligt in te glass? Te speed o ligt in acuu is 3 0 8 s. Reractie index o a ediu, n speed o ligt in acuu speed o ligt in ediu c Speed o ligt in acuu, c = 3 0 8 s Reractie index o glass, n g =.50 n c 30.5 8 8 2 0 /s Tus, Speed o ligt in te glass = 8 20 /s Question 3: Find out, ro Table, te ediu aing igest optical density. Also ind te ediu wit lowest optical density.
Material ediu Reractie index Material ediu Reractie index Air.0003 Canada Balsa.53 Ice.3 - - Water.33 Rock salt.54 Alcool.36 - - Kerosene.44 Carbon disulpide.63 Fused quartz.46 Dense lint glass.65 Turpentine oil.47 Ruby.7 Benzene.50 Sappire.77 Crown glass.52 Diaond 2.42 Optical density o a ediu is directly related wit te reractie index o tat ediu. A ediu wic as te igest reractie index will ae te igest optical density and ice-ersa. Higest optical density = Diaond Lowest optical density = Air Question 4: You are gien kerosene, turpentine and water. In wic o tese does te ligt trael astest? Use te inoration gien in Table.k Speed o ligt in a ediu is gien by te relation or reractie index (n ). Te relation is gien as n speed o ligt in acuu speed o ligt in ediu c n n c Ligt will trael te slowest in te aterial wic as te igest reractie index and trael te astest in te aterial wic as te lowest reractie index. It can be obsered ro table 0.3 tat ligt traels te astest in water. Question 5: Te reractie index o diaond is 2.42. Wat is te eaning o tis stateent? Reractie index o a ediu n is related to te speed o ligt in tat ediu by te relation:
n speed o ligt in acuu speed o ligt in ediu c Te reractie index o diaond is 2.42. Tis eans tat te speed o ligt in diaond will reduce by a actor 2.42 copared to its speed in air. On Page 84 Question : Deine dioptre o power o a lens. Power o lens: It is deined as te reciprocal o its ocal lengt. I P is te power o a lens o ocal lengt F in etres, ten P Te S.I. unit o power o a lens is Dioptre. It is denoted by D. dioptre is deined as te power o a lens o ocal lengt etre. D = Question 3: Find te power o a concae lens o ocal lengt 2. Focal lengt o concae lens, = 2 P P P 2 0.5D Here, negatie sign arises due to te diergent nature o concae lens.
Hence, te power o te gien concae lens is 0.5 D. Question 3: Find te power o a concae lens o ocal lengt 2. Focal lengt o concae lens, = 2 P P P 2 0.5D Here, negatie sign arises due to te diergent nature o concae lens. Hence, te power o te gien concae lens is 0.5 D. Exercise Question : Wic one o te ollowing aterials cannot be used to ake a lens? (a) Water (b) Glass (c) Plastic (d) Clay (d) Clay Question 2: Te iage ored by a concae irror is obsered to be irtual, erect and larger tan te object. Were sould be te position o te object? (a) Between te principal ocus and te centre o curature (b) At te centre o curature (c) Beyond te centre o curature (d) Between te pole o te irror and its principal ocus.
(d) Between te pole o te irror and its principal ocus. Question 3: Were an object sould be placed in ront o a conex lens to get a real iage o te size o te object? (a) At te principal ocus o te lens (b) At twice te ocal lengt (c) At ininity (d) Between te optical centre o te lens and its principal ocus. (b) At twice te ocal lengt Question 4: A sperical irror and a tin sperical lens ae eac a ocal lengt o 5 c. Te irror and te lens are likely to be (a) Bot concae (b) Bot conex (c) Te irror is concae and te lens is conex (d) Te irror is conex, but te lens is concae (a) By conention, te ocal lengt o a concae irror and a concae lens are taken as negatie. Hence, bot te sperical irror and te tin sperical lens are concae in nature. Question 5: No atter ow ar you stand ro a irror, your iage appears erect. Te irror is likely to be (a) Plane (b) Concae (c) Conex (d) Eiter plane or conex (d) Eiter plane or conex
Question 6: Wic o te ollowing lenses would you preer to use wile reading sall letters ound in a dictionary? (a) A conex lens o ocal lengt 50 c (b) A concae lens o ocal lengt 50 c (c) A conex lens o ocal lengt 5 c (d) A concae lens o ocal lengt 5 c (c) A conex lens o ocal lengt 5 c sould be used. Question 7: We wis to obtain an erect iage o an object, using a concae irror o ocal lengt 5 c. Wat sould be te range o distance o te object ro te irror? Wat is te nature o te iage? Is te iage larger or saller tan te object? Draw a ray diagra to sow te iage oration in tis case. Range o object distance = 0 c to5 c A concae irror gies an erect iage wen an object is placed between its pole (P) and te principal ocus (F). Hence, to obtain an erect iage o an object ro a concae irror o ocal lengt 5 c, te object ust be placed anywere between te pole and te ocus. Te iage ored will be irtual, erect, and agniied in nature. Question 8: Nae te type o irror used in te ollowing situations. (a) Headligts o a car (b) Side/rear-iew irror o a eicle
(c) Solar urnace Support your answer wit reason. a) Concae irror is used in te eadligts o a car because concae irrors can produce powerul parallel bea o ligt wen te ligt source is placed at teir principal ocus. b) Conex irror is used in side/rear iew irror o a eicle. Conex irrors gie a irtual, erect, and diinised iage o te objects placed in ront o it. Because o tis, tey ae a wide ield o iew. It enables te drier to see ost o te traic beind i/er. c) Concae irrors are conergent irrors. Tat is wy tey are used to construct solar urnaces. Question 9: One-al o a conex lens is coered wit a black paper. Will tis lens produce a coplete iage o te object? Veriy your answer experientally. Explain your obserations. Te conex lens will or coplete iage o an object, een i it s one al is coered wit black paper. Case I: Wen te upper al o te lens is coered. In tis case, a ray o ligt coing ro te object will be reracted by te lower al o te lens. Tese rays eet at te oter side o te lens to or te iage o te gien object. Case II: Wen te lower al o te lens is coered In tis case, a ray o ligt coing ro te object is reracted by te upper al o te lens. Tese rays eet at te oter side o te lens to or te iage o te gien object.
Question 0: An object 5 c in lengt is eld 25 c away ro a conerging lens o ocal lengt 0 c. Draw te ray diagra and ind te position, size and te nature o te iage ored. Object distance, u = 25 c Object eigt, o = 5 c Focal lengt, = +0 c According to te lens orula, u u 0 25 5 250 6.66c Te positie alue o sows tat te iage is ored at te oter side o te lens. Iage distance 6.66 Magniication, 0.66 Object distance u 25 Te negatie sign sows tat te iage is real and ored beind te lens.
Magniication, Heigt o te iage ' eigt o te object 5 ' 0.665 ' 3.3c Te negatie alue o iage eigt indicates tat te iage ored is inerted. Question : A concae lens o ocal lengt 5 c ors an iage 0 c ro te lens. How ar is te object placed ro te lens? Draw te ray diagra. Focal lengt o concae lens (OF ), = 5 c Iage distance, = 0 c According to te lens orula, u u u 0 5 u 30 u 30c Te negatie alue o u indicates tat te object is placed 30 c in ront o te lens. Tis is sown in te ollowing ray diagra.
Question 2: An object is placed at a distance o 0 c ro a conex irror o ocal lengt 5 c. Find te position and nature o te iage. Focal lengt o conex irror, = +5 c Object distance, u = 0 c According to te irror orula, u u 5 0 6 6c Te positie alue o indicates tat te iage is ored beind te irror. Iage distance 6 Magniication, 0.6 Object distance u 0 Te positie alue o agniication indicates tat te iage ored is irtual and erect. Question 3: Te agniication produced by a plane irror is +. Wat does tis ean?
Magniication produced by a irror is gien by te relation Magniication, Iage eigt (H ) Object eigt (H ) 0 Te agniication produced by a plane irror is +. It sows tat te iage ored by te plane irror is o te sae size as tat o te object. Te positie sign sows tat te iage ored is irtual and erect. Question 4: An object 5.0 c in lengt is placed at a distance o 20 c in ront o a conex irror o radius o curature 30 c. Find te position o te iage, its nature and size. Object distance, u = 20 c Object eigt, = 5 c Radius o curature, R = 30 c Radius o curature = 2 Focal lengt R = 2 = 5 c According to te irror orula, u u 5 20 7 60 8.57c
Te positie alue o indicates tat te iage is ored beind te irror. Iage distance 8.57 Magniication, 0.428 Object distance 20 Magniication, Iage eigt Object eigt ' ' ' 0.4285 ' 2.4c Te positie alue o iage eigt indicates tat te iage ored is erect. Tereore, te iage ored is irtual, erect, and saller in size. Question 5: An object o size 7.0 c is placed at 27 c in ront o a concae irror o ocal lengt 8 c. At wat distance ro te irror sould a screen be placed, so tat a sarp ocused iage can be obtained? Find te size and te nature o te iage. u 27c 7c 8c u u 8 27 54 54c
Iage distance 54 Magniication, 2 Object distance 27 Te negatie alue o agniication indicates tat te iage ored is real. Magniication, Heigt o te iage eigt o te object ' ' 7 2 ' 4c Te negatie alue o iage eigt indicates tat te iage ored is inerted. Question 6: Find te ocal lengt o a lens o power 2.0 D. Wat type o lens is tis? Power o a lens, P P 2D 2 0.5 A concae lens as a negatie ocal lengt. Tus, it is a concae lens. Copyrigt Jagranjos.co All rigts resered. No part or te wole o tis ebook ay be copied, reproduced, stored in retrieal syste or transitted and/or cited anywere in any or or by any eans (electronic, ecanical, potocopying, recording or oterwise), witout te written perission o te copyrigt owner. I any isconduct coes in knowledge or brougt in notice, strict action will be taken.