6. C a p t e r at G l a n c e Ligt related penomena can be studied wit mirrors and lenses. A mirror is a reflecting surface wile a lens is a transparent material. Mirrors are mainly of tree types : plane mirror, concave or converging mirror, convex or diverging mirror. Lenses are mainly of two types : concave or diverging lens; convex or converging lens. Focal lengt of convex mirror is positive wile tat of concave mirror is negative. Focal lengt of convex lens is positive wile tat of concave lens is negative. Focal lengt ( f) of concave mirror is always negative, object distance (u) is always negative and image distance ( v) is negative in case of real and inverted image because tis type of image is formed on te same side of te mirror as tat of te object. Image distance ( v) is positive incase of virtual and erect image because tis type of image is formed beind te mirror. Mirror formula : + v u = f 2 M (magnification produced by sperical mirror) = = v u 2 = eigt of te image = eigt of te object 2 is negative for inverted image and positive for erect image. is always positive. Heigt upward (+ve) R Unique Solutions Focal lengt ( f ) of convex lens is always positive, object distance (u) is always negative and image distance ( v) is negative incase of virtual and erect image because tis type of image is formed on te same side of te lens as te object. Image distance ( v) is positive incase of real and inverted images because tese images are formed on te oter side of te lens as te object. Lens formula = v u = f Direction of incident ligt Heigt downwards ( ve) Figure : Representation of sign conventions. distance towards te left ( ve) Mirror distance towards te rigt (+ve) P principal axis
94 Unique MCQ's M (magnification produced by lens) = P (Power of lens) = f(in metre) Unit of power of lens is dioptre 2 = v u dioptre = l(metre) Cornea, pupil, iris, lens, retina and optic nerve are te main parts of uman eye. Cornea ligt enters te eye. pupil ligt is controlled and regulated. iris colour is different for different people. retina ligt sensitive screen. optic nerve pass electric signals to te brain. Defects of vision : Myopia or near sigtedness; Hypermetropia or long sigtedness; presbyopia or old age ypermetropia. Myopia image in front of retina corrected using concave lens. Hypermetropia image beind retina corrected using convex lens. Presbyopia suffer, bot myopia and ypermetropia corrected using bifocal lens. Concave or converging mirror is used in : torces and ead ligts; flood ligts; reflector or projector lamps; solar devices and furnaces; saving mirrors and dentists mirror. Convex or converging lens is used in : simple microscope, compound microscope; telescope, optical instruments like camera, projector, spectrometer, spectacles etc. MULTIPLE CHOICE QUESTIONS (MCQ's) MCQ's BASED ON PRACTICALS (Eac question carries one mark) Experiment : I. To determine te focal lengt of - a) Concave mirror b) Convex lens by obtaining image of a distinct object.. An object of 0 cm eigt is placed in front of a plane mirror. Te eigt of te image will be : a 5 cm b 0 cm c 5 cm d 20 cm 2. Te focal lengt of concave mirror in te given experimental set up is : a 0.3 cm b.0 cm c.7 cm d 2.2 cm
SCIENCE & TECHNOLOGY - S.S.C. 95 3. A students obtained a sarp image of grill of a window on a screen using a convex lens. For better results te teacer suggested focusing on a distant tree instead of grill. In wic direction sould te lens be moved to get te sarp image of tree? a away from screen b beind te screen c towards te screen d far away from screen 4. Inside water, an air bubble beaves : a always like a concave lens c always like a flat plate b always like a convex lens d sometimes like a convex lens and sometimes like a concave lens 5. Mirror used by a dental surgeon is : a plane b convex c concave d bot (b) & (c) 6. In a concave mirror ligt is reflected from : a inner surface c sperical surface b outer surface d inner and outer surface 7. Wat appens to te image of your face as you take a concave mirror away from your face slowly? a becomes smaller b becomes bigger c remains te same d disappears 8. Wen te object is far away from a concave mirror, te image is formed : a between focus and centre of curvature b at focus c at centre of curvature d beyond centre of curvature 9. A concave mirror forms enlarged virtual image for te position of te object : a between infinity and centre of curvature b between focus and centre of curvature c at te principle focus d between pole and principal focus. 0. Wen te object is at principle focus of a concave mirror, te image formed is : a magnified b igly magnified c diminised d igly diminised. To get te image at te centre of curvature of a concave mirror, te object must be placed : a between infinity and centre of curvature c at principal focus b at infinity d at te centre of curvature 2. A ray of ligt parallel to principal axis after reflection from concave mirror passes troug : a centre of curvature b focus c pole d radius of curvature 3. If a lens is ticker in te middle tan at te edges, it is a : a bifocal lens b diverging lens c concave lens d convex lens 4. A point sized image is obtained by a convex lens wen te object is : a between F and 2F b at 2F c beyond 2F d at infinity
96 Unique MCQ's 5. Te focus of a concave mirror lies : a on te bot sides of te mirror b in front of te mirror c at te back of te mirror d on te rigt side of te mirror 6. Te focal lengt of a concave mirror is : a positive b negative c zero d always positive 7. Te focal lengt of a convex lens is : a positive b negative c always negative d neiter positive nor negative 8. Wic of te following are used in solar furnaces? a concave lenses b convex lenses c concave mirrors d convex mirrors MCQ's BASED ON CHAPTER. Distorted images are obtained in Moderate Level a plane mirror b sperical mirror c concave lens d convex lens 2. Wic of te following forms an arc of a circle? a concave lens b convex lens c sperical mirror d plane mirror. 3. To get a convex mirror, wic side of a sperical surface is to be polised? a inner b outer c inner and outer d sperical 4. Diverging mirror is : a concave b convex c plane d sperical 5. Te centre of a sperical mirror is its : a centre of curvature b optical centre c focus d pole 6. If te incident ray passes troug te centre of curvature of a sperical mirror, te reflected ray : a passes troug te focus b passes parallel to te principal axis c traces te same pat d passes troug optical centre undeviated 7. Distances parallel to principal axis are measured from te : a optical centre of te mirror. b pole of te mirror c focus of te mirror d centre of curvature of te mirror 8. A lens aving bot surfaces curved inwards is : a double concave b double convex c bifocal d converging lens 9. A ray of ligt passes undeviated as it passes troug : a pole of te lens b focus of te lens c optical centre of te lens d centre of curvature of te lens 0. To get an image of te same size as te object, te object must be placed : a at 2F of a lens b at 2F 2 of a lens c at F of a lens d beyond 2F of a lens
SCIENCE & TECHNOLOGY - S.S.C. 97. Te image obtained wen te object is placed between focus and optical centre of a convex lens is : a diminised, virtual and erect b diminised, real and inverted c magnified, virtual and erect d magnified, real and inverted 2. Te ability of a lens to converge or diverge ligt rays depends on its : a principal focus b focal lengt c principal axis d optical centre 3. Te amount of ligt entering te eye is regulated by : a cornea b iris c pupil d eye lens 4. Some people ave bluis eyes due to teir blue coloured : a cornea b iris c eyelens d pupil 5. Te focal lengt of a normal uman eye lens in its relaxed position is about : a 2.5 cm b 25 cm c 2.5 m d 25 m 6. Hypermetropia is corrected using : a concave lens b convex lens c bifocal lens d cylindrical lens Elementary level. Te image formed by a plane mirror cannot be projected on a screen because : a it is a real image c reflected rays do not actually meet eac oter d reflected rays converge at a point 2. Te image formed by a plane mirror is : b it is formed in front of te mirror a virtual b real c magnified d inverted 3. Wic of te following image is not obtained on a screen? a diminised b inverted c real d virtual 4. Wic beam of ligt is used to concentrate ligt at a point? a converging b diverging c parallel d pointed 5. Diverging beam of ligt is used in : a torces b solar devices c table lamps d ead ligts 6. Wic of te following beam of ligt is used by an optalmologist to examine is patient? a parallel b diverging c converging d pointed 7. Were does te focus of a convex mirror lie? a in front of b beind c on bot sides d on te left side 8. Wic of te following is always negative? a object distance b image distance c object size d image size 9. Heigt of te image is to be taken as positive for : a real images b virtual images c inverted images d magnified images 0. Wic of te following is a natural optical device? a lens b mirror c eye d camera
98 Unique MCQ's. A lens is a/an : a opaque material b transparent material c translucent material d reflecting material 2. Wic of te following statement is false? a eac lens as two centres of curvature b every lens as two principal foci c eac sperical mirror as two centres of curvature d every sperical mirror as more tan one radii of curvature 3. Using a convex lens, a well defined image of a distant object is obtained on a screen. Te focal lengt of tis lens is : a te distance between te screen and object b te distance between te lens and object c te distance between te screen and lens d alf of te distance between te lens and object 4. Ligt rays bend troug large angles wen te focal lengt of a convex lens is : a sort b large c medium d zero 5. dioptre is te power of a lens wose focal lengt is one : a millimetre b centimetre c decimetre d metre 6. Negative sign of magnification sows tat te image is : a inverted and virtual b inverted and real c erect and virtual d erect and real 7. Te image formed on te retina of uman eye is : a real and inverted b real and erect c virtual and inverted d virtual and erect 8. For normal uman eye, te distance of distinct vision is : a 25 m b 2.5 m c 2.5 cm d 25 cm 9. In myopia, te image of te object is formed : a on te retina b in front of te retina c beind te retina d on te lens 20. In torces and eadligts, te source of ligt is placed : a at te centre of curvature of a concave mirror b at te focus of a concave mirror c between pole and focus of a concave mirror d beyond te centre of curvature of a concave mirror 2. In reflecting mirrors for projector lamps, te object is placed : a at te focus of a concave mirror b beyond te centre of curvature of a concave mirror c between pole and focus of a concave mirror d at te centre of curvature of a concave mirror
SCIENCE & TECHNOLOGY - S.S.C. 99 Complex Level. Te angle of incidence of an incident ray passing troug te centre of curvature of a sperical mirror is : a 90 b 45 c 0 d 60 2. Radius of curvature of a sperical mirror is : a smaller tan its focal lengt c trice larger tan its focal lengt Hint : f = R 2, R = 2f b twice larger tan its focal lengt d larger by 2 cm tan its focal lengt 3. If te focal lengt of eac a mirror and a lens is + 5 cm ten, a te mirror is concave, but te lens is convex b bot are concave c bot are convex d te mirror is convex, but te lens is concave. 4. Wic of te following formulae gives eigt of te image formed by a convex lens? a 2 = v u Hint : M = 2 = v u b = v 2 v c 2 = 5. Te value 2 = 3.5 cm sows tat te image is : v v d = a enlarged b diminised c erect d inverted 6. Te power of a convex lens wit focal lengt 40 cm is : a + 2.5 D b + 0.025 D c 2.5 D d 0.025 D Hint : P = f(in metre) 7. Focal lengt of a corrective lens aving power + 2D is : a 0.05 m b 0.05 cm c 0.5 m d 0.5 cm Hint : P = f(in metre) 8. Te negative power of te spectacles indicates te defect of vision : a myopia b ypermetropia c presbyopia d astigmatism 9. Since, Raul's grand fater is suffering from presbyopia, e wears spectacles aving : a convex lens b concave lens c bifocal lens d plane lens 0. Te power of a concave lens of focal lengt 20 cm is : a + 5D b 5D c + 0.5D d 0.5D v 2 u Hint : P = f(in metre)
00 Unique MCQ's Mysterious Level. Te focal lengt of a sperical mirror wit radius of curvature 2.6 cm is : a 3.2 cm b.3 cm c 5.2 cm d 0.3 cm Hint : f = R 2 2. Te radius of curvature of a sperical mirror wit focal lengt 0.7 cm is : a.4 cm b 0.35 cm c 3.5 cm d 0.4 cm Hint : f = R 2, R = 2 f 3. If te distance of te object from te origin is 2 cm and te image distance is 60 cm, magnification produced by te convex lens is : a + 0.2 b 0.2 c + 5 d 5 Hint : U M = v u 4. Wen a 4 cm tall object is placed at 0 cm away from a converging lens, an image is formed at a distance of 30 cm on te oter side of te lens. Te eigt of te image formed is : a + 2 cm b 2 cm c + 5 cm d 5 cm v Hint : 2 = u 5. An object is placed at a distance of 5 cm from a convex lens of focal lengt 20 cm. Te position of te object is : a 60 cm b + 60 cm c 90 cm d + 90 cm Hint : v = + u f 6. Wen a converging lens form an image of 45 cm, te magnification produced is 3. Terefore, eigt of te object is : a + 5 cm b 5 cm c + 30 cm d 30 cm Hint : m = 2 = 2 m 7. If te magnification produced by an object of eigt 0 cm due to a sperical mirror is 0.5, eigt of te image formed is : a 5 cm b + 5 cm c + 2 cm d 2 cm Hint : M = 2 2 = M 8. An object of size 5 cm is placed at 5 cm in front of concave mirror of focal lengt 2 cm. To get a sarp and clear image, at wat distance from te mirror a screen sould be placed? a 60 cm b 30 cm c 20 cm d 50 cm Hint : + v u = f v = f u
SCIENCE & TECHNOLOGY - S.S.C. 0 MCQ's BASED ON PRACTICAL SKILLS Answers - b 2 - b 3 - c 4 - b 5 - c 6 - a 7 - b 8 - b 9 - d 0 - b - d 2 - b 3 - d 4 - d 5 - b 6 - b 7 - a 8 - c MCQ's BASED ON CHAPTER Moderate Level - b 2 - c 3 - b 4 - b 5 - d 6 - c 7 - b 8 - a 9 - c 0 - a - c 2 - b 3 - c 4 - b 5 - a 6 - b Elementary Level - c 2 - a 3 - d 4 - a 5 - c 6 - c 7 - b 8 - a 9 - b 0 - c - b 2 - c 3 - c 4 - a 5 - d 6 - b 7 - a 8 - d 9 - b 20 - b 2 - d Complex Level Mysterious Level - c 2 - b 3 - c 4 - a 5 - d 6 - a 7 - c 8 - a 9 - c 0 - b - b 2 - a 3 - d 4 - b 5 - a 6 - a 7 - a 8 - a