### Ray Optics Questions and Answers:

**Ques.** A neon sign does not produce

(a) Line spectrum

(b) An emission spectrum

(c) An absorption spectrum

(d) Photons

**Ques.** A symmetric double convex lens is cut in two equal parts by a plane perpendicular to the principal axis. If the power of the original lens was 4 *D*, the power of a cut lens will be

(a) 2 D

(b) 3 D

(c) 4 D

(d) 5 D

**Ques.** If refractive index of red, violet and yellow lights are 1.42, 1.62 and 1.50 respectively for a medium. Its dispersive power will be

(a) 0.4

(b) 0.3

(c) 0.2

(d) 0.1

**Ques.** Chromatic aberration of lens can be corrected by

(a) Reducing its aperature

(b) Proper polishing of its two surfaces

(c) Suitably combining it with another lens

(d) Providing different suitable curvature to its two surfaces

**Ques.** When a plane mirror is placed horizontally on a level ground at a distance of 60 m from the foot of a tower, the top of the tower and its image in the mirror subtend an angle of 90^{o} at the eye. The height of the tower will be

(a) 30 m

(b) 60 m

(c) 90 m

(d) 120 m

**Ques.** Colour of the sky is blue due to

(a) Scattering of light

(b) Total internal reflection

(c) Total emission

(d) None of these

**Ques.** The critical angle for diamond (refractive index = 2) is

(a) About 20°

(b) 60°

(c) 45°

(d) 30°

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**Ques.** Under minimum deviation condition in a prism, if a ray is incident at an angle 30^{o}, the angle between the emergent ray and the second refracting surface of the prism is

(a) 0°

(b) 30°

(c) 45°

(d) 60°

**Ques.** A converging lens is used to form an image on a screen. When upper half of the lens is covered by an opaque screen

(a) Half the image will disappear

(b) Complete image will be formed of same intensity

(c) Half image will be formed of same intensity

(d) Complete image will be formed of decreased intensity

**Ques.** A convex lens, a glass slab, a glass prism and a solid sphere all are made of the same glass, the dispersive power will be

(a) In the glass slab and prism

(b) Only in prism

(c) In the lens and solid sphere

(d) In all the four

**Ques.** The radius of curvature of convex surface of a thin plano-convex lens is 15 *cm* and refractive index of its material is 1.6. The power of the lens will be

(a) +1 D

(b) –2D

(c) +3 D

(d) +4 D

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**Ques.** A thin equiconvex lens is made of glass of refractive index 1.5 and its focal length is 0.2 *m*, if it acts as a concave lens of 0.5 *m* focal length when dipped in a liquid, the refractive index of the liquid is

(a) 17/8

(b) 15/8

(c) 13/8

(d) 9/8

**Ques.** The dispersive powers of glasses of lenses used in an achromatic pair are in the ratio 5 : 3. If the focal length of the concave lens is 15 *cm*, then the nature and focal length of the other lens would be

(a) Convex, 9 cm

(b) Concave, 9 cm

(c) Convex, 25 cm

(d) Concave, 25 cm

**Ques.** A motor car is fitted with a convex driving mirror of focal length 20 cm. A second motor car 2.1 m board and 1.05 m high is 4 m behind the first car. What is the size of the image of second car as seen in the mirror of the first?

(a) Breadth = 8 cm, height = 4 cm

(b) Breadth = 10 cm, height = 5 cm

(c) Breadth = 12 cm, height = 6 cm

(d) Breadth = 14 cm, height = 7 cm

**Ques.** An object has image thrice of its original size when kept at 8 *cm* and 16 *cm* from a convex lens. Focal length of the lens is

(a) 8 cm

(b) 16 cm

(c) Between 8 cm and 16 cm

(d) Less than 8 cm

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**Ques.** An imaginary line joining the optical centre of the eye lens and the yellow point is called as

(a) Principal axis

(b) Vision axis

(c) Neutral axis

(d) Optical axis

**Ques.** A convex lens is dipped in a liquid whose refractive index is equal to the refractive index of the lens. Then its focal length will

(a) Become infinite

(b) Become small, but non–zero

(c) Remain unchanged

(d) Become zero

**Ques.** An object is placed at a distance 20 cm from the pole of a convex mirror of focal length 20 cm. The image is produced at :

(a) 13.3 cm

(b) 20 cm

(c) 25 cm

(d) 10 cm

**Ques.** In order to obtain a real image of magnification 2 using a converging lens of focal length 20 *cm*, where should an object be placed

(a) 50 cm

(b) 30 cm

(c) – 50 cm

(d) – 30 cm

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**Ques.** Which mirror has a very wide field of _

(a) Concave

(b) Convex

(c) Plane

(d) None of these

**Ques.** Which source is associated with a line emission spectrum?

(a) Electric fire

(b) Neon street sign

(c) Red traffic light

(d) Sun

**Ques.** What is the ray that comes back from the surface after reaction called?

(a) Incident ray

(b) Refracted ray

(c) Reflected ray

(d) Diffused ray

**Ques.** The number of wavelengths in the visible spectrum

(a) 4000

(b) 6000

(c) 2000

(d) Infinite

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**Ques.** A lamp is hanging at a height of 4*m* above a table. The lamp is lowered by 1*m*. The percentage increase in illuminace will be

(a) 40 %

(b) 64%

(c) 78%

(d) 92%

**Ques.** The fine powder of a coloured glass is seen as

(a) Coloured

(b) White

(c) That of the glass colour

(d) Black

**Ques.** For a normal eye, the least distance of distinct vision is

(a) 0.25 m

(b) 0.50 m

(c) 25 m

(d) Infinite

**Ques.** An eye specialist prescribes spectacles having a combination of convex lens of focal length 40 *cm* in contact with a concave lens of focal length 25 *cm*. The power of this lens combination in diopters is

(a) + 1.5

(b) – 1.5

(c) + 6.67

(d) – 6.67

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**Ques.** The plano-convex lens of focal length 20 cm and 30 cm are placed together to form a double convex lens. The final focal length will be :

(a) 12 cm

(b) 60 cm

(c) 20 cm

(d) 30 cm

**Ques.** Retina of eye acts like …….. of camera

(a) Shutter

(b) Film

(c) Lens

(d) None of these

**Ques.** Line spectrum was first of all theoretically explained by

(a) Swan

(b) Fraunhofer

(c) Kirchoff

(d) Bohr

**Ques.** Ability of the eye to see objects at all distances is called

(a) Binocular vision

(b) Myopia

(c) Hypermetropia

(d) Accommodation

**Ques.** Line spectrum contains information about

(a) The atoms of the prism

(b) The atoms of the source

(c) The molecules of the source

(d) The atoms as well as molecules of the source

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**Ques.** The magnifying power of a simple microscope can be increased, if we use eye-piece of

(a) Higher focal length

(b) Smaller focal length

(c) Higher diameter

(d) Smaller diameter

**Ques.** In a compound microscope cross-wires are fixed at the point

(a) Where the image is formed by the objective

(b) Where the image is formed by the eye-piece

(c) Where the focal point of the objective lies

(d) Where the focal point of the eye-piece lies

**Ques.** A compound microscope has two lenses. The magnifying power of one is 5 and the combined magnifying power is 100. The magnifying power of the other lens is

(a) 10

(b) 20

(c) 50

(d) 25

**Ques.** Relative difference of focal lengths of objective and eye lens in the microscope and telescope is given as

(a) It is equal in both

(b) It is more in microscope

(c) It is more in telescope

(d) It may be more in any one

**Ques.** On which of the following does the magnifying power of a telescope depends

(a) The focal length of the objective only

(b) The diameter of aperture of the objective only

(c) The diameter of aperture of the objective and that of the eye piece

(d) The focal length of the objective and that of the eye piece

**Ques.** The length of a telescope is 36 *cm*. The focal lengths of its lenses can be

(a) 30 cm, 6 cm

(b) – 30 cm, – 6 cm

(c) 30 cm, – 6 cm

(d) – 30 cm, 6 cm

**Ques.** A lamp is hanging at a height 40 *cm* from the centre of a table. If its height is increased by 10 *cm* the illuminance on the table will decrease by

(a) 10 %

(b) 20%

(c) 27%

(d) 36%

**Ques.** Five *lumen/watt* is the luminous efficiency of a lamp and its luminous intensity is 35 *candela*. The power of the lamp is

(a) 80 W

(b) 176 W

(c) 88 W

(d) 36 W