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Question Bank No: 2

1. An object is placed 12 cm to the left of a converging lens of focal length 8 cm. Another converging lens of 6 cm focal length is placed at a distance of 30 cm to the right of first lens. The second lens will produce

a)		a real enlarge image
b)		a real inverted image
c)		no image
d)		a virtual enlarged image

2. A vessel of depth 2d cm is half filled with a liquid of refractive index $μ_{1}$ and the upper half with a liquid of refractive index $μ_{2}$ . The apparent depth of the vessel seen perpendicular is

a)		d $(\frac{μ_{1} μ_{2}}{μ_{1} + μ_{2}})$
b)		d $(\frac{1}{μ_{1}} + \frac{1}{μ_{2}})$
c)		2d $(\frac{1}{μ_{1}} + \frac{1}{μ_{2}})$
d)		2d $\frac{1}{μ_{1} μ_{2}}$

3. A plane mirror produces a magnification of

a)		$- I$
b)		$+ I$
c)		zero
d)		between 0 and + $\infty$

4. The magnifying power of an astronomical telescope is 8 and the distance between the two lenses is 54 cms. The focal length of the eye-lens and objective lens will be respectively

a)		6 cm and 48 cm
b)		48 cm and 6 cm
c)		8 cm and 64 cm
d)		64 cm and 8 cm

5. A lamp hanging 4 meters above the table is lowered 1 metre. How much percent is the increase in the illumination on the table?

a)		25%
b)		52%
c)		77.7%
d)		No increase

6. In the method of displacement to determine the focal length of a convex lens the distance between the object and the screen is D and real images of an object are formed on the screen for two positions of the lens which are seperated by a distance x. The ration of the sizes of the two images will be

a)		$\sqrt{D / x}$
b)		${(\frac{D - x}{D + x})}^{2}$
c)		$D^{2} / x^{2}$
d)		D/x

7. A convex lens of focal length 1.0 m and a concave lens of focal length 0.25 m are 0.75 m apart. A parallel beam of light is incident on the convex lens. The beam emerging after refraction from both lenses is

a)		parallel to principal axis
b)		convergent
c)		divergent
d)		none of these

8. A concave lens made of water ( $μ = 1.33)$ is placed inside a glass slab ( $μ = 1.5)$ for an object placed within the focus and twice the focus, the image formed is

a)		virtual
b)		real, inverted and magnified
c)		virtual, inverted and magnified
d)		real, inverted and diminished

9. While taking photographs with a camera if one wants that every object beyond one metre should be in focus, one should

a)		give short exposure without changing aperture
b)		reduce the aperture and increase the time of exposure
c)		increase the aperture and reduce the time of exposure
d)		give long exposure without changing the aperture

10. A convex lens of focal length f is placed somewhere in between an object and a screen. The distance between an object and the screen is x, if the magnification produced by the lens is m, the focal length is

a)		$\frac{{(m - 1)}^{2}}{m}$
b)		$\frac{{(m + 1)}^{2}}{m} x$
c)		$\frac{mx}{{(m - 1)}^{2}}$
d)		$\frac{mx}{{(m + 1)}^{2}}$

11. The focal length of a concave mirror island the distance from the object to the principal focus is p. Then the ratio of the size of the image to the size of the object is

a)		$\frac{f^{2}}{p^{2}}$
b)		$\sqrt{\frac{f}{p}}$
c)		$\frac{f}{p}$
d)		$\frac{f + p}{p}$

12. A telescope has an objective of focal length 50 cms and an eye- piece of focal length 5 cm. It is focussed for distinct vision on a scale 200 cms away from the objective. Then the optical length of the telescope is

a)		200/3 cms
b)		25/6 cms
c)		425/6 cms
d)		375/6 cms

13. A thin convex lens of focal length 30 cm and refractive index 1.5 is placed on a horizontal plane mirror. It is found that an object, at a height 'h' above the lens, has no parallax with its image. Then h is

a)		60 cm
b)		30 cm
c)		45 cm
d)		20 cm

14. In the displacement method of finding focal length of a convex lens $\sqrt{l_{1}}$ and $l_{2}$ are the sizes of the images respectively for two positions of the lens. The size of the object is

a)		$\sqrt{l_{1} / l_{2}}$
b)		$\sqrt{l_{2} / l_{1}}$
c)		$\sqrt{l_{1} l_{2}}$
d)		$l_{1} l_{2}$

15. A mark 'A' placed on the surface of a glass sphere is viewed through glass from a point directly opposite. Radius of sphere = 10 cm. Refractive index of glass is 1.5. Which one of the following statement is correct?

a)		The image formed is real and at a distance of 0.4 m from the eye
b)		The image formed is virtual and at a distance of 0.2 m from the eye
c)		The image formed is virtual and at a distance of 0.3 m from the centre of the sphere
d)		The image formed is real and at a distance of 0.2 m from point A

16. A lens is placed between a source of light and a wall. It forms images of area $A_{1}$ and $A_{2}$ on the wall, for its two different positions. The area of source is

a)		$\frac{A_{1} + A_{2}}{2}$
b)		${[\frac{1}{A_{1}} + \frac{1}{A_{2}}]}^{- 1}$
c)		$\sqrt{A_{1} A_{2}}$
d)		${[\frac{\sqrt{A_{1}} + \sqrt{A_{2}}}{2}]}^{2}$

17. The figure shown here is a converted lens placed inside a vessel filled with liquid. The lens has focal length +20cm when in air and its material has refractive index 1.5. If the liquid has refractive index 1.33 the new focal length of the lens is
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a)		+80 cm
b)		-80 cm
c)		-160 cm
d)		-100 cm

18. The focal length of a convex lens depends upon

a)		frequency of the light ray
b)		wavelength of the light ray
c)		both (a) and (b)
d)		none of these

19. A beam of light is partially reflected and partially refracted from a surface. The angle between the reflected and the refracted light is $90^{o}$ . The angle of refraction is $30^{o}$ . Then the angle of incidence must be

a)		$78^{o}$
b)		$50^{o}$
c)		$60^{o}$
d)		$75^{o}$

20. A 9 cm high image of an object is formed on a screen by a convex lens. When the lens is displaced towards the screen, again a 4 cm high image is formed on the screen. The height of the object is

a)		6 cm
b)		6.25 cm
c)		6.5 cm
d)		none of these

21. The refractive index of an equilateral prism is $\sqrt{3}$ . What is the angle of minimum deviation of the prism

a)		$45^{o}$
b)		$37^{o}$
c)		$60^{o}$
d)		$30^{o}$

22. How many images will be formed if two mirrors are fitted on adjacent walls and one mirror on ceiling?

a)		5
b)		7
c)		11
d)		2

23. Plane mirrors A and B are kept at an angle $θ$ with respect to each other. Light falls on A, is reflected then falls on B and is reflected. The emergent ray is opposite to the incident direction. Then angle $θ$ is equal to

a)		$30^{o}$
b)		$60^{o}$
c)		$30^{o}$
d)		$45^{o}$

24. The limit of resolution of the eye is 1 minute. At a distance x from the eye two persons stand with a lateral seperation of 3cm. To see the two persons just resolved by the naked eye, x should be about

a)		20 km
b)		15 km
c)		10 km
d)		30 km

25. The length of a telescope is 100cm and the magnification is 19. The focal length of the objective and eye piece are

a)		90 cm and 10 cm
b)		85 cm and 1cm
c)		80 cm and 20 cm
d)		95 cm and 25 cm

26. In a compound microscope the objective produces a magnification10 and eye piece produces a magnification 5. The overall magnification produced by the compound microscope is

a)		2
b)		5
c)		25
d)		50

27. The colour of the sky is due to

a)		scattering of light
b)		refraction of light
c)		interfernce of light
d)		reflection of light

28. In the displacement method of measuring the focal length of a convex lens, the focal length of the images in the two positions of the lens between the object and the screen is 9cm and 4cm respectively. The focal length of the object is

a)		6.25 cm
b)		3/2 cm
c)		6 cm
d)		36 cm

29. An object is placed at a distance $f / 2$ from a cnvex lens of focal length $f$ . The image will be at

a)		at $\frac{3 f}{2}$ ,real and inverted
b)		at one of the foci, virtual, double the size of the object
c)		at $\frac{f}{2}$ real and inverted
d)		at 2 $f$ virtual and erect

30. The graph shows the variation of the magnification m produced by a convex lens with distance V. What is the focal length of the lens used
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a)		b/c
b)		b/ca
c)		bc/a
d)		c/b

31. Two thin convex lenses of focal length 10cm and 15cm are combined together. The focal length of the combination is

a)		25 cm
b)		12.5 cm
c)		15 cm
d)		6 cm

32. The focal length of a convex lens is minimum for

a)		red
b)		violet
c)		blue
d)		green

33. A biconvex lens of focal length 20cm is cut into two plano-convex lenses. The focal length of each part is

a)		10 cm
b)		20 cm
c)		30 cm
d)		40 cm

34. The minimum distance between the object and its real image formed by a convex lens of focal length $f$ is

a)		1.5 $f$
b)		$f$
c)		4 $f$
d)		3 $f$

35. The refracting angle of a prism is A and the refractive index of the material of the prism is cotA/2, the angle of minimum deviation is

a)		180 - A
b)		180 - 3A
c)		90 - A
d)		180 -2A

36. A ray of light travels from vaccum into a medium of refractive index n. The angle of incidence is found to be twice the angle of refraction. The angle of incidence is then

a)		$\cos^{- 1} n / 2$
b)		${2 \cos}^{- 1} n / 2$
c)		${2 \sin}^{- 1} n$
d)		${2 \sin}^{- 1} n / 2$

37. The refractive index of a prism depends on

a)		angle of the prism
b)		deviation produced by the prism
c)		intensity of light
d)		the wave length of light

38. A fish looking up through water sees the outside world contained in a circular horizon. If the refractive index of water is 4/3 and the fish is 12cm below the surface, the radius of the circle on the surface of water is

a)		$12 \times 3 \times \sqrt{5}$ cm
b)		$12 \times \sqrt{3} \times \sqrt{7}$ cm
c)		$\frac{12 \times 3}{\sqrt{7}}$ cm
d)		$12 \times 3 / 4$ cm

39. It is possible to observe total internal reflection when a ray of light travels from

a)		air to water
b)		air to glass
c)		water to glass
d)		glass to water

40. A concave lens has focal length $f$ . A real object placed at a distance $f$ in front of the lens from the pole produces an image

a)		at infinity
b)		at $f$
c)		at $\frac{f}{2}$
d)		at $\frac{2}{f}$

41. An object placed at a distance a from the focus of a convex lens forms its real image at a distance b from the focus. The focal length of the mirror is

a)		ab
b)		$\sqrt{ab}$
c)		$\frac{a + b}{2}$
d)		a/b

42. The image formed by a plane mirror is

a)		real and same size as the object
b)		virtual, same size as the object
c)		real and magnified
d)		virtual and diminished

43. The distance between a point source of light and screen is doubled. The intensity of light on the screen will be

a)		four times the original value
b)		two times the original value
c)		half the original value
d)		one quarter the original value

44. Light year is the unit of

a)		Distance
b)		Time
c)		force
d)		solar mass

45. From the following which one is used for studying ultra violet light?

a)		prism of crown glass
b)		prism of flint glass
c)		prism of quartz
d)		prism with combination of flint and crown glass

46. The limit of resolution of the eye is one minute at a distance x from the eye. Two persons stand with a lateral separation of 3cms. To see the two persons just resolved by the naked eye, x should be about

a)		20km
b)		15km
c)		10km
d)		30km

47. When light travels from 1 medium to another that remains unaltered is

a)		speed
b)		wave length
c)		frequency
d)		intensity

48. A convex mirror placed at a distance of 20 cm from a candle forms a virtual image at the same position as that formed by a plane mirror at a distance of 12 cm from the candle. What is the focal length of the convex mirror?

a)		20 cm
b)		15 cm
c)		10 cm
d)		5 cm

49. A man under water in a lake is viewing a boy standing on the bank of the lake. Then for him the boy appears to be

a)		shorter
b)		taller
c)		of the same size
d)		16 cm

50. A tank is filled with water upto a height of 12.5 cm. The apparent depth of a needle at the bottom of the tank is (n of water =1.33)

a)		12.5 cm
b)		9.4 cm
c)		16.6 cm
d)		11.17 cm