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#### 12th Standard Physics Optics English Medium Free Online Test One Mark questions 2020 - 2021

12th Standard EM

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Physics

Time : 00:20:00 Hrs
Total Marks : 20
20 x 1 = 20
1. The speed of light in an isotropic medium depends on,

(a)

its intensity

(b)

its wavelength

(c)

the nature of propagation

(d)

the motion of the source w.r.t medium

2. An object is placed in front of a convex mirror of focal length of f and the maximum and minimum distance of an object from the mirror such that the image formed is real and magnified.

(a)

2f and c

(b)

c and $\infty$

(c)

f and O

(d)

None of these

3. When a biconvex lens of glass having refractive index 1.47 is dipped in a liquid, it acts as a plane sheet of glass. This implies that the liquid must have refractive index,

(a)

less than one

(b)

less than that of glass

(c)

greater than that of glass

(d)

equal to that of glass

4. An air bubble in glass slab of refractive index 1.5 (near normal incidence) is 5 cm deep when viewed from one surface and 3 cm deep when viewed from the opposite face. The thickness of the slab is,

(a)

8 cm

(b)

10 cm

(c)

15 cm

(d)

20 cm

5. A plane glass is placed over a various coloured letters (violet, green, yellow, red) The letter which appears to be raised more is,

(a)

red

(b)

yellow

(c)

green

(d)

violet

6. In a Young’s double-slit experiment, the slit separation is doubled. To maintain the same fringe spacing on the screen, the screen-to-slit distance D must be changed to,

(a)

2D

(b)

$\frac{D}{2}$

(c)

$\sqrt{2}$D

(d)

$\frac{D}{\sqrt2}$

7. When light is incident on a soap film of thickness 5×10–5 cm, the wavelength of light reflected maximum in the visible region is 5320 Å. Refractive index of the film will be,

(a)

1.22

(b)

1.33

(c)

1.51

(d)

1.83

8. A ray of light strikes a glass plate at an angle 60o. If the reflected and refracted rays are perpendicular to each other, the refractive index of the glass is,

(a)

$\sqrt3$

(b)

$\frac{3}{2}$

(c)

$\sqrt{\frac{3}{2}}$

(d)

2

9. Light transmitted by Nicol prism is,

(a)

partially polarised

(b)

unpolarised

(c)

plane polarised

(d)

elliptically polarised

10. Two plane mirrors are at 45° to each other. If an object is placed between them than the number of images will be

(a)

5

(b)

9

(c)

7

(d)

8

11. A man runs towards a mirror at a speed 15m/s. The speed of the image relative to the man is

(a)

15 rns-1

(b)

30 ms-1

(c)

35 ms-1

(d)

20 ms-1

12. Two plane mirror are at right angles to each other. A man stands between them and combs hair with his right hand. In how many of the images will he be seen using his right hand.

(a)

None

(b)

1

(c)

2

(d)

3

13. A plane mirror produces a magnification of

(a)

-1

(b)

+ 1

(c)

Zero

(d)

Between 0 and + ∞

14. What should be the angle between two plane mirror so that whatever be the angle of incidence, the incident ray and the reflected ray from the two mirrors be parallel to each other

(a)

60°

(b)

90°

(c)

120°

(d)

175°

15. It is desired to photograph the image of an object placed at a distance of 3m from the plane mirror. The camera which is at a distance of 4.5 m from the mirror should be focused for a distance of

(a)

3 m

(b)

4.5 m

(c)

6 m

(d)

7.5 m

16. Two plane mirrors A and Bare aligned parallel to each other, as shown in the figure. A light ray is incident at an angle of 30° at a point just inside one end of A. The plane of incidence coincides with the plane of the figure. The maximum number of times the ray undergoes reflections (including the first one) before it emerges out is)

(a)

28

(b)

30

(c)

32

(d)

34

17. The figure shows two rays A and B being reflected by a mirror and going as 'A' and 'B' the mirror is

(a)

plane

(b)

concave

(c)

convex

(d)

may be any spherical mirror

18. Figure shows a cubical room ABCD will the wall CD as plane mirror. Each side of the room is 3m We placed a camera at the midpoint of the wall AB. At what distance should the camera be focussed to photograph an object placed at

(a)

1.5 m

(b)

3m

(c)

6 m

(d)

more than 6 m

19. In an experiment of find the focal length of a concave mirror a graph is drawn between the magnitudes of u and V. the graph looks like

(a)

(b)

(c)

(d)

20. The image formed by a convex mirror of a real object is larger than the object

(a)

when μ <21

(b)

when μ > 2f

(c)

for all values of μ

(d)

for no value of μ