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

12th Standard

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Physics

Time : 00:20:00 Hrs
Total Marks : 20

20 x 1 = 20
1. A rod of length 10 cm lies along the principal axis of a concave mirror of focal length 10 cm in such a way that its end closer to the pole is 20 cm away from the mirror. The length of the image is,

(a)

2.5 cm

(b)

5cm

(c)

10 cm

(d)

15cm

2. The radius of curvature of curved surface at a thin planoconvex lens is 10 cm and the refractive index is 1.5. If the plane surface is silvered, then the focal length will be,

(a)

5cm

(b)

10 cm

(c)

15 cm

(d)

20 cm

3. Two coherent monochromatic light beams of intensities I and 4I are superposed. The maximum and minimum possible intensities in the resulting beam are

(a)

5I and I

(b)

5I and 3I

(c)

9I and I

(d)

9I and 3I

4. First diffraction minimum due to a single slit of width 1.0×10–5 cm is at 30o. Then wavelength of light used is,

(a)

400 $\mathring { A }$

(b)

500 $\mathring { A }$

(c)

600 $\mathring { A }$

(d)

700 $\mathring { A }$

5. One of the of Young’s double slits is covered with a glass plate as shown in figure. The position of central maximum will,

(a)

get shifted downwards

(b)

get shifted upwards

(c)

will remain the same

(d)

data insufficient to conclude

6. The transverse nature of light is shown in,

(a)

interference

(b)

diffraction

(c)

scattering

(d)

polarisation

7. If an object moves towards a plane mirror with a speed V at an angle θ to the perpendicular to the plane of the mirror,find the relative velocity between the object and the image,

(a)

V

(b)

2V

(c)

2 V cosθ

(d)

2 V sin θ

8. Convergence of concave mirror can be decreased by dipping in

(a)

Water

(b)

Oil

(c)

Both

(d)

None ofthese

9. An object 2.5 crn high is placed at a distance of 10 cm from a concave mirror of radius of curvature 30 cm. The size of the image is

(a)

9.2 cm

(b)

10.5 cm

(c)

5.6 cm

(d)

7.5 cm

10. A concave mirror of focal length 15 cm forms an image having twice linear dimensions of the object. The position of the object when the image is virtual will be

(a)

22.5 cm

(b)

7.5 cm

(c)

7.5 cm

(d)

45 cm

11. The minimum distance between the object and its real image for concave mirror is

(a)

(b)

2f

(c)

4f

(d)

Zero

12. An object is placed, 40 cm from a concave mirror of focal length 20 cm, the image formed is,

(a)

Real, inverted and same in size

(b)

Real, inverted and smaller

(c)

Virtual, erect and larger

(d)

Virtual, erect and smaller

13. Which of the following forms a virtual and erect image for all position of the object.

(a)

Convex lens

(b)

Concave lens

(c)

Convex mirror

(d)

both b & c

14. Radius of curvature of convex mirror is 40 cm and the size of object is twice as that of image than the image distance is

(a)

10 cm

(b)

20 cm

(c)

40 cm

(d)

30 cm

15. An object 5 cm tall is placed 1m from concave spherical mirror which has a radius of curvature of 20 cm. The size of the image is

(a)

0.11 cm

(b)

0.50 cm

(c)

0.55 cm

(d)

0.60 cm

16. A dentist uses a small mirror that gives a magnification of 4 when it is held 0.60 cm from a tooth. The radius of curvature of the mirror is

(a)

1.60 cm (convex

(b)

0.8 cm (concave)

(c)

1.60 cm (concave)

(d)

0.8 cm (convex)

17. A convex mirror of focal length 10 cm forms an image which is half of the size of the object. The distance of the object from the mirror is

(a)

10 cm

(b)

20 cm

(c)

5 cm

(d)

15 cm

18. A rear mirror of a vehicle is cylindrical having radius of curvature 10 cm. The length of arc of curved surface is also 10 cm. If the eye of driver is assumed to be at large distance, from the mirror, then the field of view in radian is

(a)

0.5

(b)

1

(c)

2

(d)

4

19. A cube of side 2m is placed in front of a concave mirror focal length 1m with its face P at a distance of 3m and face Q at a distance of 5m from the mirror. The distance between the images of face P and Q and height of images P and Q are

(a)

1m, O.5m,0.25m

(b)

0.5m, 1m, 0.25m

(c)

0.5 m, 0.25m, 1m

(d)

0.025m, 1m, 0.5m

20. A concave mirror forms an image of sun at a .distance of 12 ern from it

(a)

The radius of curvature of this mirror is 6 cm

(b)

To use it as a shaving mirror, it must be held at a distance of 8 - 10 cm from the face

(c)

If an object is kept at a distance of 12 cm from it, the image formed will be same size as the object

(d)

All the above