Optics MCQs

Question 1

A screen is placed at a distance 40cm away from an illuminated object. A converging lens is placed between the source and the screen and it is attempted to form the image of the source on the screen. If no position could be found, the focal length of the lens:

Accepted Answer

Must be greater than 10cm

Answer

Must be less than 10cm

Answer

Must not be greater than 20cm

Answer

Must not be less than 10cm.

Question 2

The distance between an object and the screen is 100cm. A lens placed between them produces an image on the screen when the lens is placed at two positions 40cm apart. The power of the lens is nearly:

Accepted Answer

5 diopters

Answer

3 diopters

Answer

7 diopters

Answer

9 diopters

Question 3

A converging lens of focal length f is placed just above a water surface parallel to the surface without touching it. A point source of light S is placed inside the water vertically before the lens at a depth f from it. This arrangement will produce:

Accepted Answer

A virtual image of S in water

Answer

A parallel beam of light converging from the lens

Answer

A real image of S in air

Answer

A virtual image of S in air

Question 4

Light is incident normally on a diffraction grating through which first order diffraction is seen at 32o. The second order diffraction will be seen at:

Accepted Answer

None of these

Answer

84o

Answer

48o

Answer

64o

Question 5

A light source approaches the observer with a velocity of 0.5 cm. Doppler shift for light of wavelength 550 Å is :

Accepted Answer

1833 Å

Answer

616 Å

Answer

5500 Å

Answer

6160 Å

Question 6

The angular width of a central max. is 30o when the slit is illuminated by light of wavelength 6000 Å. Then the width of the slit will be approx.

Accepted Answer

12 x 10^-7 m

Answer

12 x 10^-6 m

Answer

12 x 10^-8 m

Answer

12 x 10^-9 m

Question 7

Doppler shift for the light of wavelength 6000 Å emitted from the sun is 0.04 Å. If the radius of the sun is 7 x 10^8 m then the time period of rotation of the sun will be :

Accepted Answer

25 days

Answer

30 days

Answer

365 days

Answer

24 hours

Question 8

A plane monochromatic light falls normally on a diaphragm with two narrow slits separated by a distance d = 2.5 mm. A fringe pattern is formed on the screen placed at D = 100 cm behind the diaphragm. If one of the slits is covered by a glass plate of thickness 10 m, then the distance by which these fringes will be shifted will be:

Accepted Answer

4 mm

Answer

2 mm

Answer

3 mm

Answer

5 mm

Question 9

A two-slit Young's experiment is done with monochromatic light of wavelength 6000 Å. Slits are 2 mm apart and fringes are observed on a screen placed 10 cm away from the slits. If a transparent plate of thickness 0.5 mm is placed in front of one of the slits, the interference pattern shifts by 5 mm. Then the refractive index of the transparent plate should be:

Accepted Answer

1.2

Answer

1.1

Answer

1.3

Answer

1.5

Question 10

Interference fringes from sodium light (1 = 5890 Å) in a double slit experiment have an angular width of 0.20o. To increase the fringe width by 10%, the wavelength of light used should be:

Accepted Answer

6479 Å

Answer

5892 Å

Answer

4000 Å

Answer

8000 Å

Question 11

A double-slit experiment is immersed in a liquid with a refractive index of 1.33. The separation between the slits is 1.0 mm and the distance between the slit and screen is 1.33 m. If slits are illuminated by a parallel beam of light whose wavelength is 6300 Å, then the fringe width will be:

Accepted Answer

0.63 mm

Answer

6.3 mm

Answer

63 mm

Answer

None of these

Question 12

The ratio of intensities between point A and that of the central fringe is 0.853. The path difference between the two waves at point A will be:

Accepted Answer

λ/8

Answer

λ/2

Answer

λ/4

Answer

λ

Question 13

Two waves of the same intensity produce interference. If intensity at the maximum is 4I, then intensity at the minimum will be:

Accepted Answer

0

Answer

2I

Answer

3I

Answer

4I

Question 14

Light of wavelength λ is incident on a slit. The first minima of the diffraction pattern is found to lie at a distance of 6 mm from the central maximum on a screen placed at a distance of 2 m from the slit. If the slit width is 0.2 mm, then the wavelength of the light used will be:

Accepted Answer

6000 Å

Answer

4000 Å

Answer

7000 Å

Answer

7400 Å

Question 15

The figure shows a double-slit experiment. P and Q are the slits. The path lengths PX and QX are nλ and (n+2)λ respectively, where n is a whole number and λ is the wavelength. Taking the central fringe as zero, what is formed at X:

Accepted Answer

Second bright

Answer

First bright

Answer

First dark

Answer

Second dark

Question 16

Plane polarised light is passed through a polaroid. On viewing through the polaroid, we find that when the polaroid is given one complete rotation about the direction of the light, one of the following is observed :

Accepted Answer

There is no change in intensity

Answer

The intensity of light gradually decreases to zero and remains at zero

Answer

The intensity of light gradually increases to a maximum and remains at maximum

Answer

The intensity of light is twice maximum and twice zero

Question 17

When one of the slits of Young's experiment is covered with a transparent sheet of thickness 4.8 mm, the central fringe shifts to a position originally occupied by the 30th bright fringe. What should be the thickness of the sheet if the central fringe has to shift to the position occupied by the 20th bright fringe?

Accepted Answer

3.2 mm

Answer

3.8 mm

Answer

1.6 mm

Answer

7.6 mm

Question 18

The periodic time of rotation of a certain star is 22 days and its radius is 7 x 10^8 metres. If the wavelength of light emitted by its surface is 4320 Å, the Doppler shift will be: (1 day = 86400 sec)

Accepted Answer

0.033 Å

Answer

0.33 Å

Answer

3.3 Å

Answer

33 Å

Question 19

In a two-slit experiment with monochromatic light, fringes are obtained on a screen placed at some distance from the slits. If the screen is moved by 5 x 10^-2m towards the slits, the change in fringe width is 3 x 10^-5 m. If the separation between the slits is 10-3 m, the wavelength of light used is:

Accepted Answer

6000 Å

Answer

5000 Å

Answer

3000 Å

Answer

4500 Å

Question 20

In a YDSE the separation between the slits is 1 mm and the screen is at a distance of 2 m from the plane of the slits. The wavelength missing on the screen at a point directly in front of one of the slits is:

Accepted Answer

500 nm

Answer

417 nm

Answer

523 nm

Answer

600 nm

Free Optics MCQs with Answers