The near point of distinct vision is at 1 m for an elderly person. What power of lens is to be used to bring the near point to the minimum distance of distinct vision (25 cm)?

• 2.5 D

• 3 D

• 3.5 D

• 4 D

In a Young's double slit experiment the intensity of light when slit is at distance A from central is I. What will be the intensity at the distance of slit is $\frac{\mathrm{\lambda }}{6}$?

• $\frac{\mathrm{I}}{6}$

• $\frac{\mathrm{I}}{12}$

• $\frac{3}{4}\mathrm{I}$

• $\frac{\mathrm{I}}{6}$

Polaroid glass is used in sun glasses because

• it reduces the light intensity to half on account of polarisation

• it is fashionable

• it has good colour

• it is cheaper

In a Young's double slit experiment the spacing between the slits is 0.3 mm and the screen is kept at a distance of 1.5 m. The second bright fringe is found 6 mm from the central fringe. The wavelength of the light used in the experiment is

• 625 nm

• 600 nm

• 550 nm

• 500 nm

Assertion: When light ray is incident at polarising angle on glass, refracted light is partially polarised. 

Reason:  The intensity of light decreases in polarisation.

• If both assertion and reason are true and reason the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

156.

Assertion: A laser beam of 0.2 W power can drill holes through a metal sheet, whereas a 1000 W torch-light cannot. 

Reason: The frequency of laser light is much higher than that of torch light.

• If both assertion and reason are true and reason is the correct explanation of assertion.

• If both assertion and reason are true but reason is not the correct explanation of assertion.

• If assertion is true but reason is false.

• If both assertion and reason are false.

In Young's double slit experiment, fringe order is represented by m, then fringe width is

• Independent of m

• Directly proportional to m

• Directly proportional to ( 2m + 1 )

• Inversely proportional to (2m + 1 )

A light ray is incident on a glass slab, it is partially reflected and partially transmitted. Then the reflected ray is

• completely polarised and highly intense.

• partially polarised and poorly intense.

• partially polarised and highly intense.

• completely polarised and poorly intense.

In an interference, the intensity of two interfering waves are  I  and  4I  respectively. They produce intensity at two points A and B with phase angle of  $\raisebox{1ex}{$\mathrm{\pi }$}\!\left/ \!\raisebox{-1ex}{$2$}\right.$ and  $\mathrm{\pi }$ respectively. Then difference in between them is

• I

• 2 I

• 4 I

• 5 I

In a single slit diffraction with k = 500 nm and lens of diameter 0.1 mm then width of central maxima, obtain on screen at a distance of 1 m will be

• 5 mm

• 1 mm

• 10 mm

• 2.5 mm