61.

A single slit  of width d is illuminated by violet light of wavelength 400 nm and the width of the diffraction pattern is measured as y. When half of the slit width is covered and illuminated by yellow light of wavelength 600 nm, the wdth of the diffraction pattern is

• the pattern vanishes and the width is zero

• y/3

• 3y

• None of the above

When unpolarised light beam is incident from air onto glass (n = 1.5) at the polarising angle

• reflected beam is polarised 100 percent

• reflected and refracted beams are partially polarised

• the reason for (a) is that almost all the light is reflected

• all of the above

The width of the diffraction band varies 

• inversely as the wavelength

• directly as the width of the slit

• directly as the distance between the slit and the screen

• inversely as the size of the source from which the slit is illuminated

An unpolarised beam of intensity I₀ is incident on a pair of nicols making an angle of 60° with each other. The intensity of light emerging from the pair is

• I₀

• I₀/2

• I₀/4

• I₀/8

A beam of light of wavelength 600 nm from a distant source falls on a single slit 1 mm wide and the resulting diffraction pattern is observed on a screen 2 m away. The distance between the first dark fringes on either side of the central bright fringe is

• 1.2 cm

• 1.2 mm

• 2.4 cm

• 2.4 mm

Light from two coherent sources of the same amplitude A and wavelength λ, illuminates the screen. The intensity of the central maximum is I₀. If the sources were incoherent, the intensity at the same point will be

• 4I₀

• 2I₀

• I₀

• $\frac{{\mathrm{I}}_0}{2}$

In Young's double slit experiment with sodium vapour lamp of wavelength 589 nm and the slits 0.589 mm apart, the half angular width of the central maximum is

• sin^-1 (001)

• sin^-1 (0.0001)

• sin^-1 (0.001)

• sin^-1 (0.1)

A single slit Fraunhofer diffraction pattern is formed with white light. For what wavelength of light the third secondary maximum in the diffraction pattern coincides with the second secondary maximum in the pattern for red light of wavelength 6500 $\stackrel{\circ }{\mathrm{A}}$ ?

• $4400 \stackrel{\circ }{\mathrm{A}}$

• $4100 \stackrel{\circ }{\mathrm{A}}$

• $4642.8 \stackrel{\circ }{\mathrm{A}}$

• $9100 \stackrel{\circ }{\mathrm{A}}$

The head lights of a jeep are 1.2 m apart. If the pupil of the eye of an observer has a diameter of 2 mm and light of wavelength 5896 $\stackrel{\circ }{\mathrm{A}}$ is used, what should be the maximum distance of the jeep from the observer if the two head lights are just separated ?

• 33.9 km

• 33.9 m

• 3.34 km

• 3.39 m

When the angle of incidence is 60° on the surface of a glass slab, it is found that the reflected ray is completely polarised. The velocity of light in glass is

• $\sqrt{2} \times {10}^8 {\mathrm{ms}}^{-1}$

• $\sqrt{3} \times {10}^8 {\mathrm{ms}}^{-1}$

• 2 × 10⁸ ms^-1

• 3 × 10⁸ ms^-1