To observed diffraction, the size of the obstacle

• should be much larger than the wavelength

• has no relation to wavelength

• should be of the order of wavelength

• should be $\frac{\mathrm{\lambda }}{2}$ where λ is the wavelength

In Young's double slit experiment, the source is white light. One slit is covered with red filter and the other with blue filter. There shall be

• alternate red and blue fringes

• alternate dark and pink fringes

• alternate dark and yellow fringes

• no interference

Light of wavelength 600 nm is incident normally on a slit of width 0.2 mm. The angular width of central maxima in the diffraction pattern is (measured from minimum to minimum)

• 6 × 10^-3 rad

• 4 × 10^-3 rad

• 2.4 × 10^-3 rad

• 4.5 × 10^-3 rad

104.

According to Huygens' principle, during refraction of light from air to a denser medium

• Wavelength decreases but speed increases

• Wavelength increases but speed decreases

• Wavelength and speed increases

• Wavelength and speed decreases

In a system of two crossed polarisers, it is found that the intensity of light from the second polariser is half from that of first polariser. The angle between their pass axes is

• 60°

• 30°

• 0°

• 45°

In Young's double-slit experiment, if yellow light is replaced by blue light, the interference fringes becomes

• darker

• brighter

• wider

• narrower

When one of the slits of Young's experiment is covered with a transparent sheet of thickness 4·8 mm, the central shifts to a position originally occupies 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 20th bright fringe ?

• 1.6 mm

• 3.8 mm

• 3.2 mm

• 7.6 mm

In Young's double slit experiment, the central bright fringe can be identified

• as it is narrower than other bright fringes

• by using white light instead of monochromatic light

• as it has a greater intensity than other bright fringes

• as it is wider than other bright fringes

The intensity at the maximum in a Young's double slit experiment is I_o. Distance between two slits is d = , where  is the wavelength of light used in the experiment. What will be the intensity infront  of one of the slits on the screen placed at a distance D = 10 d?

• 

• 3

• 
• 

A siren emitting a sound of frequency 800 Hz moves away from an observer towards a cliff at a speed of 15 m/s. Then, the frequency of sound that the observer hears in the echo reflected from the cliff is (Take, velocity of sound in air = 330 m/s)

• 800 Hz

• 838 Hz

• 885 Hz

• 885 Hz