The amplitude modulated (AM) radio wave bends appreciably round the corners of a 1m × 1m board but the frequency modulated (FM) wave only negligibly bends. If the average wavelengths of AM and FM waves are \(\lambda_a\) and \(\lambda_f\),

1. \(\lambda_a\) > \(\lambda_f\)

2. \(\lambda_a\) = \(\lambda_f\)

3. \(\lambda_a\) < \(\lambda_f\)

4. we don't have sufficient information to decide about the relation of \(\lambda_a\) and \(\lambda_f\)

Which of the following sources gives the best monochromatic light?
1. a candle
2. a bulb
3. a mercury tube
4. a laser

The wavefronts of a light wave travelling in vacuum are given by \(x+y+z=c\). The angle made by the direction of propagation of light with the X-axis is:
1. \(0^{\circ}\)
2. \(45^{\circ}\)
3. \(90^{\circ}\)
4. \(\mathrm{cos^{-1}\left(\frac{1}{\sqrt{3}}\right )}\)

The wavefronts of light coming from a distant source of unknown shape are nearly:
1. plane
2. elliptical
3. cylindrical
4. spherical

The inverse square law of intensity (i.e., the intensity \(\propto \frac{1}{r^2}\)) is valid for:
1. a point source
2. a line source
3. a plane source
4. a cylindrical source

Two sources are called coherent if they produce waves:

When a drop of oil is spread on a water surface, it displays beautiful colours in daylight because of:

Two coherent sources of different intensities send waves which interfere. The ratio of maximum intensity to the minimum intensity is \(25.\) The intensities of the sources are in the ratio:
1. \(25:1\)
2. \(5:1\)
3. \(9:4\)
4. \(625:1\)

The slits in a Young's double-slit experiment have equal width and the source is placed symmetrically with respect to the slits. The intensity at the central fringe is \(I_0.\) If one of the slits is closed, the intensity at this point will be:
1. \(I_0\)
2. \(I_0/4\)
3. \(I_0/2\)
4. \(4I_0\)

A thin transparent sheet is placed in front of a Young's double-slit. The fringe-width will:
1. increase
2. decrease
3. remain same
4. become nonuniform