Question

(a) Name the e.m. waves which are suitable for radar systems used in aircraft navigation. Write the range of frequency of these waves.

(b) If the Earth did not have atmosphere, would its average surface temperature be higher or lower than what it is now? Explain.

(c) An e.m. wave exerts pressure on the surface on which it is incident. Justify.

OR

(a) "If the slits in Young's double slit experiment are identical, then intensity at any point on the screen may vary between zero and four times to the intensity due to single slit".

Justify the above statement through a relevant mathematical expression.

(b) Draw the intensity distribution as function of phase angle when diffraction of light takes place through coherently illuminated single slit.

Answer 1

(a) Microwaves are suitable for the radar system used in aircraft navigation.

Range of frequency of microwaves is 108 Hz to 1011 Hz.

(b) If the Earth did not have atmosphere, then there would be absence of greenhouse effect of the atmosphere. Due to this reason, the temperature of the earth would be lower than what it is now.

(c) An e.m. wave carries momentum with itself and given by 

P = Energy of wave(U)/ Speed of the wave(c)

= U/c

when it is incident upon a surface it exerts pressure on it.

OR

(a) The total intensity at a point where the phase difference is ∅, is given by \(I=I_1+I_2+2\sqrt{I_1I_2}\) COS ∅. Here I₁ and I₂ are the intensities of two individual sources which are equal.

When ∅ is 0, I = 4I₁.

When ∅ is 90°, I = 0

Thus intensity on the screen varies between 4I₁ and 0.

(b) Intensity distribution as function of phase angle, when diffraction of light takes place through coherently illuminated single slit