KVPY 2020-21 SB SX Exam Previous Papers

Question : 35 of 120

Marks: +1, -0

The intensity of light from a continuously emitting laser source operating at 638 nm wavelength is modulated at 1 GHz. The modulation is done by momentarily cutting the intensity off with a frequency of 1 GHz. What is the farthest distance apart two detectors can be placed in the line of the laser light, so that they can see the portions of the same pulse simultaneously? (Consider the speed of light in air

3 ×10^8

m/s) :-

30 µm
30 cm
3m
30 m

Validate

Solution:

Time period between two flashes

={1}/{{f}}

Distance travelled by laser in this interval

={{c}}/{{f}}={3 \×10^{8}}/{10^{9}}=0.3 {m}=30 {cm}

So this is the maximum distance between two detectors, so that they can see the same pulse simultaneously.

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