First slide

Doppler

Question

The frequency of a radar is 780 MHz. The frequency of the reflected wave from an aeroplane is increased by 2 .6 kHz. The velocity of aeroplane is

Moderate

A

0 .25 km/se
B

0.5 km/sec
C

1 km/sec
D

2 km/sec

Solution

See questiotr (08).
$n^{'} - n^{''} = Δ n = \frac{2 V_{s}}{V} \times n Δ n = 2 \cdot 6 k H z = 2 \cdot 6 \times 10^{3} H z and n = 780 M H z = 780 \times 10^{6} H z ∴ 2 \cdot 6 \times 10^{3} = \frac{2 V_{S}}{3 \times 10^{8}} \times 780 \times 10^{6} or v_{s} = \frac{(2 \cdot 6 \times 10^{3}) (3 \times 10^{8})}{2 \times (780 \times 10^{6})} = 500 m / s = 0 \cdot 5 k m / s e c$

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