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An observer is moving with half the speed of light towards a stationary microwave source emitting waves at frequency 10 GHz. What is the frequency of the microwave measured by the observer ? (speed of light = 3 × 10 8 ms –1 )

1. 10.1 GHz
2. 12.1 GHz
3. 17.3 GHz
4. 15.3 GHz

Correct answer: 17.3 GHz

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