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Wave Optics

Question
CBSEENPH12039480
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A train is moving on a straight track with speed 20 ms-1 .It is blowing its whistle at the frequency of 1000 Hz. The percentage change in the frequency heard by a person standing near the track as the train passes him is (speed of sound = 320 ms-1 ) close to :

  • 6%

  • 12%

  • 18%

  • 24%

Solution

B.

12%

Apparent frequency heard by the person before crossing the train.
straight f subscript 1 space equals space open parentheses fraction numerator straight c over denominator straight c minus straight v subscript straight s end fraction close parentheses space straight f subscript straight o space equals space open parentheses fraction numerator 320 over denominator 320 minus 20 end fraction close parentheses space 1000
Similarly, apparent frequency heard, after crossing the trainsstraight f subscript 2 space equals space open parentheses fraction numerator straight c over denominator space straight c plus straight V subscript straight s end fraction close parentheses straight f subscript straight o space equals space open parentheses fraction numerator 320 over denominator 320 plus 20 end fraction close parentheses 1000 left square bracket straight c space equals speed space of space sound right square bracket increment straight f space equals space straight f subscript 1 minus straight f subscript 2 space equals space open parentheses fraction numerator 2 cv over denominator straight c squared minus straight v subscript straight s superscript 2 end fraction close parentheses straight x space straight f subscript straight o or space fraction numerator increment straight f over denominator straight f subscript straight o end fraction straight x 100 space equals space open parentheses fraction numerator 2 cv over denominator straight c squared minus straight v subscript straight s superscript 2 end fraction close parentheses straight x 100 space equals space fraction numerator 2 space straight x space 320 space straight x space 20 over denominator 300 space straight x space 340 end fraction straight x 100 equals space fraction numerator 2 space space straight x space 32 space straight x space 20 over denominator 3 space straight x 34 end fraction space equals space 12.54 space equals space 12 percent sign

Some More Questions From Wave Optics Chapter

Which of the following frequencies will be suitable for beyond-the-horizon communication using sky waves?

Frequencies in the UHF range normally propagate by means of

Digital signals
(i)    do not provide a continuous set of values,
(ii)    represent values as discrete steps,
(iii)    can utilize binary system, and
(iv)    can utilize decimal as well as binary systems.
Which of the above statements are true?

What is space wave propagation?

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