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14. waves and sound — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysics14. waves and sound1 Mark
MCQ
You are driving in your car listening to music on the radio. Your car is equipped with radio that can recieved radio singals of frequency $(f_1 \approx\, 3\, MHz),$ other of frequency $(f_2 \approx\, 30\, MHz),$ and third of frequency $(f_3 =\, 3\, GHz),$. You enter a tunnel with a circular opening of diameter $10\ m.$ Which kind of radio signal will you be able to receive the longest as you continue to travel in the tunnel ?
  • A
    Radio signal of frequency $f_1$
  • ✓
    Radio signal of frequency $f_2$
  • C
    Radio signal of frequency $f_3$
  • D
    Distance upto which signal can penetrate in tunnel is independent of frequency
✓

Answer

Correct option: B.
Radio signal of frequency $f_2$
b
In the tunnel only diffracted signal will reach and for diffraction size of obstacle must be of order of wavelength

$\mathrm{v}=\mathrm{n} \lambda.$

$\lambda_{1}=100 \mathrm{\,m}, \lambda_{2}=10 \mathrm{\,m} ; \lambda_{3}=.01 \mathrm{\,m}$ therefore $\mathrm{f}_{2}$ will be the frequency.

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