Question

Assertion :Audio signal of frequency 10 kHz cannot be transmitted over long distance without modulation. Reason: Length of the antenna required $\lambda /4$, should have practical value.

• A. Both Assertion and Reason are correct and Reason is the correct explanation for Assertion
• B. Both Assertion and Reason are correct but Reason is not the correct explanation for Assertion
• C. Assertion is correct but Reason is incorrect
• D. Both Assertion and Reason are incorrect

Answer 1

The correct option is A Both Assertion and Reason are correct and Reason is the correct explanation for Assertion

Frequency of signal $f=10\times {10}^{3}Hz$
Speed of wave $v=3\times {10}^{8}m/s$
Thus wavelength of wave $\lambda =\frac{v}{f}$
$\therefore$ $\lambda =\frac{3\times {10}^8}{10\times {10}^3}=3\times {10}^{4}m$
So, length of antenna required $L=\frac{\lambda }{4}=\frac{30000}{4}=7500m$
It is practically impossible to have an antenna of length $7.5km$. So it is impossible to transmit 10 kHz frequency over long distance without modulation.
Hence option A is correct.