Question

The frequency above which radiation of electrical energy is practical is
A. 0.2kHz
B. 2kHz
C. 20kHz
D. 20Hz

Answer 1

Hint: You could explain the method of production of electric energy by using radiation at atomic level. You could check for the frequency ranges given in the options and hence find the drawbacks of each range. Thereby, find the ideal frequency range for which the radiation of electrical energy is practical.

Complete answer:
In the question, we are asked to find the frequency above which the radiation of electrical energy is considered practical.
So basically the radiation when hit on a metal surface emits electrons from the metal surface and this electron’s flow results in production of electrical energy. We know that energy generally is directly proportional to frequency. So higher the frequency higher is the energy generated. There is a minimum energy required for the electrons to leave the metal surface and the remaining energy is used for the transport. This fact we have learnt from the photoelectric effect.
For the frequencies ranging from 20Hz to 20kHz, the power of the signal is too small for the production electrical energy to be practical. For frequencies higher than 20kHz, the signals could be sent over greater distances over thousands of miles even at less power.
Therefore, for frequencies above 20kHz, the production of electric energy is practical.

Hence, option C is the correct option.

Note:
Electric energy is basically a type of kinetic energy that is caused as a result of movement of electric charges. Amount of electrical energy is known to be directly proportional to the speed of the charges. That is, we could say that faster charges are the greater will be the electric energy possessed by them.