Cellular phones use radio waves to transmit voice communication in the . . . . . . band.

Arrange the following in the ascending order of wavelength $(\lambda) :$
$(A)$ Microwaves $(\lambda_1)$
$(B)$ Ultraviolet rays $(\lambda_2)$
$(C)$ Infrared rays $(\lambda_3)$
$(D)$ $X-$rays $(\lambda_4)$
Choose the most appropriate answer from the options given below $:-$

If an electron oscillates at a frequency of $1 \, GHz$,it emits:

The following table presents parts of the electromagnetic spectrum and their corresponding major applications.

Part of the electromagnetic spectrum	Applications
$P$. Microwave	$I$. For purifying the water
$Q$. $UV$ rays	$II$. For warming the food
$R$. Gamma rays	$III$. For $AM$ and $FM$ communication systems
$S$. Radio wave	$IV$. For treating the cancer cells

The correct option is:

The frequencies of $\gamma$-rays,$X$-rays,and ultraviolet radiations are $B, A,$ and $C$ respectively. Which of the following relations is correct?

If a source of $4 \ kW$ power emits $10^{20}$ photons/second,then this radiation belongs to which part of the electromagnetic spectrum?