The energies $E_1$ and $E_2$ of two radiations are $25 \ eV$ and $50 \ eV$ respectively. The relation between their wavelengths,i.e.,$\lambda_1$ and $\lambda_2$,will be:

With regard to the photoelectric effect,identify the correct statement among the following.

Given below are two statements about $X$-ray spectra of elements :
Statement $(I) :$ $A$ plot of $\sqrt{\nu}$ ($\nu =$ frequency of $X$-rays emitted) vs atomic mass is a straight line.
Statement $(II) :$ $A$ plot of $\nu$ ($\nu =$ frequency of $X$-rays emitted) vs atomic number is a straight line.
In the light of the above statements choose the correct answer from the options given below :

The wavelength of $X$-ray is $1.5 \times 10^{-10} \ m$. Find the frequency.

If light waves pass through a $Nicol$ prism,then all the oscillations occur only in one plane. Such a beam of light is called:

The laser in an audio compact disc uses light of wavelength $7.8 \times 10^2 \ nm$. What is the frequency of light emitted by the laser?