How do you calculate frequency of light?

Hint:In general terms frequency is the measure of a repeating event with respect to time. In case of light Frequency is defined as the number of cycles of light(photons) passing through a point in a unit of time. Light is an Electromagnetic wave which shows Dual Nature and hence we have multiple ways to solve questions regarding a Light wave

Complete solution:
There is more than one way to calculate the frequency of light, It all depends on what are the given quantities.

First we need to analyze what are the terms given to us in the question, for that read the question and write down all the values given in the question.

For example, if we are asked to find the frequency of a light wave of energy $3.97\times {{10}^{-15}}$ Joules.

Here Energy is given and we need to find the frequency of light, for this we will use the formula
$E=h\nu $
Write down the given values in the formula
We have E=$3.97\times {{10}^{-15}}$ Joules.
Where h is known as planck's constant having value $6.626\times {{10}^{-34}}$ Joules per second
So, $E=h\nu $ or,
$\nu = \dfrac{h}{E}$

Putting the values in the above equation, we get
$\nu = \dfrac{6.626\times {{10}^{-34}}J{{s}^{-1}}}{3.97\times {{10}^{-15}}J}$
Here $J{{s}^{-1}}$stands for Joules per second.

Now by solving the above equation we will get our required answer
$\nu = \dfrac{6.626}{3.97}\times {{10}^{-34+15}}{{s}^{-1}}$

By solving this we will get $\nu =6\times {{10}^{18}}$per second or,
$\nu =6\times {{10}^{18}}$Hertz.

Conclusion,
Hence, Frequency of light is $\nu =6\times {{10}^{18}}$ Hertz.

Note:
There are many ways to find a Frequency of a Light wave Depending upon what are the given quantities,
Alternative method: If we have been given a wavelength of light and asked for the frequency then we need to follow this Formula.
 $c=\dfrac{\lambda }{v}$