In Thomson.s experiment, prove that the ratio of charge to the mass (e/m) of an electron is given by :
`(e)/(m)=(1)/(2V).(E^(2))/(B^(2))`
where the terms have their usual meaning.

Explanation

To prove the ratio of charge to mass (e/m) of an electron in Thomson's experiment, we can follow these steps:

### Step 1: Understand the Forces Acting on the Electron
In Thomson's experiment, an electron moves through both an electric field (E) and a magnetic field (B). When the electron moves without deflection, the electric force acting on it is equal to the magnetic force.

### Step 2: Write the Expression for Electric Force
The electric force (F_E) acting on the electron can be expressed as:
\[ F_E = eE \]
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