A monoenergetic (18 keV) electron beam initially in the horizontal direction is subjected to a horizontal magnetic field of 0.04 G normal to the initial direction. Estimate the up or down deflection of the beam over a distance of 30 cm (me `= 9.11 × 10^(–31) kg)`. [Note: Data in this exercise are so chosen that the answer will give you an idea of the effect of earth’s magnetic field on the motion of the electron beam from the electron gun to the screen in a TV set.]

Explanation

To solve the problem of estimating the deflection of a monoenergetic electron beam in a magnetic field, we will follow these steps:

### Step 1: Convert Energy to Joules
The energy of the electron beam is given as 18 keV. We need to convert this energy into joules.

\[ \text{Energy (in Joules)} = 18 \, \text{keV} \times 1.6 \times 10^{-19} \, \text{J/eV} = 18 \times 10^3 \times 1.6 \times 10^{-19} \, \text{J} \]
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