When the accelerating voltage in a CRT is 500 V and the deflecting voltage is 15 V,?

Question

When the accelerating voltage in a CRT is 500 V and the deflecting voltage is 15 V, the beam deflection is 1.2 cm on the screen. If the accelerating voltage is changed to 750 V and the deflecting voltage is changed to 45 V, what will the deflection be?

Answer: 2.4 cm

Answer 1

The answer is correct, here's how you get it:

The deflection is directly proportional to the ratio of the deflecting voltage to the accelerating voltage.

Here the ratio = 15/500 = 0.03

(This is because if you multiply all voltages by some factor, say 1.5, the result is the same. The CRT is basically a linear device.)

You will get the same deflection of 1.2 cm for voltages of 22.5v and 750v

ratio = 22.5/750 = 0.03

The deflection is also directly proportional to the deflecting voltage.

Now double the deflecting voltage from 22.5v to 45v, the deflection will double from 1.2 cm to 2.4 cm.