A simple and common technique for accelerating electrons is shown in Figure 18.5

Question

A simple and common technique for accelerating electrons is shown in Figure 18.55, where there is a uniform electric field between two plates. Electrons are released, usually from a hot filament, near the negative plate, and there is a small hole in the positive plate that allows the electrons to continue moving. (a) Calculate the acceleration of the electron if the field strength is 2.50×104 N/C . (b) Explain why the electron will not be pulled back to the positive plate once it moves through thehole.?

Explanation / Answer

The expression you will use is the following:

a = F/m and F = qE so:

a = qE / m    where m is the mass of the electron = 9.11x10-31 kg; and q = 1.6x10-19 C

a = 1.6x10-19 C * 2.5x104 N/C / 9.11x10-31 kg

a = 4.39x1015 m/s2

For part b) this is Probably because there is no field beyond the positive plate.

Hope this helps

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