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## Homework Statement

In a picture tube (eg. a TV set) electrons are accelerated of an electric field. If the electric field strength is 100 kV / m and the electrons travel a distance 0.2 m from rest, what speed will they achieve?

## Homework Equations

E=U/d where E is electric field intensity, U is the voltage and d is the distance.

W=qU

F=qE

(mv^2)/2 = kinetic energy

## The Attempt at a Solution

I think that the potential electrical energy of the electron will be converted into kinetic energy. Hence:

W=qU=(mv^2)/2 or v=sqrt((2qU)/m). The charge and mass of an electron is known and so is the electrical field intensity. If I insert these values in the equation above I will get:

sqrt((2*1.602*10^(-19)*100*10^3)/9.11*10^(-31))=1.87..*10^8 m/s. The correct answer is 8*10^7 m/s.