Question

In the inside of a TV set an electron is accerlerated by a potential difference of 20 kV in an evacuated tube. It is then passed through an uniform magnetic field of 100 mT which deflects it to the desired position on the screen.

1) Draw a diagram showing the path of the electron as it passes from the electron source to the screen.

2) After passing through the accelerating potential, what is the kinetic energy of the electron in eV? In joules?

3) What is the speed of the electron just before it enters the magnetic deflecting field?

4) What will be the radius of curvature of its path in the field?

Answer 1

PART (1):

Electron will follow a helical path:

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PART (2):

Potential difference, V = 20 kV = 20000 V

Hence, Energy of electron = (1 e) x (20000 V) = 20000 eV

We have, 1 eV = 1.602 x 10^-19 J

Therefore, Kinetic energy of electron = 20000 eV x 1.602 x 10^-19 J

= 3.204 x 10^-15 J

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PART (3):

We have, K.E = 1/2 mv²

Therefore, Speed of the electron is given by:

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PART (4):

Radius of curvature of path is given by:

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