# physics

How strong an electric field is needed to accelerate electrons in a TV tube from rest to one-tenth the speed of light in a distance of 4.9 cm ?

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1. Require that

Work done by E-field = Kinetic Energy gain

e*E*X = (1/2) m V^2 = (1/200) m c^2

E = (1/200)(m/e)c^2/X
where X = 0.049 m
m = 9.11*10^-31 kg
e = 1.602*10^-19 C
c = 3.00*10^8 m/s

E = 52200 V/m

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2. The electrons move with a velocity of 3.0x10^6 m/s. What electric field strength is needed to accelerate electrons from rest to this velocity in a distance of 9.0 mm?

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