The electron beam inside an old television picture tube is 0.40 mm in diameter a

Question

The electron beam inside an old television picture tube is 0.40 mm in diameter and carries a current of 50 A. This electron beam impinges on the inside of the picture tube screen.

Part B

What is the current density in the electron beam?

Express your answer with the appropriate units.(J=?)

Part C

The electrons move with a velocity of 3.0 ×107 m/s. What electric field strength is needed to accelerate electrons from rest to this velocity in a distance of 5.0 mm?

Express your answer with the appropriate units.(E=?)

Part D

Each electron transfers its kinetic energy to the picture tube screen upon impact. What is the power delivered to the screen by the electron beam?

Express your answer with the appropriate units.(P=?)

Explanation / Answer

B) current density is J = i/A = (50*10^-6)/(3.142*(0.2*10^-3)^2) = 397.83 A/m^2

C) W = F*S = change in kinetic energy

Force F = q*E

then q*E*S = 0.5*m*(v^2-u^2)

q and m are the charge and mass of the electron

1.6*10^-19*E*5*10^-3 = 0.5*9.11*10^-31*(3*10^7)^2

E = 5.12*10^5 N/C

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D) Power delivered is P =dV*I = E*d*I = 5.12*10^5*5*10^-3*50*10^-6 = 0.128 W

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