Electrons in a TV picture tube are accelerated from rest by an electric field th

Question

Electrons in a TV picture tube are accelerated from rest by an electric field through a potential difference of 2.65 kV. In contrast to an oscilloscope, where the electron beam is deflected by an electric field, in a TV or computer monitor the beam is deflected by a magnetic field:

a.) What is the speed of the electrons? (v=3.05x10^7; confirmed)

b.) The beam is deflected by a perpendicular magnetic field of magnitude 0.720 T. What is the magnitude of the acceleration of the electrons while in the field? (a=3.86x10^18; confirmed)

c.) What is the speed of the electrons after they travel 4.55 mm through the magnetic field?

If I could visualize what is going on I would be able to use kinematics or conservation of energy to solve this.. I have tried a few things based on examples in my book but none of them work.

Answers so far: 1.) 1.86x10^8 2.) 1.325x10^3

Explanation / Answer

a) gain in KE = -q V

m v^2 / 2 = + e V

9.109 x 10^-31 x v^2 /2 =1.6 x 10^-19 x 2.65 x 10^3

v = 3.05 x 10^7 m/s

b) magnetic force, Fb = q v B

a = Fb / m = q v B / m

a = (1.6 x 10^-19 x 3.05 x 10^7 x 0.720 ) / (9.109 x 10^-31 )

a = 3.86 x 10^81 m/s^2

c) Magnetic field acts perpendicular to the direction of velocity.

hence Force is in perpendicular direction so acceleration will also perpendicular.

so particle will move into circular path with constant speed.

(calaculated acceleration only change direction of velocity not magnitude )

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