The picture tube in a television uses magnetic deflection coils rather than elec

Question

The picture tube in a television uses magnetic deflection coils rather than electric deflection plates. Suppose an electron beam is accelerated through a 55.0 -kV potential difference and then through a region of uniform magnetic field 1.00 cm wide. The screen is located 10.0 cm from the center of the coils and is 80.0 cm wide. When the field is turned off, the electron beam hits the center of the screen. What field magnitude is necessary to deflect the beam to the side of the screen? Ignore relativistic corrections.

_____ mT

Explanation / Answer

mass of electron m =9.1*10^-31 kg

charge of electron q =1.6*10^-19 C

V =55 kV, R = 1cm

From conservation of energy

(1/2)mv^2 = qV

0.5*9.1*10^-31 *v^2 =1.6*10^-19*55*1000

v =1.39*10^8 m/s

From newton second law

qvB = mv^2/R

qB = mV/R

B = mv/Rq

B = (9.1*10^-31*1.39*10^8)/(0.01*1.6*10^-19)

B =79 mT

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