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8.1 FROM THE UNIVERSE TO THE ATOM

THE ATOM

P81 008

The electric deflecting plates in a cathode ray tube are 12.0 mm apart and a potential difference of 1234 V across them. A beam of positively charged particles moving at 2.67´10⁴ m.s^-1 travels through the plates undeflected.

(a) Sketch the experimental setup.

(b) Calculate the electric field between the plates.

(c) Calculate the magnetic field strength.

View solution below only after you have completed the answering the question.

Solution

Electric field E = V / d = 1.03´10⁵ V.m^-1

For beam of positive charges to move un-deflected, magnitudes of the electric and magnetic forces must be equal.

F_E = F_B

q E = q v B

B = E / v = 3.85 T