Question

4. Before television screens were all flat, they used to work by boiling off electrons ("cathode rays") from plates a hot filament and accelerating them towards a phosphor-coated screen. The acceleration was performed with a pair of charged parallel plates, as in a capacitor, with small holes to allow the beam to pass through. The beam was steered horizontally and vertically across the screen by varying the magnetic fields in deflecting coils. By varying these deflecting fields, the beam was scanned repeatedly across and down the screen, repainting the image on the phosphor many times per second accelerating Ay deflecting coils AX screen First let the accelerating voltage be AVa, the deflecting magnetic field be <0, 0, B>, the length of the deflecting coils be d, and the distance from the end of the deflecting coils to the screen be Ax By what distance 4), is the beam deflected vertically on the screen? Now suppose that V-36 kV. B 0.018 T, d-1.5 cm. and Ax 45 cm: how does Δ), work out numerically? (You will want to make the simplifying approximation that the x component of the electron's velocity does not change by very much as it goes through the deflecting coils.)

Answer 1

dl 2 1. 2 2.

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