Cathode ray tube deflection analysis · CAP 2005 #24
Physics · electromagnetism
Problem
A horizontal cathode ray tube (CRT) is set so that its electron beam produces a spot of light at the centre of the screen when no external electromagnetic field is present. When you look straight at the screen, however, you discover that the spot, instead of being at the centre as it should, is shifted a bit to the right. Suspecting what the cause of this deflection may be, you rotate the CRT by 180° around its vertical axis. Facing the screen, you find that the spot of light is still shifted to right of centre by the same distance as before. You conclude that the CRT is immersed in
(a) an electric field directed horizontally to the left with respect to the screen's initial position;
(b) an electric field directed horizontally to the right with respect to the screen's initial position;
(c) a magnetic field directed vertically upward with respect to the screen's initial position;
(d) a magnetic field directed vertically downward with respect to the screen's initial position;