ICSE Class 10 Answered

When we take megnet near T.V SCREEN (which has cathode ray tube), the magnet distorts the picture as it distorts the path of electrons flowing from the electron gun towards the screen inside the tv. As electrons are negatively charged particles, their motion is distorted by a magnet.

Color CRT use three different phosphors which emit red, green, and blue light respectively. They are packed together in clusters called "triads" (as in shadow mask CRTs). A shadow mask tube uses a metal plate with tiny holes, placed so that the electron beam only illuminates the correct phosphors on the face of the tube.

If the shadow mask becomes magnetized due to a magnet brought near the TV screen, its magnetic field deflects the electron beams passing through it, causing color purity distortion as the beams bend through the mask holes and hit some phosphors of a color other than that which they are intended to strike; e.g. some electrons from the red beam may hit blue phosphors, giving pure red parts of the image a magenta tint. This results into a distorted picture or rainbow like picture appearing on that part of the screen.