Chapter 20, Problem 13Q

To determine

Why a strong magnet held near a CRT television screen causes the picture to become distorted? And also, to explain why the picture sometimes goes completely black where the field is the strongest.

Answer to Problem 13Q

Solution:

A charge particle in a magnetic field experiences a magnetic force, hence a strong magnetic field can distort a picture and even sometimes darkness on the screens of television.

Explanation of Solution

In CRT (cathode ray tube)television, picture is formed on the screen due to the momentary interaction of the electron at screen. On bringing a strong magnet near a screen, the electrons reaching the screen are subjected to a strong magnetic field. But a charge particle in a magnetic field experiences a magnetic force. Due to this the electrons reaching the screen experiences a force, gets deflected and reaches a wrong place on the screen. Hence picture gets distorted.

If the magnetic field is too strong, then due to bending the electrons may not reach the screen hence causes darkness.

Conclusion:

A charge particle in a magnetic field experiences a magnetic force, hence a strong magnetic field can distort a picture and even sometimes darkness on the screens of television.