Final answer:
When a negative magnet is placed over a cathode-ray tube, the negatively charged electron beam is deflected in a direction opposite to that of the negative magnetic field.
Step-by-step explanation:
When a negative magnet is applied to a cathode-ray tube (CRT), the electron beam inside the CRT is affected by the magnetic field. Electrons emitted from the cathode are accelerated toward the anode, producing a visible glow when they excite atoms and molecules in the gas inside the tube.
Magnetic fields cause the electron beam to bend in a direction that is determined by the charge of the electrons and the orientation of the magnetic field. J. J. Thomson, a notable English physicist, conducted experiments that proved that cathode rays were deflected by the magnetic field due to their negative charge.
This deflection is towards the direction opposite of the source of the negative magnetic field, indicating the negative charge of the electron beam.