Question

Explain why a blackened platinum strip when placed at the radius of curvature turns red hot, only when the cathode taken has a concave shape.

Answer 1

1. When a blackened platinum strip kept at the radius of curvature is exposed to high-intensity radiation, the electrons on the metal's surface are excited, while the energy of underlying electrons is increased.
2. Reason: The following variables cause the strip to get red hot:

(a) Electrons travelling from a concave cathode almost always move in a straight line for a reasonable distance.

(b) The maximal rays of electron-rich high-energy radiation impinge on the object kept on the radius of curvature of the concave cathode because the radius of curvature is close enough.

3. Thus, when a strip of platinum is placed on the radius of curvature of a concave cathode, it becomes red hot.