Final answer:
When the concave reflecting surface of a torch gets rusted, it affects the beam of light by scattering it in different directions, decreasing its intensity and focus. A smooth reflecting surface maintains the parallel nature of light rays for a more concentrated and powerful beam.
Step-by-step explanation:
When the concave reflecting surface of a torch gets rusted, it can affect the beam of light from the torch in several ways. Firstly, the rusted surface becomes rough and diffuses the light, causing the beam to scatter in many different directions. This leads to a decrease in the intensity and focus of the beam. Additionally, the rust can also cause the surface to become uneven, resulting in the reflection of light in various angles, further reducing the coherence and directionality of the beam.
In contrast, a smooth and polished reflecting surface, such as a mirror or a lens, can maintain the parallel nature of the incident light rays. This is important for creating a focused and directed beam of light. For example, a converging lens can take parallel rays of light and bring them to a single focal point, resulting in a more concentrated and powerful beam. However, when the reflecting surface of a torch is rusted and no longer smooth, the beam of light will not become parallel, and its intensity, focus, and directionality will be compromised.