Physics: Electricity and Magnetism: UPSC Previous Year Questions (Science and Technology)

Explanation

A fuse is a safety device designed to protect electrical circuits from overloads or short circuits. It works by having a thin wire or filament that melts when the current exceeds a certain level, breaking the circuit and preventing damage to electrical appliances. The fuse is specifically made with a low melting point to ensure it melts quickly in the event of excessive current flow, protecting the circuit from potential damage. Options (a), (b) and (d) are incorrect:

They are wired in series with the circuit not parallelbecause this setup ensures that the full current passing through the circuit flows through the fuse. This allows the fuse to effectively interrupt the circuit and halt the electrical flow in the event of an overcurrent. Fuses are not constructed from silver alloys as they are usually made from materials such as copper, zinc, or tin. They do not need high resistance rather, they should allow normal current flow until the current exceeds a safe limit. Direction: The following item consists of two statements, one labeled as the Assertion (A) and the other as Reason (R). You have to answer this item using the code given below.

Explanation

Assertion (A) is true: The flow of electric current through a conductor causes energy dissipation in the form of heat due to the collisions between free electrons and the metal atoms. Reason (R) is true: As electrons travel through a metal as they collide with metal atoms causing the atoms to vibrate more and collide with each other which produces heat. The phenomenon is known as Joule heating. When current flows through the metal wire, the free electrons that carry the current interact with the metal atoms, transferring energy and causing the atoms to vibrate more, leading to a temperature increase due to Joule heating. The amount of heat generated depends on factors such as the wire’s resistance, the current, and the duration of the current flow. This effect is the foundation for devices like electric heaters. Thus Reason (R) explains Assertion (A)