The correct answer is Option 3: heating effect of current.

Explanation:

An electrical fuse works entirely on the principle of the heating effect of electric current (also known as Joule heating).

When an electric current ($I$) flows through a conductor with a specific resistance ($R$) for a given time ($t$), it generates thermal energy. This relationship is defined by the formula:

$$H = I^2Rt$$

How the fuse uses this: A fuse wire is designed with a relatively low melting point. Under normal operating conditions, the heat generated is low, and the wire remains intact.

When an overload occurs: If a short circuit or an electrical overload happens, the current ($I$) spikes drastically. Because the heat generated increases with the square of the current ($I^2$), the temperature of the fuse wire shoots up rapidly. The wire melts and breaks the circuit, safely cutting off the electricity before it can damage appliances or cause a fire.

Why the other options are incorrect:

Option 1 (Chemical effect): This involves chemical changes caused by passing electricity through a solution (e.g., electrolysis or electroplating), which plays no part in a fuse's function.

Option 2 (Magnetic effect): This is the generation of a magnetic field around a current-carrying wire (used in electromagnets, motors, or circuit breakers), but not standard thermal fuses.

Option 4 (Optical property): This refers to the emission of light due to electrical current (like in an LED or a lightbulb filament), which is not the operating mechanism of a fuse.