When electric current flows in a purely resistive circuit electrical energy gets fully converted into heat energy. The amount of heat produced (H) in the circuit is found to be directly proportional to (i) the square of current (I²) (ii) the resistance (R) of the conductor and (iii) the time (t) for which current flows. In other words H = I²Rt. Electrical devices such an electric fuse, electric heater, electric iron etc. are all based on this effect called heating effect of electric current.
Read the source and answer the sub-parts that follow.
Generated by claude-sonnet-4-6 · 2026-06-15 06:46 · grounding stimulus
Model Answer
(a) Properties of heating elements:
- High resistivity
- High melting point
(b) Properties of electric fuse wire:
- Low melting point
- High resistivity
(c) Principle: An electric fuse works on the heating effect of electric current (Joule's heating effect).
Working: A fuse wire has low melting point and high resistivity. When an accidentally high current flows through the circuit, excessive heat is produced in the fuse wire (H = I²Rt). This heat melts the fuse wire, breaking the circuit. As the circuit breaks, current stops flowing, and the electrical appliances are saved from damage due to overloading.
Source: Chapter 12 – Electricity, Heating Effect of Electric Current
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Explanation
- (a) Heating elements (like in iron/heater) need high resistivity to produce enough heat and high melting point to withstand the heat without melting.
- (b) Fuse wire must melt easily (low melting point) when excess current flows, so it needs opposite properties to heating elements — this contrast is a favourite examiner trap.
- (c) Always name the principle first, then explain the mechanism in sequence: high current → heat produced → fuse melts → circuit breaks → appliances saved. Mentioning H = I²Rt earns credit.