Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The heating effect of electric current occurs when an electric current flows through a wire, causing the wire to become hot. This happens because the electrical energy is converted into heat energy.
A 'heating element' is a coil of wire found in appliances like electric heaters and geysers. These elements are often made of materials like Nichrome, which have high resistance to current flow.
The amount of heat produced in a wire depends on three main factors: the material of the wire, its length, and its thickness (cross-sectional area).
In an electric bulb, the filament (usually made of Tungsten) gets heated to such a high temperature that it begins to glow and emit light.
An Electric Fuse is a safety device based on the heating effect of current. It contains a wire with a low melting point that melts and breaks the circuit if the current exceeds a safe limit, preventing fires and damage.
Modern alternatives to fuses include Miniature Circuit Breakers (MCBs), which automatically switch off when current in a circuit exceeds the safe limit.
📐Formulae
💡Examples
Problem 1:
Why is Tungsten used as the filament in an electric bulb rather than Copper?
Solution:
Tungsten has a very high resistance and a very high melting point (approx ).
Explanation:
According to the heating effect, heat . Since Tungsten has high resistance, it produces enough heat to reach a temperature where it glows white-hot without melting. Copper has low resistance and a lower melting point, so it would melt before glowing.
Problem 2:
An electric heater is connected to a circuit. If the current flowing through the element is doubled, what happens to the heat produced, assuming resistance and time remain constant?
Solution:
The heat produced becomes four times the original amount.
Explanation:
Using the formula , we see that heat is proportional to the square of the current (). If current is doubled (), the new heat becomes , which is times the original heat.
Problem 3:
What is the primary function of a fuse wire in a household circuit?
Solution:
To act as a safety break in the circuit.
Explanation:
The fuse wire is made of an alloy with a low melting point. When the current increases excessively, the heat produced (calculated by ) melts the wire, breaking the circuit and preventing electrical fires.