Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Heating Effect of Electric Current: When an electric current flows through a wire, the wire gets hot. This is known as the heating effect of current, governed by Joule's Law of Heating where heat is produced.
Electric Fuse: A safety device used in electrical circuits. It contains a wire made of a special alloy (like tin and lead) that has a low melting point. If the current exceeds a safe limit, the wire melts and breaks the circuit.
Causes of Excessive Current: Two main reasons for high current are 'Short Circuit' (when live and neutral wires touch directly) and 'Overloading' (connecting too many appliances to a single socket).
MCB (Miniature Circuit Breaker): These are switches that automatically turn off when current in a circuit exceeds the safe limit. They are preferred over fuses because they can be reset manually without needing replacement.
Magnetic Effect of Electric Current: Discovered by Hans Christian Oersted, this principle states that a current-carrying conductor produces a magnetic field around it.
Electromagnet: A coil of insulated wire wound around a soft iron core. It acts as a magnet only as long as the electric current flows through it. Its strength depends on the current and the number of turns in the coil.
Electric Bell: A device that works on the principle of the magnetic effect of current. It uses an electromagnet to pull an iron strip (armature) to strike a gong.
📐Formulae
💡Examples
Problem 1:
An electric heater is rated at and is connected to a supply. What should be the minimum rating of the fuse used for this heater?
Solution:
Current .
Explanation:
Since the heater draws approximately , a fuse with a rating slightly higher than this, such as a fuse, should be used to ensure safety without frequent blowing.
Problem 2:
Explain why a copper wire cannot be used as a fuse wire.
Solution:
Copper has a very high melting point and low resistance.
Explanation:
A fuse wire must melt easily when current is excessive. Because copper has a high melting point, it will not melt even if the current is dangerously high, failing to break the circuit and potentially causing a fire.
Problem 3:
How does the strength of an electromagnet change if the number of turns in the coil is doubled?
Solution:
The magnetic strength also doubles.
Explanation:
The magnetic field strength of an electromagnet is directly proportional to the number of turns in the coil. Mathematically, .