Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
The electric bell works on the principle of the Magnetic Effect of Electric Current. When current passes through a coil, it behaves like a magnet.
An electromagnet is a core of magnetic material (usually soft iron) surrounded by a coil of insulated copper wire. Its magnetism lasts only as long as the current flows ().
The core of the electromagnet is made of Soft Iron because it is a temporary magnet. It magnetizes and demagnetizes quickly, allowing the bell to ring continuously.
The Contact Screw and the Armature form a 'make and break' circuit. When the armature is attracted to the electromagnet, the contact at the screw is broken, stopping the flow of current.
The Gong and Hammer mechanism: The hammer is attached to the armature. When the armature is pulled toward the electromagnet, the hammer strikes the gong to produce sound.
Sequence of operation: Circuit closes Electromagnet gets magnetized Armature is attracted Hammer hits gong Circuit breaks at screw Magnetism lost Spring pulls armature back Circuit closes again.
📐Formulae
💡Examples
Problem 1:
Why is steel not used as the core of the electromagnet in an electric bell instead of soft iron?
Solution:
Steel is a hard magnetic material and retains its magnetism even after the current is switched off.
Explanation:
If steel were used, the electromagnet would become a permanent magnet. After the first strike, the armature would remain stuck to the core, the circuit would stay broken, and the bell would not ring continuously.
Problem 2:
What happens to the ringing frequency of the bell if the voltage of the battery is increased?
Solution:
The bell will ring more rapidly and loudly.
Explanation:
According to , increasing the voltage increases the current . Since the magnetic field strength , the electromagnet becomes stronger, pulling the armature with more force and speed, resulting in faster strikes.
Problem 3:
Name the part of the electric bell that helps in bringing the armature back to its original position once the circuit is broken.
Solution:
The Spring or the Springy metal strip.
Explanation:
When the electromagnet loses its magnetism (demagnetizes), it no longer attracts the soft iron armature. The elastic potential energy stored in the spring pulls the armature back to touch the contact screw, completing the circuit again.