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. This means a wire behaves like a magnet when an electric current flows through it.
An Electromagnet is the heart of the bell. It consists of a coil of insulated copper wire wound around a soft iron core. When current passes through the coil, the core becomes magnetized.
The Armature is a soft iron strip mounted on a spring. It is positioned in front of the poles of the electromagnet.
Make and Break Mechanism: When the circuit is closed, the electromagnet attracts the armature. As the armature moves towards the electromagnet, the hammer strikes the gong. Simultaneously, the contact at the Contact Screw is broken.
Once the circuit is broken, the current drops to , the electromagnet loses its magnetism, and the spring pulls the armature back to its original position, making the contact again.
The Heating Effect of Current () is often a side effect in the coils of the bell, governed by the resistance and the time for which current flows.
📐Formulae
💡Examples
Problem 1:
What would happen to the functioning of an electric bell if the soft iron core was replaced by a steel core?
Solution:
The bell would stop ringing after the first strike.
Explanation:
Unlike soft iron, steel becomes a permanent magnet when current flows through the coil. Even when the circuit is broken at the contact screw, the steel core would retain its magnetism and continue to hold the armature, preventing it from returning to complete the circuit again.
Problem 2:
Identify the part of the electric bell that is responsible for breaking the circuit automatically.
Solution:
The Contact Screw and the Armature strip.
Explanation:
When the electromagnet attracts the armature, the iron strip moves away from the contact screw. This creates an air gap, breaking the electrical path and causing .
Problem 3:
If the number of turns in the coil of the electromagnet is doubled, how does it affect the bell?
Solution:
The magnetic field strength increases, making the bell ring louder or more forcefully.
Explanation:
The magnetic field is directly proportional to the number of turns (). More turns create a stronger magnetic pull on the armature.