(a) How does an electromagnet differ from a permanent magnet ?
(b) Name two devices in which electromagnets are used and two devices where permanent magnets are used.

Explanation

**Step-by-Step Solution:**

**(a)** **Differences between an Electromagnet and a Permanent Magnet:**

1. **Nature of Magnetism:**
- An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. When the current flows through the coil of wire wrapped around a core (usually made of soft iron), it generates a magnetic field.
- A permanent magnet, on the other hand, is a material that maintains a persistent magnetic field without the need for an external power source. It is made from materials like steel or certain alloys that have been magnetized.

2. **Strength of Magnetism:**
- The strength of an electromagnet can be varied by changing the amount of electric current flowing through it. This means that electromagnets can be turned on or off and their strength can be adjusted.
- The strength of a permanent magnet is fixed and does not change unless it is demagnetized or physically altered.

3. **Material Used:**
- Electromagnets typically use a soft iron core, which enhances the magnetic field when current flows through the wire.
- Permanent magnets are usually made from hard materials like steel, which retain their magnetism over time.

4. **Applications:**
- Electromagnets are used in applications where variable magnetic fields are required, such as in electric bells, motors, and magnetic cranes.
- Permanent magnets are used in applications where a constant magnetic field is needed, such as in refrigerator magnets and magnetic compasses.

**(b)** **Devices Using Electromagnets and Permanent Magnets:**

1. **Devices Using Electromagnets:**
- Electric bell: An electromagnet is used to strike a bell when the circuit is closed.
- Electric motor: Electromagnets are used to convert electrical energy into mechanical energy.

2. **Devices Using Permanent Magnets:**
- Refrigerator magnet: Used to hold notes and reminders on the refrigerator door.
- Magnetic compass: Utilizes a permanent magnet to indicate the direction of the Earth's magnetic field.

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