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What is an electromagnet, and how can we make one?

Class 8 ScienceNCERT chapter: Electricity: Magnetic and Heating Effectsइसे हिंदी में पढ़ें

Exam-ready answer

An electromagnet is a temporary magnet made by passing electric current through a coil of insulated wire wound around a piece of soft iron. It behaves like a magnet only as long as the current flows. To make one, wind insulated copper wire around an iron nail and connect its ends to a cell through a switch.

Explanation

When an electric current flows through a wire, it produces a magnetic effect around the wire. A compass needle placed near a current-carrying wire turns away from its usual direction, and returns when the current stops. Winding the wire into a coil concentrates this magnetic effect, and placing a piece of iron inside the coil makes it much stronger.

To make an electromagnet, take a long iron nail and about a metre of insulated copper wire. Wind the wire tightly around the nail in many turns, all in the same direction. Remove the insulation from the two free ends and connect them to a cell through a switch. When the switch is on, the nail attracts paper pins; when it is off, the pins fall.

The strength of an electromagnet increases when the number of turns in the coil is increased or when the current is increased, for example by using more cells. Electromagnets can be switched on and off, so they are used in cranes to lift scrap iron, in electric bells, in loudspeakers and motors, and by doctors to remove iron pieces from the eye.

Points to remember

  1. Electromagnet: a coil of insulated wire wound on a soft iron core that becomes a magnet when current flows.
  2. It is a temporary magnet; it loses its magnetism when the current is switched off.
  3. Its strength increases with more turns of wire and more current.
  4. An electric current produces a magnetic effect, which deflects a nearby compass needle.
  5. Uses: cranes for lifting scrap iron, electric bells, loudspeakers, motors and removing iron pieces from the eye.

Exam tip

Draw a labelled diagram of the nail, coil, cell and switch, and mention the two ways to make the electromagnet stronger: more turns and more current.

Questions students also ask

How is an electromagnet different from a permanent magnet?
An electromagnet works only while current flows and can be switched on or off; its strength can be changed. A permanent magnet keeps its magnetism all the time and its strength cannot be easily changed.
Why is insulated wire used to make an electromagnet?
The turns of the coil touch each other. If the wire were bare, current would jump between the turns instead of going around the core, and the coil would not produce a strong magnetic effect. Insulation forces the current to follow the whole coil.
How does an electric bell use an electromagnet?
When the switch is pressed, the electromagnet pulls an iron strip with a hammer, which strikes the gong. This breaks the circuit, the magnet stops working and the strip springs back, completing the circuit again. The repeated cycle makes the bell ring.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.