Magnetic Effect of Electric Current

Oersted’s Discovery

In 1820, a Danish scientist named Hans Christian Oersted noticed something strange. When he switched on an electric circuit, a compass needle lying nearby moved!

• Observation: A compass needle deflects when placed near a current-carrying wire.
• Conclusion: Electric current produces a magnetic field around it.

Electromagnets

We can use this effect to create temporary magnets called electromagnets.

How to make one?

1. Take a magnetic material (like an iron nail).
2. Wind an insulated copper wire tightly around it in a coil.
3. Connect the wire ends to a battery.

When current flows, the nail behaves like a strong magnet and can attract paper clips. When the current stops, it loses its magnetism.

Polarity of an Electromagnet

An electromagnet has a North Pole and a South Pole, just like a bar magnet.

• If the compass North pole is attracted to End A, then End A is the South Pole (unlike poles attract).
• If you reverse the direction of current (swap battery terminals), the poles of the electromagnet also reverse.

Factors Affecting Strength

The strength of an electromagnet depends on:

1. Current Strength: More cells (batteries) $\rightarrow$ Stronger magnet.
2. Number of Turns: More turns in the coil $\rightarrow$ Stronger magnet.
3. Core Material: Using soft iron as a core makes it much stronger than air or wood.