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Electricity: Magnetic and Heating Effects - Does an Electric Current Have a Magnetic Effect?

Grade 8CBSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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When an electric current flows through a wire, it produces a magnetic field around it. This is called the magnetic effect of electric current.

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A compass needle, which is a tiny magnet, gets deflected when placed near a wire carrying electric current because of this magnetic field.

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Hans Christian Oersted was the first scientist to observe that a current-carrying wire behaves like a magnet.

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An electromagnet consists of a coil of insulated wire wrapped around a soft iron core. It loses its magnetism when the current is switched off.

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The strength of an electromagnet depends on the amount of current II passing through it and the number of turns nn in the coil.

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The Heating Effect of current occurs when electric energy is converted into heat energy as current flows through a conductor with resistance RR.

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The Electric Bell is a common application of the magnetic effect of current, where an electromagnet is used to vibrate a hammer against a gong.

📐Formulae

H=I2RtH = I^2 R t

P=V×IP = V \times I

V=I×RV = I \times R

💡Examples

Problem 1:

Why does a compass needle show deflection when brought near a current-carrying wire?

Solution:

The deflection occurs because the electric current flowing through the wire creates a magnetic field around it. Since the compass needle is itself a small magnet, it interacts with the magnetic field of the wire, resulting in a force that causes it to deflect.

Explanation:

This demonstrates the magnetic effect of electric current discovered by Hans Christian Oersted.

Problem 2:

If the resistance RR of a wire is 10 Ω10 \, \Omega and a current II of 2 A2 \, A flows through it for 5 s5 \, s, calculate the heat produced HH.

Solution:

Using the formula H=I2RtH = I^2 R t, we substitute the given values: H=(2)2×10×5H = (2)^2 \times 10 \times 5 H=4×10×5H = 4 \times 10 \times 5 H=200 JH = 200 \, J

Explanation:

The heat produced is directly proportional to the square of the current, the resistance, and the time for which the current flows.

Problem 3:

A student wants to increase the strength of an electromagnet. Suggest two ways to do this.

Solution:

  1. Increase the amount of current II flowing through the coil.
  2. Increase the number of turns nn in the coil of wire.

Explanation:

The magnetic field strength of a solenoid/electromagnet is directly proportional to both the current and the density of the turns.