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Electricity: Magnetic and Heating Effects - Does a Current Carrying Wire Get Hot?

Grade 8CBSE

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

🔑Concepts

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The Heating Effect of Electric Current: When an electric current flows through a wire, the wire gets hot. This is known as the heating effect of electric current. This effect is utilized in appliances like electric heaters, irons, and geysers.

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The amount of heat produced in a wire depends on its material, length, and thickness (cross-sectional area). For a given current, a wire with higher resistance (RR) produces more heat.

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An 'Element' is a coil of wire used in heating appliances. When current passes through the element, it becomes red hot and gives out heat. These are usually made of materials like Nichrome which have a high melting point and high resistance.

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Electric Fuse: This is a safety device based on the heating effect of current. It contains a wire made of a special alloy that melts quickly and breaks the circuit if the current exceeds a safe limit, preventing fires and damage to appliances.

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Magnetic Effect of Electric Current: When electric current flows through a wire, it behaves like a magnet. This was first observed by Hans Christian Oersted, who noticed a compass needle deflects when placed near a current-carrying wire.

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Electromagnet: A coil of insulated wire wrapped around a piece of magnetic material (like soft iron) acts as a magnet when current passes through it. The magnetism lasts only as long as the current flows.

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The strength of an electromagnet can be increased by increasing the number of turns in the coil or by increasing the current (II) flowing through the circuit.

📐Formulae

H=I2×R×tH = I^2 \times R \times t

P=V×IP = V \times I

V=I×RV = I \times R

💡Examples

Problem 1:

An electric heater is connected to a power supply. If the resistance of the heating element is 50Ω50 \Omega and a current of 2A2 A flows through it for 1010 seconds, calculate the heat produced.

Solution:

Given: Current (II) = 2A2 A, Resistance (RR) = 50Ω50 \Omega, Time (tt) = 10s10 s. Using the formula for heat produced: H=I2RtH = I^2 R t H=(2)2×50×10H = (2)^2 \times 50 \times 10 H=4×50×10H = 4 \times 50 \times 10 H=2000JH = 2000 J

Explanation:

The heat produced is calculated using Joule's Law of Heating, where heat is directly proportional to the square of the current, the resistance, and the time for which current flows.

Problem 2:

A circuit has two appliances drawing currents of 5A5 A and 8A8 A respectively. If they are connected in parallel, calculate the total current to check if a 10A10 A fuse will blow.

Solution:

To find the total current, we add the individual currents: 5+813\begin{array}{r} 5 \\ + 8 \\ \hline 13 \end{array} Total current Itotal=13AI_{total} = 13 A.

Explanation:

Since the total current (13A13 A) is greater than the fuse limit (10A10 A), the fuse wire will melt due to the heating effect of the excess current, breaking the circuit.

Problem 3:

Why is a compass needle deflected when brought near a wire carrying current?

Solution:

The deflection occurs because of the magnetic effect of electric current. The current-carrying wire creates a magnetic field around it, which exerts a force on the magnetic needle of the compass.

Explanation:

This demonstrates that electricity and magnetism are linked, a principle used in making electromagnets and electric bells.

Does a Current Carrying Wire Get Hot? Class 8 Notes & Examples