Chapter 4 Notes: Electricity: Magnetic and Heating Effects

Magnetic Effect of Electric Current

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

• When the current is ON → compass needle deflects (moves)
• When the current is OFF → compass needle returns to original position
• This was first discovered by scientist Hans Christian Oersted in 1820

Key Cause-Effect:

Electric current flowing → Magnetic field created → Compass needle deflects

Electromagnets

A current-carrying coil that behaves like a magnet is called an electromagnet. It has two poles — North and South — just like a bar magnet.

How to make one:

• Wind insulated wire around an iron nail to form a coil
• Connect the coil to a battery → nail becomes a magnet
• Disconnect the battery → nail loses magnetism

How to make an electromagnet STRONGER:

Factor	Effect
More cells (more current)	Stronger magnet
More turns of wire	Stronger magnet
Iron core inside coil	Stronger magnet

Changing direction of current → poles of electromagnet get reversed!

Real-life use: Lifting Electromagnets

Crane electromagnets can lift heavy iron/steel objects when current is ON and release them when current is OFF.

Heating Effect of Electric Current

When electric current passes through a conductor, the conductor gets heated. This is called the heating effect of electric current.

Why does it happen?

• Every conductor opposes (resists) the flow of current — this is called resistance
• This resistance causes electrical energy to convert into heat energy
• Nichrome wire has higher resistance than copper → heats up more

What affects the amount of heat produced?

• More current → More heat
• Higher resistance of wire → More heat
• Longer duration of current flow → More heat

Common Household Appliances using Heating Effect:

• Electric heater, electric iron, electric kettle
• Hair dryer, electric stove, immersion rod
• All these contain a heating element (a coil/rod of wire like nichrome)

How Batteries Generate Electricity

A cell or battery generates electric current through chemical reactions inside it.

Types of Cells:

1. Voltaic Cell (Galvanic Cell)

• Has two metal rods (electrodes) made of different materials
• Dipped in a liquid called electrolyte (weak acid or salt solution)
• Chemical reaction between electrodes and electrolyte produces electricity
• When chemicals are used up → cell becomes 'dead'
• Cannot be recharged
• Example: Lemon cell (copper wire + iron nail + lemon juice)

2. Dry Cell

• Zinc container = negative terminal
• Carbon rod with metal cap = positive terminal
• Paste-like electrolyte (not liquid) surrounds the carbon rod
• Single-use: once used up, must be disposed of

3. Rechargeable Batteries

• Can be charged and reused multiple times
• Used in: phones, laptops, cameras, inverters, electric vehicles
• Most common type: Lithium-ion (Li-ion) battery
• After many charge cycles, they slowly wear out