An iron nail wrapped in wire, connected to a battery, picks up paper clips like a magnet — and drops them the instant the circuit opens. No magnet involved. How?
Key idea
The Magnetic Effect of Electric Current
Place a compass under a wire, then switch the circuit ON
the needle deflects. Switch OFF, and it returns to normal.
Hans Christian Oersted, 1820
Discovered this link between electricity and magnetism quite by accident, during a lecture demonstration.
Key idea
Electromagnets
Wind wire into a coil, connect it to a cell, and the coil behaves like a magnet — an electromagnet.
An iron core makes it strongerSlide an iron nail inside the coil, and the electromagnet becomes far stronger — the basis of nearly every practical electromagnet.
Key idea
Controlling an Electromagnet
1
Two poles, like any magnet
An electromagnet has North and South poles, found by testing which end attracts a compass pole.
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2
What changes its strength
More current (more cells) or more coil turns makes it stronger. Reversing the current's direction reverses its poles.
Key idea
Lifting Electromagnets and Earth's Magnetism
1
Lifting electromagnets
Powerful electromagnets hung from cranes — switch current ON to lift iron or steel, OFF to drop it. Common in factories and scrap yards.
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2
Earth, a giant magnet
Currents from moving liquid iron in Earth's core create its magnetic field — helping migratory animals navigate, and shielding us from harmful space particles.
Key idea
The Heating Effect of Electric Current
A conductor resists the flow of current
and that resistance converts some electrical energy into heat.
Not all wires heat the same
A nichrome wire heats up more than a copper wire of the same size, because it offers higher resistance.
Key idea
What Decides How Much Heat Is Generated
1
Current
More current, more heat.
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2
Material
Higher resistance, more heat.
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3
Thickness & length
Thinner, longer wires heat more.
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4
Time
Longer current flow, more total heat.
Key idea
Appliances That Use This Effect
1
Everyday appliances
Room heaters, stoves, kettles, irons, immersion rods, and hair dryers all contain a heating element — a rod or coil that heats up when current flows.
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2
Safety and industry
Overheating can melt plugs or start fires — household circuits include safety devices. Industrially, electric furnaces reach very high temperatures to melt and recycle scrap steel.
Key idea
The Voltaic Cell
Two different metal electrodes, dipped in an electrolyte, react chemically to produce electric current.
Even a lemon can power an LEDA copper wire, an iron nail, and lemon juice as the electrolyte can light an LED — the same principle behind every battery, named after Volta and Galvani.
Key idea
Dry Cells
Paste, not liquid. A zinc container (negative terminal) and a central carbon rod (positive terminal), with a paste-like electrolyte — single-use, and must be disposed of once used up.
Key idea
Rechargeable Batteries
Lithium-ion, today's standardUsed in phones, laptops, cameras, inverters, and electric vehicles — recharged and reused many times, though they eventually wear out too.
Handle with careUsed batteries contain valuable and harmful materials — they belong in e-waste recycling, never regular garbage.
Chapter · Key terms to remember
Key Terms
Magnetic effect of current
A current-carrying wire creates a magnetic field.
Electromagnet
A current-carrying coil that behaves like a magnet.
Heating effect of current
Heat generated in a conductor due to resistance.
Chapter · Key terms to remember
More Key Terms
Resistance
Opposition a conductor offers to current flow.
Electrolyte / Electrode
The conducting liquid / the metal rod in a cell.
Voltaic (Galvanic) cell
Generates current via a chemical reaction.
Chapter · Key terms to remember
More Key Terms
Dry cell
A single-use cell with a paste electrolyte.
Rechargeable battery
Can be recharged and reused many times.
Questions for your notebook
Write these down, then discuss
1
Fill in the blanks: (i) The solution used in a Voltaic cell is called ___. (ii) A current-carrying coil behaves like a ___.
2
True or False: (i) Dry cells are less portable than Voltaic cells. (ii) A coil becomes an electromagnet only when current flows through it. (iii) A single-cell electromagnet attracts more paper clips than the same electromagnet with 2 cells.
3
Current flows through a nichrome wire briefly. (i) The wire becomes warm. (ii) A compass below it deflects. Which is correct?
Project as-is — students copy the questions, then the class discusses answers together.