Electricity is the flow of electric charge, and magnetism is the property of magnets to attract iron. The two are linked together as electromagnetism. These basics are used in motors, generators and daily appliances, and are common in science papers.
Electric Current and Ohm's Law
- Electric current is the flow of charge; its SI unit is the ampere (A).
- Ohm's Law: V = IR (Voltage = Current x Resistance).
- Potential difference (voltage) is measured in volt (V).
- Resistance is measured in ohm.
Conductors and Insulators
- Conductors like copper and silver allow current to pass.
- Insulators like rubber and plastic do not allow current.
- Household wiring uses copper for conduction and plastic for insulation.
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Magnetism
- A magnet has two poles: north and south.
- Like poles repel; unlike poles attract.
- A freely hanging magnet always points north-south.
- Magnetic field lines run from north to south outside the magnet.
Electromagnetism
- Oersted showed that current produces a magnetic field.
- Faraday discovered electromagnetic induction, the base of generators.
- An electric motor converts electrical energy to mechanical energy.
- A generator converts mechanical energy to electrical energy.
Quick Revision Points
- SI unit of current is ampere.
- Ohm's Law: V = IR.
- Resistance unit is ohm; voltage unit is volt.
- Copper is a good conductor; rubber is an insulator.
- Like magnetic poles repel, unlike attract.
- Faraday discovered electromagnetic induction.
- Motor: electrical to mechanical; generator: mechanical to electrical.