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Electricity & Magnetism
What you should know.
- + charges repel each
other. - charges repel each other. A + charge attracts a - charge.
- An uncharged (neutral)
object has got an equal number of electrons (-) and protons (+).
- Things can be 'charged'
by rubbing them. It is the - charges (electrons) that move.
- An electric current is a
flow of electrons. It is measured in amperes (A), by an ammeter. An ammeter
must be connected in series in a circuit.
- In a parallel circuit
there is more than one path. Some electrons go along one path, and the rest
go along the other path.
- Electrons carry energy
with them. The higher the voltage of the battery, the more energy the
electrons have.
- A good conductor has a
low resistance. An insulator has a high resistance.
- The end of a compass that
points North is the N-pole of the magnet. Two N-poles (or 2 S-poles) repel
each other. A N-pole attracts a S-pole.
- An electric current makes
a magnetic field. Reversing the current makes the field point the opposite
way, as shown by a compass.
- A coil carrying a current
has a magnetic filed like a bar-magnet. It is an electro-magnet.
- The strength of an
electro-magnet depends on the current in the coil, the number of turns on
the coil and whether there is an iron core.
- How an electric bell
works.
- How a relay works.
- How a circuit-breaker
works.
What you should be able to do.
- Explain what is happening
when a plastic ruler is rubbed and becomes positive.
- Read the scale on an
ammeter correctly.
- Connect an ammeter into a
circuit correctly.
- Use a variable resistor
to change the brightness of a bulb.
- Draw a circuit diagram
using the correct symbols.
- Connect a circuit with 2
bulbs in parallel.
- Measure the current at
different positions in a parallel circuit.
- Connect a voltmeter
across a circuit correctly.
- Read the scale on a
voltmeter correctly.
- Analyse a circuit, to
decide which switches are needed to light a bulb.
- Plot a magnetic filed,
using iron filings, round:
- a bar magnet
- an electro-magnet
- Investigate to find out
what affects the strength of an electro-magnet.
- Explain how
electro-magnetic gadgets work, for example, an electric bell, a relay, a
circuit-breaker.
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