# GCSE Physics revision guide

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• Created by: Max123
• Created on: 20-03-13 23:27

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Module P5 ­ Electric Circuits
Static electricity:
Build up of static electricity is cause by friction.
When you rub two insulating materials electrons move from one to the other, so one is
positive and one is negative (electrons are negative).
Electrically charged objects attract small objects.
ONLY ELECTRONS MOVE. If it loses electrons it becomes positive, if it gains them it becomes
negative.
Positive + Positive repel. Negative + Negative repel. Negative + Positive attract.
Dust is easily attracted to insulators (which easily gain a charge) and so things such as TV's
get dusty easily.
Electric Current:
Electric current is the flow of charge around a current.
It's measured in Amps.
Electrical charge flows along a conductor (the metal in the wires) because there are lots of
free electrons that are free to move around.
The battery pushes the charge all the way round the circuit. It's not used up and it doesn't
disappear.
Current depends on voltage and resistance.
Voltage is the driving force that pushes current around, its measures in Volts (V).
Resistance is anything slows down the flow of current in a circuit, ohms ().
Increase in voltage = more current
Increase in resistance = less current.
Like, if in a pipe line, the pump (battery) works harder, the water (current) travels round
faster. However, if you have something slowing the flow of water it slows down (resistance).
We normally say electrons flow from positive to negative, but the actually flow from
negative to positive. Opposite to `conventional current.'
Circuits ­ The basics:

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The standard circuit has an ammeter, a voltmeter in parallel with a component, and a
variable resistor. Oh, and a battery. Obv.
Voltmeters measure the potential difference between two points. So you have one
around the battery and one around the component so you can see how much energy
the component takes out compared to the amount of energy produced by the
battery.
Resistance:
The slope of a voltage current graph shows the
resistance.
The current through a resistor is proportional to the

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The current is constantly changing direction (alternating current).
Battery supply is DC (direct current).
AC is used for mains as it's easy to generate and is distributed more evenly.
Moving a magnet in a coil of wire induces current.
This is called electric induction.
The direction of the current depends on the way you move the magnet.
AC generators just turn the magnet and there's current.…read more

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So, if something needs more power, it takes more energy, so a light might only take 100W
(that's 100J every second) but a kettle might take 2.5kW (2500J per second).
Energy transferred (J) = Power (W) x Time (s)
Kilowatt-hours (kWh) are UNITS of energy.
Energy is usually measured in joules, but that's tiny. A kWh is the amount of electrical energy
converted by a 1 kW appliance left on for 1 hour.
Longer left on and high power rating means more cost.…read more

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When a wave hits a material all waves can be reflected, refracted (through material but
change direction) and diffracted (bends round making it spread out).
Reflection
o Angle of incidence = Angle of reflection
o When a wave hits a boundary between one medium and another, some is always
reflected.
Refraction ­ Waves change speed and direction.
o Waves travel at different speeds in
substances of different densities.
o EM waves normally travel slower in denser
mediums, sounds waves travel faster.…read more

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There are seven types of electromagnetic waves.
o Ronald McDonald Is Very Ugly X-men Glow
o Radio ­ Micro ­ Infra red ­ Visible Light ­ UV ­ X rays ­ Gamma rays
o As you go the frequency increases (so does energy)
o And as you go the wavelength increases.
o All waves travel at 300,000,000 (300million) m/s in a vacuum.
o Even different colours of light have the different wavelength.
Sounds waves can't travel through a vacuum.…read more

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FM waves have varying frequency.
o When there's a trough in the signal, the frequency is increased, or on a peak it is
increased. Or vice versa.
o They ignore the carrier part of the wave and extract the original signal. ^^^^^
Analogue and Digital Signals:
Analogue signals vary. Digitals either on or off.
o The amplitude or frequency of an analogue signal varies continuously; it could be any
value in a particular range.
o Digital signals are pulses.…read more