P4 Revision Notes

Waves & Longitudinal Waves
Ultrasounds & Treatment
Uses of ultrasound
Background radiation
Uses of radiation
Nuclear Power

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  • Created on: 17-06-12 13:08
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A resistor is a component that reduces the current flowing in a circuit.
The higher the resistance, the harder it is for electricity to flow, so therefore the lower the
If you get an electric shock, it's the current that causes damage, not the voltage, so the higher the
resistance the less the damage.
Symbols used
V = Potential difference/current
I = Current
R = Resistance
t = Time
Variable Resistors
A variable resistor is a resistor that can be changed.
Old fashioned variable resistors are huge coils of wire with a slider on them.
Variable resistors are great for altering the current flowing through a circuit:
When you increase the resistance, the current decreases.
When you turn the resistance down, the current increases.
a, Measure the current (in amps) through the component.
b, Can be put anywhere in the series in a main circuit, but never in parallel like the voltmeter.
a, Measures the voltage (in volts) across the component.
b, Must be placed in parallel around the component under test ­ NOT around the variable resistor or
the battery!!!
C, The proper name for the voltage Is `potential difference'
Calculating Resistance: R= V/I
Resistance = potential difference / current
Waves & Longitudinal Waves
Sound is a longitudinal wave.
Features of a longitudinal wave:
o Sound waves squash up and stretch out the material they pass through making
compressions and rarefactions.
o The wavelength is a full cycle of the wave, e.g. from the crest to the crest.
o Frequency is the number of complete waves per second. It's measured in hertz. 50 Hz = 50
complete waves in 1 second.
o The amplitude tells you how much energy the wave is carrying or how loud the sound is. You
can see the amplitude of sound on a CRO (oscilloscope). CRO displays show sounds as

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You measure the amplitude from the
middle line to the crest (the top). NOT from the trough to the crest!
o Compressions are squashed together air particles in a wave.
o Rarefactions are spread out air particles in a wave.
Ultrasound is a longitudinal wave. This means that it travels as a pressure wave that is a series of
compressions and rarefactions.
Compressions and rarefactions make a person's eardrum vibrate and signals are sent out to the
brain.…read more

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Background Radiation
Background radiation comes from many sources.
The background radiation we receive comes from:
a, Radioactivity of naturally occurring unstable isotopes which are all around us ­ in the air, in food, in
building materials and in rocks.
b, Radiation from space, which are known as cosmic rays. These come mainly from the Sun.
c, Radiation due to human activity, e.g. fallout from nuclear explosions, or dumped nuclear waste. But
this proportion represents a tiny proportions of the total background radiation.…read more

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The advantage of irradiation over boiling is that it doesn't involve high temperatures so heat
sensitive things like thermometers and plastic instruments can be sterilised without damaging them.
Non-medical uses of radiation.
Tracers in industry.
Radioisotopes can be used to track the movement of waste materials, find he route of underground
pipe systems or detect leaks or blockages in pipes.…read more


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