AQA Physics P2 revision

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  • Created on: 21-04-11 09:17
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Physics 2 Revision
Particle Relative Mass Relative Charge
Proton 1 +1
Neutron 1 0
Electron Very small -1
An atom has no overall electrical charge because there are equal amounts of
protons and electrons. However, they have equal but opposite charge.
Isotopes are atoms that have the same number of protons, but different
numbers of neutrons.
The nuclei of some isotopes are unstable. They emit radiation and break
down to form smaller nuclei.
An early model of the atom was the plum pudding model. It was disproved
by Rutherford's scattering experiment and replaced by the nuclear model.
The number of protons in the nucleus of an atom is called its atomic number:
the atoms of a particular element all have the same number of protons
the atoms of different elements have different numbers of protons
This is the full chemical symbol for chlorine-35.
The proton number is shown below the chemical symbol,
and the mass number is shown above. In the example below, the
atomic number is 17 and the mass number is 35. This means that
each of these atoms has:
17 protons
17 electrons
35 - 17 = 18 neutrons
Isotopes are the atoms of an element with different numbers of neutrons.
They have the same proton number, but different mass numbers.
Radioactive decay
The nuclei of some isotopes are unstable.
They can split up or `decay' and release radiation. Such isotopes are called
radioactive isotopes or radioisotopes.

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Page 2

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When a radioactive isotope decays, it forms a different atom with a
different number of protons.
Changing elements
When an atom emits alpha or beta radiation, its nucleus changes. It becomes
the nucleus of a different element. This is because the number of protons in
the nucleus determines which element the atom belongs to.…read more

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Isotopes are atoms with the same atomic number but different mass
Most of the mass of an atom found in the nucleus.
In the plum pudding model of the atom, the plums were electrons
The type of radiation used in Rutherford's scattering experiment was alpha
Attraction and repulsion
Moving charges
When you rub two different insulating materials against each other they
become electrically charged. This only works for insulated objects -
conductors lose the charge to earth.…read more

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Many power stations burn fossil fuels such as coal and oil. Smoke is
produced when these fuels burn.
Smoke comprises tiny solid particles, such as unreacted carbon, which can
damage buildings and cause breathing difficulties.
To avoid this, the smoke is removed from waste gases before they pass out
of the chimneys.
The electrostatic precipitator is the device used for this job.
1. Smoke
particles pick up a negative charge.
2. Smoke particles are attracted to the collecting plates.
3.…read more

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To check for a complete circuit, follow a wire coming out of the battery
with your finger. You should be able to go out of the battery, through the
lamp and back to the battery.
To check for a short circuit, see if you can find a way past the lamp
without going through any other component. If you can, there is a short
circuit and the lamp will not light.…read more

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No current can flow if the circuit is broken, for example, when a switch is
open.…read more

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When two or more components are connected in series, the same current
flows through each component.
When two or more components are connected in parallel, the total current
flowing through the circuit is shared between the components.
Resistance and resistors
An electric current flows when electrons move through a conductor. The
moving electrons can collide with the atoms of the conductor. This makes it
more difficult for the current to flow, and causes resistance.…read more

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A graph of current - vertical axis - against potential difference -
horizontal axis - shows you how the current flowing through a component
varies with the potential difference across it.
Resistor at constant temperature
The current flowing through a resistor at a constant temperature is
directly proportional to the potential difference across it.
A component that gives a graph like the one to the
right is said to follow Ohm's Law.
The filament lamp
The filament lamp is a common type of light bulb.…read more

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Thermistors are used as temperature sensors - for example, in fire alarms.
Their resistance decreases as the temperature increases:
1. At low temperatures, the resistance of a thermistor is high and
little current can flow through them.
2. At high temperatures, the resistance of a thermistor is low and
more current can flow through them.
LDRs (light-dependent resistors) are used to detect light levels, for
example, in automatic security lights.
Their resistance decreases as the light intensity increases:
1.…read more

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Where does each wire go?
There is an easy way to remember
where to connect each wire.
Take the second letters of the words
blue, brown and striped.
This reminds you that when you look
into a plug from above:
blue goes left, brown goes right and
striped goes to the top.
Earthing of an electric cooker
Many electrical appliances have metal cases, including cookers, washing
machines and refrigerators.…read more


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