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Physics Paper 1 (Electricity (circuitSymbols1, Electrical charge:
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Physics Paper 1
Electricity
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Series circuits:
Components that are connected one after another on the same loop of the circuit are connected in series. The current that flows across each component connected in series is the same.
Parallel circuits:
Components that are connected on separate loops are connected in parallel. The current is shared between each component connected in parallel. The total amount of current flowing into the junction, or split, is equal to the total current flowing out. The current is described as being conserved.
Series
Parallel
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Inside a plug
There are three main wires in a plug. The blue, striped, brown (From left to right).
- Blue is the neutral wire.
- Striped is the earth wire.
- Brown is the live wire.
There is a fuse on the right hand side of the plug which breaks the circuit if too much current flows.
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The national grid:
The national grid transmits power via electricity towers across the country, you can normally see these dotted around the various landscapes. They use things called transformers.
A transformer is an electrical device that changes the voltage of an alternating current (ac) supply, such as the mains electrical supply. A transformer changes a high-voltage supply into a low-voltage one, or vice versa.
Atomic structure
Structure of the atom:
At the centre of an atom is a nucleus containing protons and neutrons. Electrons are arranged around the nucleus in energy levels or shells.
Isotopes:
Isotopes are atoms of an element with the normal number of protons and electrons, but different numbers of neutrons. Isotopes have the same atomic number, but different mass numbers. The different isotopes of an element have identical chemical properties. However, some isotopes are radioactive.
Plum pudding model:
An early model about the structure of the atom was called the plum pudding model. The atom was imagined to be a sphere of positive charge with negatively charged electrons dotted around inside it like plums in a pudding. An experiment carried out in 1905 showed the plum pudding model could not be correct.
Alpha particle scattering experiment:
A scientist called Rutherford designed an experiment to test the plum pudding model. It was carries out by his assistants Geiger and Marsden. A beam of alpha particles were aimed at a very thin gold foil and their passage through the foil were detected. The scientists expected the alpha particles to pass straight through the foil, but something else also happened.
Some of the alpha particles emerged from the foil at different angles, and some even came straight back. This meant that the positively charged alpha particles were being repelled and deflected by a tiny concentration of positive charge in the atom.
Types of radiation:
Nuclear radiation comes from the nucleus of an atom. Substances that give out radiation are said to be radioactive. There are three types of radiation:
Radiation can be absorbed by substances in its path. For example, alpha radiation travels only a few centimetres in air, beta radiation travels tens of centimetres in air, while gamma radiation travels many metres. All types of radiation become less intense the further the distance from the radioactive material, as the particles or rays become more spread out,
Alpha radiation is the least penetrating. It can be stopped (or absorbed) by a sheet of paper.
Beta radiation can penetrate air snd paper. It can be stopped by a thin sheet of aluminium.
Gamma radiation is the most penetrating. Even small levels can penetrate air, paper or thin metal. Higher levels can only be stopped by many centimetres of lead, or many metres of concrete.
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Hazards:
Radioactive materias in the environment do expose people to risks.
- The radiation from the material can damage the cells of the person directly. This is damage by irradiation.
- Some of the radioactive material can be swallowed or breathed in. While inside the body, the radiation it emits can produce damage. This is damage by contamination.
Energy
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Wasted Energy:
Energy that is 'wasted', like the heat energy from an electric lamp, does not disappear. Instead, it is transferred into the surroundings and spreads out so much that it becomes very difficult to do anything useful with it.
Useful Energy:
Energy that is used in a way where the wasted energy is collected and then used for another purpose.
Energy efficiency:
Useful output energy transfer / total input energy transfer
Useful power output / total power input
Particle model of matter
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Different changes of state:
A substance must absorb heat energy so that it can melt or boil. The temperature of the substance dos not change during melting, boiling, or freezing, even though energy is still being transferred.
Specific latent heat:
The specific latent heat of a substance is a measure of how much heat energy is needed to melt or boil. It is the energy needed to melt or boil 1 kg of the substance.
energy for a change of state = mass x specific latent heat
E=mL
Temperature on gases:
Imagine a gas is trapped inside a container. If the gas is heated, the particles will gain kinetic energy which will make them move faster. This causes the force on the walls of the container to increase and so the pressure increases.
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