Physics

• Created by: Hanso22
• Created on: 21-06-18 16:16

Transformers

They change the size of the potential difference of an alternating current.

Step-up transformers increase the potential difference.

Step-down transformers decrease the potential energy.

Transformers equation

Vp/Vs=Np/Ns which means

Vp- input potential differenc

Vs- output potential difference

Np- number of coils on primary

Ns- number of coils on secondary

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National Grid

To transmit the huge amount of energy you either need a high potential difference or a high current. With a high current, you lose lots of energy as the wire heats up. So cheaper to boost PD to 400,000V and keep the current low. This makes the national grid efficient.

To get the PD to 400,000V you need a transformer, big pylons with huge insulators. The transformer has to step the PD up for efficient transmission and then one at the end to take down to a safe, usable level.

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Cables

Live wire- Brown it provides the alternating potential difference(230V)

Earth wire- Green and yellow, it's for protecting the wiring and for safety- stops appliance from becoming live. At 0V.

Neutral wire- blue, completes the circuit and carries the current away. Electricity flows in through the live wire and out through neutral wire. At 0V.

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Power formula

Power= current x voltage

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Atomic structure

1804 John Dolton believed the matter was made of tiny spheres and were different for each element.

100 years on J.J Thomson discovered electrons that could be removed from the atom. He thought that there was a sphere of positive charge with electrons in it. Known as Plum Pudding model.

1909- Rutherford fired a beam of alpha particles but some were deflected back the way they came something the plum pudding model could not explain. This meant most of the mass was at the centre of a tiny nucleus which had a positive charge. Known as the Nuclear Model.

Niel Bohr said the electrons orbited at a certain distance known as energy levels.

The nucleus is tiny and is made up of protons and neutrons. Rest of the atom is mostly empty space and negative electrons.

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Isotopes

Isotopes are elements with the same number of protons but a different number of neutrons.

All elements have isotopes but only 1 or 2 are stable. The other isotopes tend to decay into other elements and give out radiation because they try to become stable. A process known as radioactive decay. They spit out ionising radiation from the nucleus known as alpha, beta and gamma radiation. Also, release neutrons when decaying.

Ionising radiation is when radiation knocks off electrons creating positive ions. The ionising power is why it can do this so easily.

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Calculating half life

Half-life is the time taken for the number of radioactive nuclei in an isotope to halve.

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Gloves and Tongs should be used to avoid particles getting stuck to your skin. You even use a protective suit to stop yourself from inhaling them.

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Power formula(2)

Power=Work done/time taken

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Gravitational potential energy formula

GPE= mass x gravitational field strength x height

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Kinetic energy transfer

Conduction is the process where vibrating particles transfer energy to neighbouring particles.

Energy transferred by heating which is transferred to thermal stores of the object. This energy is shared across the kinetic stores of the particles in the object. In the area where it is more heated, the particles vibrate more and collide with each other. These collisions cause energy to be transferred between particles kinetic energy stores.

The process continues till the energy transferred to other side. Then normally to the thermal stores in the surroundings.

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current in resistors (parallel)

The total current flowing around the circuit is equal to the total of all the currents through the separate components.

There are junctions where the current either splits or rejoins. The total current going into a junction has to equal the total current leaving it.

If two identical components are connected then the same current will flow through each component.

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Resistors in series and parallel

Series

The total resistance of two components is just the sum of their resistance.

This is because by adding a resistor the two or more resistors share the total potential difference. The potential difference across each resistor is lower, so the current in each resistor is lower.

The current is the same everywhere so the total current in the circuit is lower when a resistor is added so total resistance increases.

The bigger the resistor the bigger share of total potential difference is.

Parallel

It reduces the total resistance.

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Ohms law

Potential difference(V-volts)= Current(A-amps) x Resistance(ohm, Ω ).

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Internal energy

Internal energy is stored by the particles that make up a system. It is the total energy that its particles have in their kinetic and potential stores.

Heating the system transfers energy to its particles increasing the internal energy. Can lead to a change in state or temp.

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Energy Formula

Energy= Mass x SHC x Temperature change

SHC= specific heat capacity

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Air pressure

Atmospheric pressure is created by air molecules colliding with the surface.

As the altitude increases atmospheric pressure decreases because the atmosphere becomes less dense so there are fewer air molecules to collide with the surface.

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