# Physics P2 Electricity

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- Created by: Dominic Hayward
- Created on: 16-05-13 16:22

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- Electricity
- Static Electricity
- Some insulating materials become electrically charged when they are rubbed together.
- Charges that are the same repel while opposite charges attract.
- When you rub 2 insulators together they become electrically charged
- This only works for insulated objects as metals arer easily earthed.

- When the materials are rubbed against each other:
- The material that gains electrons becomes negatively charged
- The material that loses electrons becomes positely charged
- Both materials gain an equal amount of charge, but are opposite.
- The material that gains electrons becomes negatively charged

- Both materials gain an equal amount of charge, but are opposite.
- Negetively charged particles called electrons move from one material to the other.

- Two charged objects will repel if they have the same charge
- If one object is charged you can check by seeing if small uncharged objects are attracted

- Current and Voltage
- For a curcuit to work there must be a complete circuit and no short circuits
- Series circuits are circuits where all the components are attached by the same wire-and the current is the same
- Parallel circuits are circuits where electrons can go multiple ways in a complete circuit-so it is shared.
- Electric current is a flow of electric charge and is measured in amperes which is measured by an ammeter
- Calculating current I=Q/t (I is current in amps, Q is charge in coulombs and t is time in seconds)
- Potential difference, voltage, is needed to make a current go through it. It is measured in volts and measured with a voltmeter.
- Calculating charge V=W/Q (V is voltage in volts, W is work done in joules and Q is charge in coulombs)
- A cell produces a voltage of 1.5V in a current and when more is connected, the more potential difference.

- Resistance
- Resistance is measured in Ohms. The total resistance is all the componants resistances added together.
- There is a resistance to the flow of electric current through most conducters
- The resistance of the wire increases as the length of the wire increases and the thickness of the wire decreases.
- An electric current flows when electrons move through a conductor and when the electrons collide with ions it is more difficult for current to flow and causes resistance.
- The resistance of a long wire is big because the electrons collide with ions more often.
- The resistance is higher in a thin wire because there are fewer electrons to carry the current.

- The equation for current is V=I*R (V is voltage in volts, I is current in amps and R is resistance in Ohms)
- A current flowing through a resistor at a constant temperature is directly proportional to the p.d across it.
- A filament lamp is a type of light bulb and when current goes through it it creates an S shape on the graph.
- A diode has high resistance in 1 direction which means the graph is at zero until enough current flows through it.

- Household Electricity
- Direct current is where the current can only flow in one direction eg. batteries and cells
- Alternating current is where the current is constantly changing direction and a frequency of 50Hz.
- The blue wire is neutral, the brown wire is live and green/yellow is earth
- The plug
- There is a fuse
- The pins are made from brass to conduct electricity
- The fuse can break at high current
- The case is made from rubber.
- A cable grip holds the wires down.

- Fuses protect electrical appliances by blowing if too much current passes through them. It contains a wire which melts easily.
- Fuses are usually 3A, 5A and 13A
- Circuit breakers protect an electrical appliance by switching off the appliance if too much current is supplied

- Earthing protects appliances by connecting to metal areas and any current on the wire will be sent to the fuse.

- Current, Charge and Power
- Electric appliances are changed in order to make them more efficient as it makes the appliance more useful
- Power is a representation of how much energy is transferred in a given time.
- P=E/t (P is the power in watts, E is the energy transferred in joules and t is time in seconds.)
- E=V*Q (E is energy transferred in joules, V is voltage in volts and Q is charge in Coulombs)

- Static Electricity

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