Physics GCSE, unit two Electricity

Physics GCSE, unit two Electricity

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• Created by: jesper
• Created on: 18-03-12 07:00

Ampere (A)
Current (I)
Coulomb (C)
Charge (Q)
Joule (J)
Energy (E)
Ohm (Ω)
Resistance (R)
Second (s)
Time (t)
Voltage (V)
Volts (V)
Watt (W)
Power (P)

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Hazards of electricity

Frayed cables= can expose metal wires and touching these could give an electric shock. It could also be a possible cause of fires

long cables= are a danger because someone can trip over them. If put in a bunch, the high current will cause it to heat up and eventaully cause a fire.

Damaged plugs= could lead to exposure of parts which are carrying electricty.

Water around sockets= water conducts electricity at high voltages, touching the water can cause an electric shock.

Pushing metal object into sockets= metals conduct electricity. Pushing a metal object into a socket can cause in an electric shock or death.

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Safety features

Double insulation= electric parts will be covered with plastic which does not conduct electricity and will prevent the user from receiving a electric shock.

Earthing= Metal casing should be connected to the eath wir so that if the live wire becomes frayed or breaks and comes in contact with the casing, the earth wire provides a low resistance path for the current so that the electricity can pass down to the eath without giving the user an electric shock.

Fuses= if a too large current flows through the circuit the fuse melts stopping the current from flowing so preventing a shock.

Circuit breakers= is the same as a fuse ony it does not need to be replaced just resetted.

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Resistors and Resistance

Resistors are used in circuits to control the size of the currents and voltages.

Fixed resistors= they have a fixed amount of resistance.
Variable resistors= resistance can be varied either increased or decreased. It is used in remote controls and also to control the speed of a motor.

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Ohm's law

Voltage (V) = Current (A) x Resistance (Ω)

V = IR

Ohm’s Law: The current that flows through a conductor is directly proportional to the potential difference (voltage) across its ends, provided its temperature remains the same

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Devices

Diodes

Diodes are resistors that direct the flow of current to one direction only.

Light-Dependent Resistors (LDR)
LDRs(light-dependent resistors) are used to detect light levels, for example, in automatic security lights, photographic equipment, automatic lighting controls and burglar alarms.

Thermistors

Thermistors are used as temperature sensors, for example, in fire alarms.

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AC and DC

Alternating Current

• The flow of electricity is constantly changing direction.
• Mains electricity supply provides alternating current.

Direct Current

• The flow of electricity is in one direction.
• Cells and batteries provide this.

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Parallel and Series Circuits

Parallel Circuits

Parallel circuits have branches so there are more paths for the current to flow. This means that it is possible to turn different parts of the circuit on or off by using switches. The voltages across components in a parallel circuit are all equal.

Series Circuits

In a series circuit, current is the same throughout the circuit. The size of the current depends on the voltage supplied and the number and nature of the other components in the circuit. If more bulbs are added, there will be a greater

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Voltage and Current

Measuring Voltage and Current

Voltage

ü  Use a voltmeter.

ü  The voltmeter must be connected in parallel.

Current

ü  Use an ammeter.

ü  The voltmeter must be connected in series.

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Power

Power (W) = Current (A) x Voltage (V)

P = I x V

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Energy transferred

Energy Transfer

Energy Transferred (J) = Current (A) x Voltage (V) x Time (s)

E = I x V x t

Explaining Charge, Current and Voltage (cont.)

Current:

ü  The rate of flow of charge/electrons
ü  Is equivalent to one coulomb per second

Voltage:
ü  Energy transferred per unit charge passed
ü  Joule per coulomb
ü  Is the force that pushes the current around the circuit

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Electric Charge

Electric Charge

Insulating materials can be given an electric charge by rubbing them –or charging by friction. This does not create charge, but separates them.

When two uncharged insulators (a plastic rod and a cloth) are rubbed together, electrons from the rod would be rubbed onto the cloth, making the cloth negatively charged and the rod positively charged. Remember, it’s the electrons that move, not protons.

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