Electricity

Key Issues

Titles

Chapters

• Action and function of a fuse
• Advantages of transmitting electrical power with reduced currents
• Alternating current and direct current
• Alternating current and the mains supply
• Alternating Currents
• An alternating current (a.c.) is one which is constantly changing direction
• An electric current in metals is a flow of electrons
• Appliances with metal cases are usually earthed. The earth wire and fuse together protect the appliance and the user
• calculate the costs of using electricity from meter readings
• Cells and Batteries
• Cells and batteries supply current which always passes in the same direction. This is called direct current (d.c.)
• Choice of fuse for a particular appliance
• Conductors and insulators
• Cost of electrical energy
• Current in a series circuit, applied voltage and circuit components
• describe how circuit breakers protect the user
• describe how double insulation protects the user
• describe how step-up and step-down transformers are used in the transmission of electricity, including the relationship between the number of turns and voltage across the coils
• describe how to wire a fused three pin plug
• Earthed Appliances
• Effect of light intensity on resistance of a light-dependent resistor
• Effect of temperature on the resistance of a thermistor
• Effect of voltage and resistance on currents in circuits
• Electric current generated by a magnet rotating inside a coil and vice versa
• Electrical Appliances
• Electrical Cable
• Electrical Faults
• Electrical heating used in a variety of domestic contexts 28.1 28.1
• Electricity is transferred from power station to consumers along the National Grid
• ELECTROMAGNETIC INDUCTION AND GENERATORS
• Energy from mains supply measured in kilowatt-hours
• Energy is normally measured in joules (J)
• Energy transfer when an electric current flows in a resistor
• Energy transferred = current x voltage x time
• Energy used by domestic appliances and electricity bills
• Examples of energy transformations that everyday electrical devices are designed to bring about
• Examples of everyday electrical devices designed to bring about particular energy transformations
• Function of a residual current circuit breaker
• Function of live, neutral and earth wires and the colour of the insulation on each of these
• HEATING AND THE HOME
• If an electrical fault causes too great a current the circuit should be switched off by a fuse or a circuit breaker
• In the UK it has a frequency of 50 cycles per second (50 hertz)
• Increasing voltage (potential difference) reduces current, and hence reduces energy losses in the cables
• Insulation and double insulation as safety devices
• Intentional Energy Transformations
• Joules
• know the difference between a.c. and d.c.
• Mains electricity is an a.c. supply
• Most electrical appliances are connected to the mains using cable and a three-pin plug
• Power
• Power (watt, W) = energy transformed (joule, J) / time (second, s)
• Power = current x voltage
• Power Stations
• Power, potential difference and current are related by the equation: power (watt, W) = current (ampere, A) x potential difference (volt, V)
• recall that a.c. generators are used in the generation of electricity
• SAFETY FEATURES USED IN MAINS CIRCUITS
• Series and parallel circuits
• The amount of electrical energy a device transforms depends on how long the appliance is switched on and the rate at which the device transforms energy
• The Live Terminal
• The live terminal of the mains supply alternates between positive and negative potential with respect to the neutral terminal
• The National Grid
• The Neutral Terminal
• The neutral terminal stays at a potential close to zero with respect to earth
• The power of an appliance is measured in watts (W) or kilowatts (kW)
• The rate at which energy is transformed in a device is called the power
• The structure of a three-pin plug. Correct wiring of a three-pin plug
• The structure of electrical cable
• The uses of step-up and step-down transformers in the National Grid
• Three-Pin Plugs
• TRANSFORMERS
• TRANSMISSION OF ELECTRICITY
• UK Mains Supply
• UK mains supply is about 230 volts
• understand one-way and two-way switching
• understand the functions of live and neutral wires and how the earth wire and fuse protect the user from electric shock
• understand the meaning of the kilowatt-hour and calculate the cost of using electrical appliances using their power rating
• understand the positioning of switches and fuses on the live side of appliances
• Use of transformers in the National Grid and the advantage and disadvantage of overhead and underground cables
• Variation of current with voltage in resistors, filament lamps and diodes
• Variation of current with voltage in wires, resistors, filament lamps and diodes
• Varied use of the heating effect of an electric current
• Voltage
• Voltage = resistance x current
• Watts and Kilowatts
• When the current in a fuse wire exceeds the rating of the fuse it will melt, breaking the circuit