Electrical Circuits Part 1
Electrical Charges can move easily through some substances, such as metals
Electrical current is a form of this charge
POTENTIAL DIFFRERENCE OR VOLTAGE= ENERGY TRANSFERRED/CHARGE
Current-Potential Difference graphs show how a current varies depending on the potential difference across the component.
The resistance of a component can be found by measuring the current through it and the p.d. across it
VOLTAGE=CURRENT X RESISTANCE
The potential difference of cells connected in series is the sum of the p.d. of each cell
Electrical Circuits Part 2
For series circuits:
- The total resistance is the sum of the resistance of each component
- The same current is through each component
- The total p.d. of the supply is shared between the components
For parallel circuits:
- The p.d. is the same across each component
- The total current through the circuit is the sum of the currents through the seperate components
An LED will emit light when current is flowing through it in the forward direction, the use of these is increasing as they require less current than alternative forms of lighting.
When an electrical charge flows through a resistor, its temperature will increase. A lot of energy is lost through heat in filament bulbs, and less so in power saving lamps like CFLs. There is now more choice in terms of energy-saving bulbs than in recent years.
Circuit Diagram symbols
Electrical Circuit Graphs
Household Electricity Part 1
Cells and batteries supply direct current, i.e. passes in the same direction. An alternating current is one that constantly changes direction.
Mains electricity is an a.c. supply.In the UK it has a frequency of 50Hz and is about 230V
A diode can be used for half-wave rectification of a.c.
Most electrical appliances are connected to the mains through a cable and 3-pin plug.
Household Electricity Part 2
If the current becomes too great, the circuit is disconnected through a circuit breaker or fuse in the live wire.
When the current in a fuse exceeds the rating of the fuse the fuse melts, breaking the circuit.
Some circuits are protected by Residual Current Circuit Breakers (RCCBs) which are significantly quicker than fuses. They detect a difference in the current between the live and neutral wires.
Appliances with metal cases are usually earthed, however some appliances are doubled insulated and so do not have an earth wire connection.
Transferring Electrical Energy
The rate an appliance transfers energy is called its power.
POWER=CURRENT X POTENTIAL DIFFERENCE
ENERGY TRANSFERRED= POTENTIAL DIFFERENCE X CHARGE
ENERGY TRANSFERRED FROM THE MAINS= POWER X TIME
The National Grid
The National Grid distributes electricity from power stations to consumers.
For a given power, increasing the voltage reduces the current required, and reduces energy loss in the cables.
Step-up and step-down transformers are what the National Grid use to change voltages, and these are often essential