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P5 - Electricity in the home - Coggle Diagram
P5 - Electricity in the home
5.3 - Electrical power and potential difference
Electrical power supplied to an appliance
I - current - A
V - potential difference - V
P - power - W
P=IxV
To get the correct rating for a fuse, work out normal current through appliance using - I=P/V
Energy transferred to a device
P - power - W
E - energy - J
Rearranged - E=Pxt
t - time - s
P=E/t
The power supplied to a device is the energy transferred to it each second.
5.2 - Cables and plugs
In a three-pin plug or a three-core cable, live wire - brown, neutral wire - blue, earth wire - stripped green & yellow.
Earth wire is connected to longest pin in plug and used to earth the metal case of a mains appliance.
A mains cable is made up of two or three insulated copper wires surrounded by an outer layer of flexible plastic material.
Plastic is used because it is a good electrical insulator.
Sockets and plug are made from stiff plastic materials that enclose the electrical connections.
5.1 - Alternating current
To calculate the frequency of an a.c. supply, measure the time period of the waves then use - frequency = 1/time taken for 1 cycle.
The peak potential difference of an a.c. supply id the maximum voltage when measured from zero volts.
The national grid
System of cables & transformers linking power stations to consumers.
Step-up transformers are used to increase the p.d. from power station to transmission cable.
Step-down transformers are used to decrease the p.d. to a much lower value for domestic use.
A mains circuit has a live wire, which is alternatively positive and negative each cycle, and a neutral wire at 0 volts.
Direct current flows in one direction only. Alternating current repeatedly reverses its direction of flow.
5.5 - Appliances and efficiency
Useful energy supplied by a device
Efficiency of device x energy supplied to device
Energy supplied to an appliance
P - power of electrical appliance - W
t - time - s
E - energy transferred to device from mains supply - J
E =P x t
Efficiency may be used as a decimal between 0 - 1 or a %
A domestic electricity meter measures how much energy is supplied to a house.
5.4 - Electrical currents and energy transfer
Energy transferred to a component
V - potential difference - V
Q - charge - C
E - energy - J
E = V x Q
When chare flows through a resistor, energy transferred to the resistor make it hot.
When charge flows around a circuit for a given time, the energy supplied by the battery is equal to the energy supplied to all the components in a circuit.
Charge flow
I - current - A
t - time - s
Q - charge - C
Q=I x t