GCSE Physics: P5 - Electricity in the home

What energy transfers occur in a blender?

- electrical energy

- is transferred to kinetic energy in the motors

- in order to mix food

What energy transfers occur in a fan?

- electrical energy

- transfers to thermal energy

What energy transfers occur in an iron?

- electrical energy

- transfers to thermal energy

What energy transfers occur in a kettle?

- electrical energy

- transfers to thermal energy

What energy transfers occur in a hair dryer?

- electrical energy

- transfers to kinetic energy of the electric motors

- and thermal energy in the heater element of the hairdryer

What energy transfers occur in a washing machine?

- electrical energy

- transfers to kinetic energy of the electrical motors

- and thermal energy

What is power?

the rate at which energy is transferred

1 watt (W) is an energy transfer of....

.... 1 joule (J) per second

Which appliances have high power ratings?

- appliances designed to generate thermal energy usually have a much higher power rating

- than appliances designed to generate kinetic energy

What is the power rating of an appliance?

how many joules of energy an appliance transfers in a second

What is the equation for energy transferred by an appliance?

Energy transferred (J) = Power (W) x time (s)

E = Pt

P = E/t

t = E/P

What are the equations for calculating the power of an electrical component?

Power (W) = Potential difference (V) x Current (A)

P = VI

Power (W) = (Current)^2 (A) x Resistance (Ω)

P = I^2 R

What is direct current (DC) ?

where the current only ever flows in one direction

What is alternating current (AC) ?

where the current is constantly changing direction

What are the advantages of alternating current?

- it is very easy to use a transformer to increase or decrease the potential difference of alternating current

- it is harder to do this with direct current

What is the frequency of alternating current in the UK?

frequency of alternating current in the UK = 50 hertz (Hz)

What is the potential difference of alternating current in the UK?

potential difference of alternating current in the UK = 230 volts (V)

What is the equation for calculating frequency from an oscilloscope?

Frequency (Hz) = 1 / time (s)

How are electrical appliances connected to the mains electricity supply?

- in the UK,

- electrical appliances are connected to the mains electricity supply

- using a three-core cable

What does a three-core cable contain?

- a three-core cable contains 3 wires made of copper

- copper conducts electricity

- however, the coating of the wires is made of plastic, which does not conduct electricity

What are the wires in a three-core cable?

- the live wire

- the neutral wire

- the Earth wire

What colour is the live wire?

- the live wire is brown

What colour is the neutral wire?

- the neutral wire is blue

What colour is the Earth wire?

- the Earth wire is green/yellow

What is the function of the live wire?

- the live wire carries the alternating potential difference from the supply

- the live wire is connected to a fuse in the plug

- the live wire has a potential difference of 230 V

What is the function of the neutral wire?

- the neutral wire completes the circuit

- and has a potential difference of 0 V

What is the function of the Earth wire?

- the Earth wire is a safety wire

- that stops the appliance from becoming live

What is the circuit symbol for a fuse?

Fuse

How is the live wire dangerous?

- the live wire is extremely dangerous and can be fatal if touched

- if someone touches a live wire, a current flows through the person into the earth and the person gets electrocuted

Why are appliances with a metal case dangerous?

- appliances with a metal case can be very dangerous

- if the live wire comes loose and touches the metal case,

- the case can become live and give someone a fatal electric shock

How can we prevent an electric shock from a metal case where the live wire has come loose?

- an Earth wire is connected into the ground with a metal rod

- if the metal case becomes live,

- a huge current flows to the Earth and causes the fuse to melt and the current to be shut off

- this prevents anyone from getting an electric shock

What is the national grid?

a system of transformers and high-voltage cables that connects the power stations to the homes

Why is energy lost in power cables?

- energy is always lost in the power cables due to the resistance of the wires

How does distance affect energy loss in power cables?

- the greater the distance between the power stations and the homes,

- the greater the energy loss

Describe an ineffective method of reducing energy loss

- energy loss in power cables could be reduced by buildings power stations nearer to homes

- however, people won't want to live near power stations due to noise and visual pollution

How can transformers be used to reduce energy loss in power cables?

- electricity passes through step-up transformers, which increase the potential difference to several hundred thousand volts and decrease the current of electricity for energy-efficient transmission

- less energy is lost in the power cables when the potential difference is very high

- finally, electricity passes through step-down transformers, which reduce the potential difference to around 230 V, a safe, usable level, before it reaches homes

Describe the diagram of a three-core cable