P2b Applications of Electricity

What is the function of a resistor?

Increases the resistance of a circuit

What is the function of a variable resistor?

Increases the resistance of a circuit, and can be changed

What is Ohm’s law?

the voltage across a conductor is directly proportional to the current flowing through it, provided all physical conditions, such as temperature, remain constant

What is an ohmic conductor?

A conductor that obeys Ohms Law

What does an ohmic conductor do? (2)

The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference (voltage) across the resistor

This means that the resistance remains constant as the current changes, obeying Ohm’s law

What does the current-potential difference graph for an ohmic conductor (like a resistor) look like?

A straight line through 0,0

What does the current-potential difference graph for a filament bulb look like?

A curved line through 0,0

What is the function of a bulb?

Produces light radiation

What does the current-potential difference graph for a diode look like?

A curved line that increases significantly after a certain potential difference

What is the function of a diode?

Allows current to only flow in one direction

What is the function of an LED?

Allows current to only flow in one direction, and produces light radiation

What happens to the resistance of a thermistor when the temperature changes?

The resistance of a thermistor decreases as the temperature increases

What is the function of a thermistor?

Increases the resistance of a circuit depending on the temperature of the surroundings

What happens to the resistance of an LDR when the light intensity changes?

The resistance of an LDR decreases as light intensity increases

What is the function of an LDR?

Increases the resistance of a circuit depending on the brightness of the surroundings

How are thermistors used?

in circuits as thermostats

How are LDRs used?

in circuits to switch lights on when it gets dark

Give four examples of non-ohmic conductors

Diodes, filament bulbs, LDRs, thermistors

What does 'components in series' mean?

The same electrons flow through components in series

What does 'components in parallel' mean?

The same electrons cannot flow through components in parallel because they are on different branches of a circuit

What happens to current through components connected in series?

there is the same current through each component

What happens to the total resistance of components connected in series?

the total resistance of two components is the sum of the resistance of each component

What happens to the potential difference across components connected in series?

the total potential difference of the power supply is shared between the components

What happens to current through components connected in parallel? (2)

the current splits across the components

the total current through the whole circuit is the sum of the currents through the separate components

What happens to the total resistance of components connected in parallel?

the total resistance of two resistors is less than the resistance of the smallest individual resistor

What happens to the potential difference across components connected in parallel?

the potential difference across each component is the same

What colour is the neutral wire?

Blue

What is name of the blue wire in a plug?

Neutral

What colour is the earth wire?

Green and yellow stripes

What is name of the green and yellow striped wire in a plug?

Earth

What colour is the live wire?

Brown

What is name of the brown wire in a plug?

Live

What is the purpose of the neutral wire?

Completes the circuit

What is the purpose of the live wire?

Provides the alternating potential difference

What is the purpose of the earth wire? (2)

Protects the circuit and stops the appliance casing from becoming live

It can also carry current if there is a fault

What is the potential difference of the live wire?

230 V

What is the national grid?

a system of cables and transformers linking power stations to consumers

What is the potential difference of mains electricity?

230 V

What is the frequency of mains electricity?

50 Hz

What type of current is mains electricity?

Alternating current (caused by an alternating potential difference)

What is direct current (d.c.)? (2)

Current flows in one direction around the circuit, due to a direct potential difference

It is supplied by cells and batteries

What is alternating current (a.c.)?

Current changes (alternates) direction

Why does the national grid transmit electricity at very high potential differences?

Less energy is lost, which makes it more efficient

What happens at step-up transformers?

potential difference increased (current lowered)

What happens at step-down transformers?

potential difference lowered (current increased)

Why do we need step-down transformers?

Electricity has to be reduced to mains potential difference (230V) to be safe for use in homes

How are current, resistance and potential difference linked?

current x resistance = potential difference

How are current, power and voltage linked?

Power = voltage x current