Physics AQA Electricity GCSE

What is the circuit symbol for a thermistor?

Rectangle with a bent line through

What is the circuit symbol for a variable resistor?

rectangle with an arrow through it

What is the circuit symbol for an LDR

rectangle surrounded by circle with two arrows outside circle on top left

What is the circuit symbol for an LED

BBC symbol inside a circle with an arrow pointing away from it on top right

What is the circuit symbol for a diode

BBC symbol inside a circle

What is required for charge to flow?

Source of potential difference, closed circuit

Q = IT. State terms and units

Q is charge in coulombs, I is current in amperes, T is time in seconds

The greater the resistance....

the smaller the current (given a fixed voltage)

V = IR. State terms and units

V is potential difference in volts, I is current in amperes and R is resistance in ohms

Current through an ohmic conductor..

is directly proportionate to the potential difference

What are the constants in an ohmic conductor?

Resistance and temperature

What does an ohmic conductor look like on a graph of current + voltage?

Straight line

What does a filament lamp look like on a graph of c + v?

S shape

Why does current decrease as resistance increases?

As current increases, electrons (charge) has more energy. When electrons flow through a resistor, they collide with the atoms in the resistor. This transfers energy to the atoms, causing them to vibrate more. This makes it more difficult for electrons to flow through the resistor

What is special about current in a diode? Why?

Current in a diode flows in one direction only as there is extremely high resistance in the opposite direction

Why does resistance increase with wire length?

Electrons have to get past more atoms

How does an LDR work?

In bright light resistance falls, in darkness resistance is highest

Series circuit

Resistance = sum of resistance of all components, Current = flows in one path, same everywhere,Can only switch all components off at once, PD Is shared across all components

Parallel circuit

Components connected separately to power supply,
Can switch components off individually

PD same everywhere

Current splits across branches

Total resistance less than smallest resistor

Mains electricity in the UK

50 Hz, 230v, AC current

What are the colours of the 3 wires in the plug

Live = Brown, Neutral = Blue, Earth = Green + yellow

Functions of live wire

Live = Carries charge, 230V

Function of Neutral wire

Neutral = Completes circuit, 0V

Function of Earth wire

Earth = Only carries charge if fault, prevents case of appliance becoming live

3 Equations for power

P = E/t, P = QV, P = I2xr

Step-Up transformers

Increase PD from power station to NG

Current decreases so less energy is lost

Step-Down transformers

Decrease PD from NG to consumers for safety

Why can't insulators conduct electricity?

No delocalised electrons

Name how electrical energy is transferred by everyday appliances

Kinetic energy for a motor, thermal energy in a kettle

What happens when 2 insulators rub together?

electrons transferred from one to the other, creating a P charge on one and a N charge on the other

How do you draw electric fields?

Act at right angles to objects surface, from positive to negative

What is PD?

Driving force that pushes electrons around a circuit

What happens when current increases in a filament lamp?

As the current increases the temperature of the filament increases so the resistance increases. This means less current can flow per unit pd so the graph gets shallower

What happens to a thermistor when temperature increases?

as the resistance of a thermistor decreased as the temperature increases

Applications of thermistors

Thermostats

Applications of an LDR

Outdoor lighting, nightlights

How can touching a live wire result in electric shock?

Your body is 0V so touching the live wire causes a large p.d. to be produced across ur body between you and the wire. current flows through you. This causes a large electric shock. When the switch is open there is still p.d. in the live wire so if you made contact with the live wire your body would still provide a link between the supply and earth so a current would flow through you

What is the equation linking charge, energy transferred and voltage?

Energy transferred = charge x pd

How many ms in a s?

1000

What is the equation linking current, resistance and voltage?

V = IR

What is the equation linking power, voltage and current

P = IV

How do you prove something is inversely proportional

multiply two separate pairs of values together to get a constant. constants should be the same