Physics Topic 2

What is electric current?

The rate at which electrical charge flows through a circuit.

What is the unit used to measure charge?

Coulombs (C).

What is the unit used to measure current?

Amps (A).

What is the unit used to measure potential difference?

Volts (V).

What is the unit used to measure resistance?

Ohms (Ω).

What is Ohm's Law for a standard wire at a constant temperature?

The current changes at the exact same rate as the voltage (directly proportional).

What does a current

voltage graph look like for an ohmic conductor?

What happens to the resistance of a filament bulb as it gets hotter?

The resistance increases.

What does a diode do?

It only lets current flow in one direction.

What happens to the resistance of a thermistor as it gets hotter?

The resistance decreases.

What happens to the resistance of an LDR as light shines brighter on it?

The resistance decreases.

What happens to current in a series circuit?

The current is exactly the same everywhere in the loop.

What happens to voltage in a series circuit?

The total voltage from the power supply is shared out between the components.

How do you find the total resistance in a series circuit?

Add the resistances of all the resistors together.

What happens to current in a parallel circuit?

The total current splits up into the different branches.

What happens to voltage in a parallel circuit?

Every single branch gets the full voltage from the power supply.

What happens to the total resistance when you add resistors in parallel?

The total resistance becomes less than the smallest single resistor.

What is the voltage and frequency of UK mains electricity?

230 V, 50 Hz

What colour is the Live wire and what is its voltage?

Brown, 230V.

What colour is the Neutral wire and what is its job?

Blue, completes the circuit at 0V.

What colour is the Earth wire and what is its job?

Green and yellow stripes, a safety wire to prevent shocks.

Why is a live wire dangerous even if the appliance is turned off?

It is still connected to the mains grid and carries a dangerous 230V.

What is the unit used to measure electrical power?

Watts (W).

What is the unit used to measure energy transferred?

Joules (J).

What is the National Grid?

The massive network of wires and transformers that links power stations to homes across the country.

What does a step

up transformer do?

Why do we use step

up transformers for long cables?

What does a step

down transformer do?

How is static electricity created?

Friction rubs electrons off one insulating material and onto another.

What charge does an object get if it loses electrons?

A positive charge.

What charge does an object get if it gains electrons?

A negative charge.

What happens if you bring two identical charges together?

They push away from each other (repel).

What happens if you bring two opposite charges together?

They pull towards each other (attract).

What do we call the invisible region around a charged object where it can push or pull things?

An electric field.

Which way do electric field lines point?

Point outwards away from positive, and inwards towards negative.

What causes a static spark to jump?

A high voltage difference forces electrons to leap across the air gap to the ground.

What happens to the air around an object with a massive static charge?

The air gets ionised, turning it into a conductor that can bleed away charge.