GCSE AQA Physics P2

What is electric current?

The rate of flow of electrical charge

State the equation linking charge flow, current and time

Charge flow = current x time

What is the unit for electric charge?

Coulombs (C)

What is the unit for electric current?

Amperes (A)

What is potential difference?

The energy transferred per unit charge between two points in a circuit

State the equation linking potential difference, energy transferred and charge flow

Potential difference = Energy transferred / charge flow

What is the unit for potential difference?

Volts (V)

State Ohm's Law

The current through a component is directly proportional to the potential difference across it at constant temperature

State the equation for Ohm's Law linking potential difference, current and resistance

Potential difference = current x resistance

What is the unit for electrical resistance?

Ohms (Ω)

Describe the I-V characteristic of an Ohmic conductor at constant temperature

A straight line passing through the origin, showing resistance is constant

Describe the I-V characteristic of a filament lamp

An S-shaped curve because resistance increases as temperature and current increase

Why does the resistance of a filament lamp increase with temperature?

Higher temperature increases lattice ion vibrations, causing more frequent collisions with moving electrons

Describe the I-V characteristic of a diode

Current flows in one direction only and has very high resistance in the reverse direction

What is a thermistor?

A temperature-dependent resistor whose resistance decreases as temperature increases

What is a Light-Dependent Resistor (LDR)?

A light-dependent resistor whose resistance decreases as light intensity increases

How does current behave in a series circuit?

Current is the same through every component

How does potential difference behave in a series circuit?

Total potential difference is shared between the components

State the rule for total resistance in a series circuit

Total resistance = sum of individual resistances (R_total = R1 + R2)

How does potential difference behave in a parallel circuit?

Potential difference across each branch is identical

How does current behave in a parallel circuit?

Total current is the sum of currents through separate branches

State the rule for total resistance in a parallel circuit

Total resistance is less than the resistance of the smallest individual resistor

What is Direct Current (DC)?

Current that flows continuously in one direction only

What is Alternating Current (AC)?

Current that continuously reverses its direction of flow

What is the frequency and potential difference of UK domestic mains electricity?

50 Hz and 230 V

What color is the insulation on the Live wire?

Brown

What is the function and potential difference of the Live wire?

Carries alternating potential difference from the supply at 230 V

What color is the insulation on the Neutral wire?

Blue

What is the function and potential difference of the Neutral wire?

Completes the circuit and operates at 0 V

What color is the insulation on the Earth wire?

Green and yellow stripes

What is the function of the Earth wire?

Safety wire at 0 V that stops appliance casings from becoming live

What is the purpose of a fuse?

A thin wire that melts to break the circuit if current exceeds a safe limit

State the equation linking electrical power, current and potential difference

Power = current x potential difference

State the equation linking electrical power, current and resistance

Power = current^2 x resistance

State the equation linking energy transferred, power and time

Energy transferred = power x time

State the equation linking energy transferred, charge flow and potential difference

Energy transferred = charge flow x potential difference

What is the National Grid?

A system of cables and transformers connecting power stations to domestic and industrial consumers

What is the role of a step-up transformer in the National Grid?

Increases potential difference and decreases current to reduce energy loss as heat in transmission lines

What is the role of a step-down transformer in the National Grid?

Decreases potential difference to 230 V for safe domestic consumer use

How do insulating materials become electrically charged when rubbed together?

Electrons are transferred from one material to the other by friction

What charge does an object gain if it loses electrons?

Positive charge

What charge does an object gain if it gains electrons?

Negative charge

What force exists between two like electric charges?

Repulsion

What force exists between two opposite electric charges?

Attraction

Where does an electric field exist?

In the region around any electrically charged object

In what direction do electric field lines point?

Away from positive charges and towards negative charges

How does electric field strength change with distance from a charged object?

Field strength decreases as distance from the object increases

What causes an electrical spark between a charged object and an earthed object?

High electric field strength ionises air molecules, making air conductive