2. Electricity

What is electric current?

Flow of electrical charge, measured as rate of charge flow (Q = I × t).

What is the equation for charge flow?

Q = I × t (charge flow = current × time).

What is potential difference?

Voltage across a component that drives current, measured in volts (V).

What is the equation for potential difference?

V = I × R (potential difference = current × resistance).

What is resistance measured in?

Ohms (Ω).

What does Ohm's Law state?

Current through a conductor is directly proportional to potential difference at constant temperature (V = I × R).

What is an ohmic conductor?

A component where resistance remains constant as current changes.

How does resistance of a filament lamp change?

Increases as filament temperature increases.

How does a diode function in a circuit?

Allows current in one direction, with very high resistance in reverse.

How does a thermistor's resistance change?

Decreases as temperature increases.

What is a common application of a thermistor?

Used in thermostats to control temperature.

How does an LDR's resistance change?

Decreases as light intensity increases.

What is a common application of an LDR?

Switching lights on when it gets dark.

What is required for charge to flow in a circuit?

A closed circuit with a source of potential difference.

What is the same in a series circuit?

Current through each component.

How is total resistance calculated in series?

R_total = R1 + R2.

How is potential difference shared in a series circuit?

Total potential difference is split between components.

What is the same in a parallel circuit?

Potential difference across each component.

How does adding resistors in parallel affect total resistance?

Total resistance is less than the smallest individual resistor.

What is mains electricity in the UK?

Alternating current (AC) at 50 Hz and about 230 V.

What is the difference between AC and DC?

AC alternates direction; DC flows in one direction.

What are the colors of the live, neutral, and earth wires?

Live: brown, Neutral: blue, Earth: green/yellow stripes.

What is the role of the earth wire?

Safety wire that carries current only during a fault.

Why is the live wire dangerous even if a switch is open?

It carries alternating potential difference from the supply.

What is the equation for electrical power?

P = V × I (power = potential difference × current).

What is an alternative equation for power?

P = I² × R (power = current squared × resistance).

What is the unit for power?

Watts (W).

How is energy transferred calculated?

E = P × t (energy = power × time).

What is another equation for energy transferred?

E = Q × V (energy = charge flow × potential difference).

What is the unit for energy transferred?

Joules (J).

What is the National Grid?

A system of cables and transformers linking power stations to consumers.

Why are step-up transformers used in the National Grid?

To increase potential difference for efficient transmission.

Why are step-down transformers used in the National Grid?

To decrease potential difference for safe domestic use.

What are the key circuit diagram symbols?

Include battery, resistor, bulb, switch, ammeter, voltmeter.

How do you measure resistance of a component?

Measure current through and potential difference across it, then use V = I × R.

What is investigated in Required Practical 15?

Factors affecting resistance, like wire length and series/parallel combinations.

What is investigated in Required Practical 16?

I–V characteristics of components like filament lamp, diode, and resistor.