Physics - ELECTRICITY (P2)

Electric Circuits & Current -

What is electric current?

The flow of electric charge, measured in amperes (A).

Electric Circuits & Current -

What is the equation linking charge, current + time?

Q = I x t

Q = charge (coulombs)

I = current (amperes)

t = time (seconds)

Electric Circuits & Current -

What is the current like at different points in a series circuit?

The current is the same at all points in a series circuit.

Electric Circuits & Current -

What is the current like at junctions in a parallel circuit?

The total current entering a junction equals the total current leaving it.

Potential Difference & Resistance -

Define potential difference (voltage).

The work done per coulomb of charge between two points in a circuit.

Potential Difference & Resistance -

State the equation linking potential difference, current, + resistance.

V = IR

Potential Difference & Resistance -

What happens to resistance in a series circuit?

Total resistance is the sum of all individual resistors: Rtotal = R1 + R2 +…

Potential Difference & Resistance -

What happens to resistance in a parallel circuit?

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

Potential Difference & Resistance -

What is a resistor?

A component that limits / controls the flow of electric current.

Required Practical: Resistance -

In the required pracitcal investigating resistance, what variables are measured?

Voltage across + current through the component.

Required Practical: Resistance -

How do you calculate resistance from the practical?

Using R = V/I

Ohm’s Law + IV Characteristics -

What is Ohm’s Law?

The current through an ohmic conductor is directly proportional to the potential difference, provided the temperature remains constant.

Ohm’s Law + IV Characteristics -

Describe the IV graph for an ohmic conductor (e.g. a resistor).

A straight line through the origin (constant resistance).

Ohm’s Law + IV Characteristics -

Describe the IV graph for a filament lamp.

A curve that flattens at higher voltages - resistance increases as temperature increases.

Ohm’s Law + IV Characteristics -

Describe the IV graph for a diode.

Current only flows in one direction, w/ a threshold voltage.

Series & Parallel Circuits -

How is potential difference distributed in a series circuit?

Shared between components - the sum of voltages equals the battery voltage.

Series & Parallel Circuits -

How is potential difference in a parallel circuit?

Each branch receives the full voltage of the power supply.

Series & Parallel Circuits -

What is the effect of adding resistors in series vs. parallel?

In series: total resistance increases.

In parallel: total resistance decreases.

Mains Electricity & National Grid -

What is the frequency + potential difference of UK mains electricity?

50Hz, 230 V.

Mains Electricity & National Grid -

What type of current is used in mains electricity?

Alternating current (AC).

Mains Electricity & National Grid -

What type of current is supplied by batteries?

Direct current (DC).

Mains Electricity & National Grid -

What are the three wires in a UK plug + their colours?

Live (brown), neutral (blue), earth (green / yellow).

Mains Electricity & National Grid -

What is the function of the earth wire?

Provides a path to the ground in case of a fault, preventing electric shock.

Mains Electricity & National Grid -

What does the live wire do?

Carries the current to the appliance at high voltage.

Mains Electricity & National Grid -

Why is touching the live wire dangerous even when the appliance is off?

It still carries potential difference + can cause a shock.

Energy Transfers in Appliances -

State the two equations for power.

Power (P) = Potential difference (V) x Current (I)

Power (P) = Current (I) squared x Resistance (R)

Energy Transfers in Appliances -

State the two equations for energy transferred.

Energy transferred (E) = Power (P) x Time (T)

Energy transferred (E) = Charge (Q) x Potential difference (V)

The National Grid -

Why is electricity transmitted at high voltage across the National Grid?

To reduce current + minimise energy lost as heat in transmission cables.

The National Grid -

What is the role of a step-up transformer?

Increases voltage + decreases current for efficient transmission.

The National Grid -

What is the role of a step-down transformer?

Decreases voltage to safer levels for domestic use.