Electricity 4.2.1 Current Resistance and Potential Difference

Electric Current

Current (I) is the flow of charge in a circuit.

Current Measurement

Measured in amperes (A) using an ammeter, which is placed in series.

Current Formula

Q = charge (Coulombs, C), I = current (Amperes, A), t = time (seconds, s)

Potential Difference (Voltage)

Potential difference (V) is the energy transferred per unit charge.

Voltage Measurement

Measured in volts (V) using a voltmeter, which is placed in parallel.

Voltage Formula

V = voltage (Volts, V), E = energy transferred (Joules, J), Q = charge (Coulombs, C)

Resistance

Resistance (R) opposes current flow. Higher resistance = lower current.

Resistance Measurement

Measured in ohms (Ω).

Ohm's Law

V = potential difference (V), I = current (A), R = resistance (Ω)

Resistor

Straight line through origin; Constant resistance.

Filament Lamp

Curve; Resistance increases as temperature increases.

Diode

Current flows in one direction; High resistance in reverse direction.

LDR

More light = lower resistance; Used in automatic lights.

Thermistor

Higher temperature = lower resistance; Used in thermostats.

Aim of Resistance Investigation

To investigate how the resistance of a wire changes with length.

Required Apparatus

Power supply, Ammeter, Voltmeter, Thin nichrome wire, Meter ruler, Connecting wires, Crocodile clips.

Resistance Calculation Method

Calculate resistance (R) using Ohm's Law.

Graph Relationship

The graph should show a directly proportional relationship: longer wire = higher resistance.

Reason for Resistance Increase

Longer wires have more collisions between electrons and atoms, increasing resistance.

Independent Variable

Wire length.

Dependent Variable

Resistance.

Control Variables

Wire type, temperature.