Edexcel iGCSE Physics -2.10 Resistance and Current- Study Notes- New Syllabus

Effect of Resistance on Current

The current in an electrical circuit depends on the resistance of the components and the applied voltage. Changing the resistance changes how easily charge can flow around the circuit.

Key Relationship

The relationship between current, voltage, and resistance is given by Ohm’s law:

\( \mathrm{V = IR} \)

or

\( \mathrm{I = \dfrac{V}{R}} \)

• \( \mathrm{I} \) = current (A)
• \( \mathrm{V} \) = voltage (V)
• \( \mathrm{R} \) = resistance (Ω)

Qualitative Effect of Changing Resistance

• If resistance increases, the current decreases.
• If resistance decreases, the current increases.
• This applies when the voltage is kept constant.

Resistance opposes the flow of charge. A higher resistance makes it harder for current to flow.

Physical Explanation

• Higher resistance causes more collisions between electrons and atoms.
• More collisions reduce the rate of charge flow.
• This results in a smaller current.

Changing Resistance in a Circuit

• Adding more resistors in series increases total resistance.
• Using a variable resistor allows resistance to be adjusted.
• Heating a filament lamp increases its resistance.

Everyday Examples

• Turning up a dimmer switch increases resistance, reducing current and brightness.
• A longer wire has greater resistance and carries less current.
• A filament lamp draws less current as it heats up.

Key Idea

• Current depends on resistance and voltage.
• Resistance controls how much current flows.
• This effect is qualitative: higher resistance → lower current.

Important Points to Remember

• Voltage must be constant for direct comparison.
• Not all components have constant resistance.
• Filament lamps are non-ohmic.