4.2.1.4 Resistors

Spec reference: 4.2.1 (subtopic).

What you need to know

• Resistors
• Independent variable: circuit type (series, parallel).
• Dependent variable: resistance.
• Control variables: number of resistors, type of power
• source.
• Conclusion: Adding resistors in series increases the total
• resistance of the circuit. In a parallel circuit, the more
• resistors you add, the smaller the resistance.

Self-assessment (checklist)

• I can describe how the current through an ohmic
• I can describe what happens to the resistance of an
• I can describe how the current through a filament lamp
• I can describe what happens to the resistance of a
• I can represent the relationship between the current
• I can describe how the current flows through a diode.
• I can describe what happens to the resistance of a
• I can describe how the resistance of a thermistor
• I can describe how thermistors can be used to control a
• I can explain how the resistance of an LDR changes as
• I can describe how LDRs can be used to control a
• I can explain the design and use of a circuit to measure
• I can recognise and draw graphs that represent
• I can use circuit diagrams to construct appropriate

Key steps (method)

• Identify what the question is testing and use the correct equation/definition.
• Show substitutions and units clearly.

Common mistakes

• Unit conversions, rearranging errors, or quoting a law without applying it.