Resistance and Special Components

This lesson covers the factors affecting resistance of a wire, the core practical on investigating resistance, and the applications of LDRs and thermistors — as required by the Edexcel GCSE Physics specification (1PH0).

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Factors Affecting the Resistance of a Wire

The resistance of a wire depends on four factors:

Factor	Effect on Resistance	Explanation
Length	Longer wire = more resistance	Electrons must travel further, encountering more collisions with metal ions
Cross-sectional area	Thinner wire = more resistance	Fewer paths for electrons to flow through — like a narrower pipe carrying less water
Material	Different materials have different resistivities	Some materials (e.g. copper) have many free electrons; others (e.g. nichrome) have fewer
Temperature	Higher temperature = more resistance (for metals)	Metal ions vibrate more at higher temperatures, causing more collisions with electrons

Key Relationships

• Resistance is directly proportional to length: if you double the length, you double the resistance.
• Resistance is inversely proportional to cross-sectional area: if you double the area, you halve the resistance.