National 5PhysicsSQARevision NotesElectricityOhm’s LawResistance & Temperature

Resistance & Temperature (SQA National 5 Physics): Revision Note

Exam code: X857 75

Katie M

Written by: Katie M

Reviewed by: Caroline Carroll

Updated on

Resistance & temperature

  • The resistance of some components, such as a filament lamp, is not constant

    • It changes with the current in the component

  • The V-I graph for a filament lamp shows that, as voltage increases

    • the current increases at a proportionally slower rate

    • the resistance increases; the steeper the slope, the greater the resistance

Voltage-current graph for a filament lamp

Graph of voltage versus current for a filament lamp, showing a non-linear relationship. Text says: The gradient is increasing which means resistance is increasing.
For a filament lamp, temperature increases as current increases, which causes resistance to increase. This is indicated by the steeper gradient.

  • The resistance of a filament lamp increases as the temperature of the filament increases

  • The current increases at a proportionally slower rate than the potential difference because:

    • the current causes the filament in the lamp to heat up

    • as the filament gets hot, its resistance increases due to the collisions between the electrons and metal ions in the wire

    • this opposes the current, causing it to increase at a slower rate

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    Author
    Reviewer
    Katie M

    Author: Katie M

    Expertise: Physics Content Creator

    Katie has always been passionate about the sciences, and completed a degree in Astrophysics at Sheffield University. She decided that she wanted to inspire other young people, so moved to Bristol to complete a PGCE in Secondary Science. She particularly loves creating fun and absorbing materials to help students achieve their exam potential.

    Caroline Carroll

    Reviewer: Caroline Carroll

    Expertise: Physics & Chemistry Subject Lead

    Caroline graduated from the University of Nottingham with a degree in Chemistry and Molecular Physics. She spent several years working as an Industrial Chemist in the automotive industry before retraining to teach. Caroline has over 12 years of experience teaching GCSE and A-level chemistry and physics. She is passionate about creating high-quality resources to help students achieve their full potential.