This deep dive covers Understanding Resistance and Ohm's Law within Resistance & Ohm's Law for GCSE Physics. Revise Resistance & Ohm's Law in Electricity for GCSE Physics with 16 exam-style questions and 30 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 2 of 16 in this topic. Use this deep dive to connect the idea to the wider topic before moving on to questions and flashcards.
📚 Understanding Resistance and Ohm's Law
Ohm's Law states that the voltage across a component is directly proportional to the current through it, provided temperature stays constant: V = I × R (Voltage in volts = Current in amps × Resistance in ohms). Rearranged: R = V ÷ I (to find resistance) and I = V ÷ R (to find current). A component is ohmic if it obeys this law at constant temperature (e.g. a resistor). A component is non-ohmic if resistance changes with conditions (e.g. a filament bulb — resistance increases with temperature; a diode — only conducts in one direction).
Resistance is a measure of how much a component opposes the flow of current.
Unit: Ohms (Ω) — named after Georg Ohm
- Higher resistance → lower current (for same voltage)
- Higher voltage → higher current (for same resistance)
- R = V / I (the most useful rearrangement)
Practice questions for Resistance & Ohm's Law
Which of the following best describes electrical resistance?
Explain what is meant by an ohmic conductor.