Current, voltage and resistance · Grade 11
Current is the rate of flow of charge, measured in amps (A). Potential difference (p.d., or voltage) is the energy given to each coulomb of charge, measured in volts (V). Resistance is how hard it is for current to flow, measured in ohms (Ω). They are linked by V = IR, the most used equation in electricity.
Key facts
- V = I × R (p.d. = current × resistance).
- Q = I × t: charge (C) = current (A) × time (s).
- E = Q × V: energy transferred (J) = charge × p.d.
- An ammeter goes in series; a voltmeter goes in parallel (across the component).
- A straight-line I–V graph through the origin means constant resistance (an ohmic conductor).
- A filament lamp’s resistance rises as it heats up; a diode only lets current flow one way.