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Voltage, current and resistance

These exercises use loose AA cells or disconnected, unpowered passive parts only. Do not work on household wiring, mains supplies or high-voltage equipment. Never connect current-mode probes across a battery. Stop if a battery is damaged, leaking or hot.

3 V+−330 ΩLED+−
3 V holder → 330 Ω resistor → red LED → holder. Assemble with batteries removed.
  1. Voltage (V) is potential difference; current (A) is charge flow; resistance (Ω) opposes that flow. In an ohmic resistor, I = V/R. At 3 V across 1,000 Ω, current is 0.003 A: 3 mA.
  2. Power in a simple DC circuit is P = V × I. The example resistor dissipates 0.009 W. Choose a resistor rated above the calculated power and follow component specifications. LEDs are not ohmic resistors; include their forward voltage in circuit calculations.
  3. Measure voltage across a component; measure resistance only after removing power and isolating it. Current measurement is in series and needs different setup. Never bridge battery terminals with current-mode probes.

Related explanations

Volts (V)Amperes (A)Resistance (Ω)Watts (W)

Official sources