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Lesson 1 of 6 · 12 minutes · Free

Voltage, Current & Resistance

Predict current and resistor power before changing the supply or resistance.

Try the experiment ↓Practice challenge ↓

See the idea

Voltage is an electrical potential difference between two points. Current is the rate at which charge passes a point. A resistor converts electrical energy into heat; for an ideal ohmic resistor at a fixed temperature, current equals voltage divided by resistance.

The supply establishes the potential difference across a complete circuit. An ammeter belongs in series with the current path; a voltmeter measures across two nodes. A real ammeter placed directly across a supply can create a dangerous short circuit.

Power matters as well as current. At a fixed resistance, doubling voltage doubles current but quadruples heating power. The bench models an ideal source and resistor, so it does not predict temperature or a real component’s failure.

I = V / R P = VI = V² / R

Voltage drives current; resistance limits it. Always calculate power separately.

Work through an example

  1. Apply 12 V across a 1,000 Ω resistor: I = 12 / 1,000 = 0.012 A = 12 mA.
  2. The resistor dissipates P = 12 × 0.012 = 0.144 W.
  3. At 24 V with the same resistor: I = 24 mA and P = 0.576 W—four times the original power.

Watch for this

Ohm’s law alone is not a model of an LED, motor or regulated electronic load. Their current depends on other characteristics.

Predict, then test

  1. Start at 12 V and 1,000 Ω. Compare the current and power meters with the worked example.
  2. Double voltage, then restore it and double resistance. Observe which changes halve or double current.

Your virtual bench

Change a setting. See the circuit respond.

Swipe the diagram sideways to explore the connections.

±12 VR 1000 ΩReturn reference: 0 V
Source current12 mA
Supply power0.144 W
Resistor voltage12 V
Resistance1,000 Ω

Model: Ideal low-voltage DC source and linear resistors; zero wire resistance except the selected connection fault. Values are calculated, not equipment measurements. Browser simulation only—do not connect live equipment.

Check your understanding

At fixed resistance, doubling voltage changes power by what factor?

Put it to work

Set the bench to produce 20 mA from 12 V. What resistance and dissipation are required?

Show the worked solution

R = 12/0.020 = 600 Ω; P = 12 × 0.020 = 0.240 W. Component selection also needs rating margin and operating-condition checks.

Try the experiment and answer the check, then record your completion.

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