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Ohm's law and power

Entry level · Level 2 · Electrical principles
Goal: Relate voltage, current, resistance, power and energy.
Scan: ElectraLab
Name:Group:Date:
V = I · R P = V · I = I² · R = V² / R E = P · t

Exercises

  1. A 23 Ω heating element is connected to 230 V. Calculate the current and the power.
  2. A 60 W lamp runs at 230 V. Calculate the current and its operating resistance.
  3. A 2000 W heater runs for 3 hours. How much energy does it use? At €0.15 per kWh, what does it cost?
  4. A current of 0.5 A flows through a 100 Ω resistor. Calculate the voltage across it and the power it dissipates.
  5. If the same resistor is connected to half the voltage, what happens to the power?
  6. ElectraLab: build a 12 V source with a 240 Ω resistor. Measure the current (meter in series) and calculate the power.
© 2026 Simulath · simulath.com/en/worksheets · Licence CC BY 4.0: copy, adapt and share it crediting "Simulath (simulath.com)".Technical criteria based on Spain's REBT; check your local code.
Simulath · Worksheet 1/5 · Answer key (for the teacher)

Ohm's law and power

Scan: ElectraLab
  1. A 23 Ω heating element is connected to 230 V. Calculate the current and the power.
    I = V/R = 230/23 = 10 A. P = V·I = 230·10 = 2300 W.
  2. A 60 W lamp runs at 230 V. Calculate the current and its operating resistance.
    I = P/V = 60/230 ≈ 0.26 A. R = V²/P = 230²/60 ≈ 882 Ω.
  3. A 2000 W heater runs for 3 hours. How much energy does it use? At €0.15 per kWh, what does it cost?
    E = 2 kW · 3 h = 6 kWh. Cost = 6 · 0.15 = €0.90.
  4. A current of 0.5 A flows through a 100 Ω resistor. Calculate the voltage across it and the power it dissipates.
    V = I·R = 0.5·100 = 50 V. P = I²·R = 0.25·100 = 25 W.
  5. If the same resistor is connected to half the voltage, what happens to the power?
    P = V²/R: at V/2 the power is (V/2)²/R = P/4. It drops to a quarter.
  6. ElectraLab: build a 12 V source with a 240 Ω resistor. Measure the current (meter in series) and calculate the power.
    I = 12/240 = 0.05 A = 50 mA. P = 12·0.05 = 0.6 W. The reading should match the calculation.

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© 2026 Simulath · simulath.com/en/worksheets · Licence CC BY 4.0: copy, adapt and share it crediting "Simulath (simulath.com)".Technical criteria based on Spain's REBT; check your local code.