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Electricity lab: why power lines use high voltage

Why do pylons carry 11 000 or 33 000 volts when homes use 230 V? Send power to a town and find out where the energy goes.

▶ Start the lab🧠 Questions📄 My report
P lost = I² Rhigh V → low I
LevelS4 to S6 (and IGCSE, A Level)
TimeAbout 35 min
You useP = VI, P = I²R, transformers
PriceFree: no account

🎯 Aim

To investigate how the transmission voltage affects the current and the power lost in cables, and to use the transformer equation.

You will learn to

  • Calculate current with I = P ÷ V.
  • Calculate power losses with P = I² R.
  • Use the transformer equation Ns ÷ Np = Vs ÷ Vp.
  • Explain why the National Grid uses high voltage.

🧭 What to do

  1. Set 200 kW, 230 V and 10 km: how much power arrives?
  2. Choose 11 kV, then 33 kV: compare the losses.
  3. Change the Length of the line and watch the graph.
  4. Read the turns ratio of the step-up transformer.
  5. Answer the questions with the class data.
  6. Write your conclusion and download your lab report.

🔬 Lab bench

📋 The data

Current and power lost when 500 kW is sent 20 km at different voltages.

🧠 Investigate: answer from the data

Type your answer and tap Check. Use 💡 Hint first; open the method only when you are stuck.

📄 My lab report

Your report collects the aim, your data table, the graphs, your answers and your conclusion. It is made on your phone or computer: nothing is sent to anyone.

Check your conclusion

For the same power, a higher voltage means a smaller current (I = P ÷ V). The power lost in the cables is I²R, so making the current 3 times smaller makes the loss 9 times smaller. At 230 V almost all the power would be lost over long distances, so electricity is sent at 11 kV, 33 kV or more and stepped down to 230 V for safe use in homes.

➕ Get more from this experiment

📝 Free

Print the worksheet (button above), download the data, and save your report. Teachers can project this page in class.

📦 Premium Lab Pack

1 000 RWF

  • Worksheet: transmission and transformer calculations
  • Model power line practical with resistance wire
  • Teacher guide and answer key
  • Exam-style questions with marking scheme
See the pack

👩‍🏫 For teachers

Use it as a practical when apparatus is missing, as homework, or as a project. Free lesson plans help you plan, teach and assess.

🔗 Related in the subjects

Home electricity labHydropower labElectromagnetic inductionPhysics home

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