About this experiment
A resistor converts electrical energy to thermal energy. An ideal current source lets you hold current steady while changing resistance, so the square-law dependence on current is easy to isolate. Read the required source voltage as well as power: keeping current fixed while increasing resistance requires a higher voltage.
Learning goals
- Investigate how current affects electric power while controlling the other variables.
- Use the graph and numerical readings to test a prediction.
- Explain the physical assumptions and where this model stops applying.
How to use it
- 1Set current to 2 A, resistance to 10 Ω and time to 10 s. Verify 40 W and 400 J.
- 2Save the curve and double resistance. Explain why power doubles at fixed current.
- 3Double current at the same resistance. Compare the fourfold power increase.
- 4Set heating time to zero. Why is power nonzero but accumulated heat zero?
The model
Assumptions
- The ideal source maintains the selected current by adjusting its voltage. This is not a fixed-voltage supply.
- Resistance is constant and all electrical energy becomes heat. No temperature, cooling or resistance feedback is calculated.
Try this in class
- Q1How does halving current affect heating power?
- Q2Why can increasing resistance reduce power with a fixed-voltage supply but increase it here?
Frequently asked questions
Why is there no temperature reading?
Heat energy alone does not determine temperature. The mass, heat capacity, phase changes and heat losses would also be needed.
Is the source voltage limited?
This is an ideal source. Real current sources have voltage and power limits and may not maintain the chosen current.