Electricity and magnetism
Ohm's law in a direct-current circuit
Explore the relation I = U/R for a source and ohmic resistor in a direct-current circuit model. Measure current as voltage and resistance vary, then verify .
⚠ The circuit shown is simulated; use low voltage and disconnect power before wiring a real circuit.
Equipment
- Virtual voltage source, resistor, wires, and ammeter
- U and R sliders; I–U plot
Procedure
Measure current as U and R change
Increase voltage U with its slider while keeping R fixed; read I on the ammeter and locate the point on the I–U graph. Then hold U constant, increase R, and observe I decrease. Compare the readings with I = U/R; the electrons move opposite to conventional current. Compare the observed quantities with .
Check the current relationship
Choose two voltage U settings while keeping R fixed, read current on the ammeter, and record the pairs. Check that each point satisfies ; the ideal resistor's characteristic is linear through the origin.
Compare the effect of resistance
Hold U fixed and increase R through several values, recording I and comparing it with U/R. Use the plot and readings to describe how current changes as resistance rises and identify that the model assumes an ohmic resistor. Compare the observed quantities with .