Physic Labs

Electricity and magnetism

Electrical work and power

Track electrical energy converted in a DC load. Verify W=UItW = UIt, P=UIP = UI, and convert units between joules and kilowatt-hours.

Middle school

⚠ The circuit shown is simulated; when measuring a real load, keep current/voltage within component ratings to avoid overheating.

Equipment

  • Virtual DC circuit with a glowing/heating load
  • Sliders for voltage and current
  • Slider for operating time
  • Virtual electricity meter accumulating energy; readouts for P and W

Procedure

  1. Measure power versus U and I

    Set a (U, I) pair with the two sliders and read the power on the display: check P=UIP = UI. Raise U holding I fixed — P grows proportionally, and the load's brightness in the figure changes accordingly.

  2. Accumulate energy over time

    Keep U, I fixed and drag the time slider: the meter accumulates W=PtW = Pt linearly. At t = 60 s with the P measured earlier, verify W=UItW = UIt; record the joule reading.

  3. Convert to kilowatt-hours

    Divide the measured W reading by 3,6×1063{,}6\times10^6 to convert to kWh — the unit on electricity bills. Estimate that a 1000 W load running one hour uses 1 kWh; predict the reading at doubled U before moving the slider.

Simulation

Experiment history

Between 1840 and 1843, James Prescott Joule measured heat released by current-carrying wires and established Q∝I2RtQ \propto I^2Rt — electrical energy converting to heat in a fixed proportion. His work helped found energy conservation; the SI energy unit bears his name. The notion of electrical power P=UIP = UI grew with late-19th-century commercial grids, when the first electricity meters (Oliver Shallenberger, 1888; evolved from ampere-hour meters) allowed billing by consumed energy — ancestor of today's kilowatt-hour "unit".

Related physicists

Georg Simon OhmJames Clerk MaxwellJames Prescott Joule

Related library topics

Electrical work and power