Measure the Current of a Red LED
A breadboard circuit with a red LED and resistor in series, with a bold "I" and a large question mark showing the unknown current to solve for.
Predict how much current flows through a red LED wired in series with a 220 ohm resistor on a 5-volt supply -- then prove your prediction with a multimeter.
Steps
  1. Gather a 5V power source, breadboard, red LED, 220 ohm resistor, jumper wires, and multimeter.
  2. Predict the current: use Ohm's Law (I = V / R) with 3V (5V minus the LED's ~2V) and 220 ohms.
  3. Wire the power source, resistor, and LED in one series loop on the breadboard.
  4. Break the loop at one point and insert the multimeter, set to DC milliamps.
  5. Power the circuit and compare the reading to your prediction.
Stretch Goal Swap in a 330 ohm resistor, recalculate the predicted current, and measure again -- is the LED noticeably dimmer?
Intermediate Card Ohm's Law