How to play Ohm's Law Lab
- Choose a test and read the supply, the resistor, or the meter readings on the card.
- Use V = I·R, or I = V ÷ R, or R = V ÷ I; for the LED, take its 2.0 V away first.
- Type your prediction and press Start. The supply rises, the meters follow, and the I–V graph draws itself.
- Compare the meters and the graph with your orange prediction.
Current, voltage, and resistance
A voltage pushes charge round a circuit and a resistor holds it back. For a fixed resistor at a steady temperature, doubling the voltage doubles the current: the current is proportional to the voltage, and the constant that links them is the resistance, V = I·R. That one rule gives three forms, I = V ÷ R, R = V ÷ I, and V = I·R, so any two of the quantities give the third. Plotted as current against voltage, a resistor gives a straight line through the origin whose slope is 1 ÷ R: a steep line is a small resistance. Not everything obeys Ohm's law. An LED passes almost no current until its voltage reaches about 2 V, and then holds that voltage while the current grows, so it needs a resistor in series to set its current; the resistor gets whatever voltage the LED leaves.
A focused learning model
The resistors are fixed, so their I–V graphs are straight lines through the origin, and the current is steady at once. The supply ramps steadily from 0 to its set voltage over 2 s and holds for 1 s; the meters are ideal and the wires have no resistance. The LED is ideal: no current below 2.0 V, then a constant 2.0 V drop (real LEDs vary). The electron dots move at a speed in step with the current, not at the real drift speed. Answers within 2% are right.