How to play Fuse Test
- Choose a test and read the supply, the load, and the fuse on the card.
- Use I = V ÷ R, R = V ÷ I, or V = I·R; for a limit, set the current exactly to the fuse's rating.
- Type your prediction and press Start. The supply rises, the fuse warms, and it holds or melts.
- Compare the ammeter, the fuse, and the graph with your orange prediction.
Ohm's law and fuses
Ohm's law, I = V ÷ R, says how much current a voltage drives through a resistance, and that current heats every wire it passes through. A fuse is a deliberately thin wire placed in the circuit: when the current reaches its rating it melts and breaks the circuit before the wiring overheats. That is why a fuse sets limits. On a 12 V supply, a 2 A fuse allows nothing below 6 Ω, and a resistor rated for 0.1 A can take at most 0.1 × 47 = 4.7 V. The lower the resistance, the larger the current: join a battery's terminals with a thick wire and only its own small internal resistance holds the current back, so hundreds of amperes can flow. A fuse protects the wiring, not people: through wet skin, 230 V drives a few hundred milliamperes, far too little to melt a 13 A fuse but enough to stop a heart, which is why homes also have residual-current devices.
A focused learning model
Every resistance is fixed, the wires and the ammeter are ideal, and a battery's internal resistance is counted only where it is given. The supply ramps steadily from 0 to its voltage over 2 s; the fuse melts the exact moment the current reaches its rating (a current within 0.05% of the rating counts as holding), and a fuse that holds is watched 1 s more. Real fuses take a little time to melt and can carry a small overload for a while. These are teaching values, not safety limits: never test mains electricity or skin. The electron dots move at a speed in step with the current, not at the real drift speed. Answers within 2% are right; a limit must hold with at most 2% to spare.