Resistance and Current

While 12V is generally safe, this battery can deliver hundreds of amps if shorted. Use proper gauge wire for connections to prevent cable heating. Never create a direct short across battery terminals with low-resistance conductors—always use the thin wire mounted in the switch. Check battery connections are secure to prevent arcing.

The wire will reach temperatures exceeding 800°C and will remain hot for 30-60 seconds after disconnection. Clear all flammable materials (paper, cloth, plastic) from the demonstration area. Use fire brick or ceramic tile as a base. Have a fire extinguisher accessible. Do NOT touch the wire or switch mechanism until fully cooled (2-3 minutes). Disconnect by removing battery clips, never by opening the hot switch.

Automotive batteries contain sulfuric acid and can produce explosive hydrogen gas. Ensure adequate ventilation. Do not create sparks near battery terminals. If battery shows signs of damage, leaking, or swelling, do not use. Wear eye protection when connecting/disconnecting terminals.

Purpose

Shows that electrical hazard depends on current, not voltage alone. Touching a 12V car battery with your hand is safe (~1 MΩ body resistance, ~12 μA), but shorting the same battery through a thin iron wire (~0.5 Ω) produces enough current to heat the wire to incandescence. A dramatic illustration of $$I = V/R$$ .

Optima car battery with red top connected by yellow cables to a wooden board holding a knife switch with thin iron wire mounted across the terminals

Figure 1: 12V car battery connected to a knife switch with thin iron wire. Closing the switch sends high current through the wire, heating it to incandescence.

Warning: Electrical Hazard: Low Voltage, High Current

Warning: Burn and Fire Hazard

Warning: Battery Handling

Purpose

Safety Warnings

Warning: Electrical Hazard: Low Voltage, High Current

Warning: Burn and Fire Hazard

Warning: Battery Handling

Purpose