What is Joule effect?

Also known as: fuse

Definition 12.14 High School Physics · Chapter 12 — Electric Circuits and Power

The dissipation $P = RI^2$ turning electrical energy into heat in every resistor is the Joule effect. Heaters, kettles, toasters and old-style bulbs are resistors by design; a fuse is a thin wire calibrated to melt — opening the circuit — when the current exceeds its rating.

The delivery of : raising U at fixed P = UI shrinks I, and the loss falls with I2. — The delivery of Example 12.15: raising $U$ at fixed $P = UI$ shrinks $I$ , and the loss falls with $I^2$ .

Examples

Example 12.15 (Why pylons run high)

A village needs $P = 100\,\mathrm{kW}$ through a line of resistance $R_\ell = 5.0\,\Omega$ . Delivered at $U = 500\,\mathrm{V}$ : $I = P/U = 200\,\mathrm{A}$ and the line wastes $R_\ell I^2 = 200\,\mathrm{kW}$ — twice the delivery: absurd. At $U = 20\,\mathrm{kV}$ : $I = 5.0\,\mathrm{A}$ and $R_\ell I^2 = 125\,\mathrm{W}$ . Forty times less current, $1600$ times less loss.

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Examples

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