Work and Power of Current; Joule–Lenz Law; Electrical Safety
Why does a wire get hot, how much energy does a kettle drink, and what keeps a house from catching fire?
Big idea: When electric current flows, it carries energy. That energy does work — it heats a coil, lights a lamp, spins a motor. The rate at which the current delivers energy is its power. In a plain resistor all of that work turns into heat, and the amount of heat obeys the Joule–Lenz law.
By the end of this topic you will be able to:
- calculate the work of electric current with A = UIt;
- calculate power three ways: P = UI = I2R = U2/R;
- use the Joule–Lenz law Q = I2Rt to find the heat released;
- read a device's rating plate and work out its resistance and current;
- convert energy to kilowatt-hours and find the cost;
- explain a short circuit, why a fuse saves the wiring, and the basic rules of electrical safety.