A heater gets hot, but the wire that brings the current to it stays cool. A bulb that is rated 100 W uses more electricity than one that is rated 40 W. In this course we find how much heat a current makes, what the power of an appliance means, and how to work out the energy that a house uses and the bill for it.
3 lessons, about 1 h 15 min3 simulations13 problems6 practice questionsPython in every lesson
Created by StemPy LabWhen a current flows through a resistor, the electrical energy changes into heat. The heat produced is , which is also and . The heat is proportional to the square of the current, to the resistance and to the time. Heaters, bulbs and fuses use this effect.
Electric power is the rate at which electrical energy is used or changed to another form: . With Ohm's law, . The unit is the watt, and 1 W = 1 J/s. An appliance marked 220 V, 100 W uses 100 J every second when it works on 220 V.
Electrical energy is . The joule is too small for use at home, so we use the kilowatt hour (kWh), also called a unit: 1 kWh = 3.6 million joule. The bill is the number of units multiplied by the price of one unit. A bulb of 100 W that works for 10 hours uses one unit.
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