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Electricity consumption
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True or false? Electrical power is a measurement of how fast energy is converted from one energy form to another.
Leon has a cake in the oven, and is waiting for it to finish baking. He's using his cell phone as a kitchen timer. Oops! Looks like he needs to charge the battery! Now both these devices are connected to the electric grid, and electric current runs through them.
But even though they are connected to identical wall sockets, they don't use the same amount of electricity. What does that mean, using electricity? Let's look at what the oven and the phone charger use the energy for. In the oven, the energy from the electricity is used to generate heat. In the cell phone, the electrical energy is converted into chemical energy.
This is stored in the battery, so that the phone can use the energy later. What electrical devices do, is convert electrical energy into other types of energy. That is what we mean by saying that something "uses electricity". The electrical energy can be converted fast, or slowly. The oven transforms a lot of electric energy into heat in a short amount of time - it has high power.
The cell phone can't handle that much energy at the same time, it would get too hot, and might catch fire. It transforms the electrical energy at a much slower rate - it has low power. How fast the energy is converted - the power - is measured in a unit called Watts. If the power is one Watt, it means that one Joule of energy is transformed every second. One Joule of energy isn't very much.
It's enough to lift an apple from the floor to a table, or heat one gram of water a quarter of a degree Celsius. Most home appliances are marked with their power in Watts. The cell phone charger has a power of 5 Watts. 5 Joules of energy is converted every second. The oven has a power of 2,300 Watts.
It converts the electrical energy 460 times faster than the cell phone charger does! Each second that the oven is turned on, it uses the same amount of electrical energy as the charger does during 460 seconds. That is almost eight minutes! The electric power can differ greatly between different devices, even though they are connected to the same power source.