In today's video, we're going to take a look at what power is and see how we can calculate it. Now, although they both mean pretty much the same thing, it's important to know that there are actually two different definitions for power, each with their own equation. One is that power is the rate at which energy is transferred which can be shown by the equation power equals energy transferred divided by the time it took to transfer that energy. The other definition is that power is the rate at which work is done and this can be written as power equals work done over time. Now the term work done can be a bit confusing but basically it's just a special measure of the energy transferred and is used when a force is used to move an object by a certain distance. For example, if you pushed a car down the road, then the energy that was required would be referred to as the work done as you moved it a certain distance. Whereas if electrical energy was transferred from a plug socket to your phone, we' refer to that as just energy transferred as there's no force or movement involved. In both cases though, power is measured in watt, energy transferred and work done are measured in jewels, and time is measured in seconds. To see how the equations work, let's compare two lamps to see which of the two is most powerful. The lamp on the left transfers 1,200 JW over 20 seconds, while the other one uses 1,500 JW over 30 seconds. In this case, we'd be using the energy transferred version of the power equation as there's no work being done. For the left lamp, we'd do 1,200 jewels divided by 20 seconds to give us 60 watts as the power. And for the right lamp, we'd divide 1,500 jewels by 30 seconds to give 50 W. So, we can tell that the left lamp is more powerful. If you look on your lamp at home, there may well be a label telling you its power. Let's now try a slightly harder example. If an 1100 W microwave is on for 3 minutes, how much energy is transferred? First, we need to take our energy transferred equation and rearrange it to get energy transferred by itself. If we put the equation into a formula triangle like this, we can see that energy transferred would be equal to power* time. We also need to change our 3 minutes to 180 seconds by multiplying it by 60. And finally, we can substitute our values into the equation and do 1100 * 180 to give us 198,000 Jew. And whenever we have a big number like this, we can convert it to KJ by dividing it by 1,000. So we would have 198 kJ as our answer. As a last example, imagine that to push a car down the street, you have to do 9 kJ of work over the course of 20 seconds. How much power were you using? Once we have the equation, we can see that all we have to do is divide the work done, which is 9 kJ or 9,000 Jew, by the time taken of 20 seconds. So, the power would be 450 W. If you haven't heard yet, you can find all of our videos on our website, cognito.org. You'll also find questions, flashcards, exam style questions, and pass papers. And we track all of your progress so that you always know what to study next. So sign up for free by clicking here or browse our playlist here on YouTube.