[Music] hi and welcome back to free science lessons. co.uk by the end of this video you should be able to calculate the amount of energy transferred by electrical appliances in the last video we looked at how appliances transfer electrical energy into other forms such as kinetic energy and thermal energy we saw that appliances have a power rating and that tells us how many jeels of energy are transferred every second in this video we're going to learn how to use power ratings to calculate the total energy transferred when an appliance is in use so here's a typical question a kettle has a power rating of 2,200 wats and is used for 80 Seconds calculate the total energy transferred to calculate the energy we use this equation the energy in Jews equals the power in Watts multiplied by the time in seconds here's a triangle for this equation now you're not given this equation in the exam so you need to make certain that you learn it so let's go back to our question we've got a kettle with a power rating of 2,200 wat and it's used for 80 Seconds to calculate the energy we multiply the power by the time so multiplying 2,200 by 80 gives us a total energy transfer of 176,000 Jew now normally when we've got a really large energy value like this one we convert it to kles and to do that we divide by 1,000 that gives us 176 K and that's our final answer here's a question for you to try if fan has a power rating of 20 wats and is used for 1 hour calculate the total energy transferred pause the video now and try this yourself okay so to calculate the energy transferred we multiply the power by the time but remember that the time has to be in seconds 1 hour is 3,000 600 seconds so multiplying 20 by 3,600 gives us a total energy transferred of 72,000 Jew and that's 72 K here's another question for you an ion is used for 5 minutes and a total of 600,000 Jew of energy is transferred calculate the power of the ion pause the video and try this one yourself okay so we're asked to calculate the power of the ion to do that we need to go back to our equation looking at the triangle we can see that to calculate power we divide the energy by the time so in the question the total energy transferred is 600,000 Jew the time is 5 minutes which is 300 seconds dividing 600,000 by 300 gives us a power of 2, Watt and that's our final answer okay here's a final question for you a blender has a power of 400 watts a total of 48,000 Jew of energy is transferred when the blender is in use calculate the time that the blender is used for pause the video now and try this yourself okay looking at the triangle to calculate the time we need to divide the energy by the power so going back to the question the energy is 48,000 Jew and the power is 400 watts dividing 48,000 by 400 gives us a time of 120 seconds and that's our final answer remember you'll find plenty of questions on calculating the energy transferred by appliances in my Orion workbook and you can get that by clicking on the link above okay so hopefully now you should be able to calculate the amount of energy transferred by electrical appliances [Music]