[Music] hi and welcome back to freci lessons. co.uk by the end of this video you should be able to calculate the power of electrical components we saw the idea of power when we looked at energy transfer remember that power is the rate at which energy is transferred the unit of power is the Watt and one watt is an energy transfer of one Jewel per second now over the the course of this topic we've seen that energy is transferred in electrical circuits such as this one the potential difference of 10 volts across the resistor tells us that 10 Jew of energy are transferred per Kum of charge passing through the resistor and the current of 1 ampere tells us that one coolum of charge is Flowing every second now if we know both the potential difference across a component and the current flowing through it then we can calculate the power of the component using this equation the power in watts equals the potential difference in volts multiplied by the current in amp and you need to learn this equation as you're not giving it in the exam here's a triangle for the equation if you prefer to use these so here's a question for you to try calculate the power of the resistor pause the video now and try this yourself okay so the power is the potential difference multiplied by the current we've got a potential difference of 50 volts across the resistor and a current of not .2 amp putting these numbers into the equation gives us a power of 10 wats here's another question for you calculate the power of resistor a pause the video and try this yourself okay in this circuit we've got two resistors in series now the first thing we need to do is work out the potential difference across resistor a remember that potential differences shared between components in series the total potential difference across the cell is 20 volts that means that the total potential difference across both resistors is also 20 Vol resistor B has a potential difference of 15 Vols so resistor a must have a potential difference of 5 volts the current passing through the circuit is .5 amp the power is a potential difference multiplied by the current multiplying five by .5 gives us a power of 2.5 wat and that's our final answer now if we know the current through a component and the resistance of a component then we can calculate the power using this equation the power equals the current squared multiplied by the resistance and again you're not given this in the exam so you do need to learn it here's a triangle if you prefer to use that so here's a question for you to try calculate the power of the resistor pause the video and try this yourself okay so the power equals the current squar multiplied by the resistance resistance the current is .4 amp and the resistance is 50 ohms putting these numbers into the equation gives us a power of 8 watts and that's our final answer remember you'll find plenty more questions on calculating power in circuits in my vision workbook which you can get by clicking on the link above okay so hopefully now you should be able to calculate the power of electrical components [Music]