# Power can be calculated in a number of ways. For domestic appliances, a useful formula is

Question

Power can be calculated in a number of ways. For domestic appliances, a useful formula is:

P=VIP=VI

where PP is the power in watts, VV is the voltage or potential difference in volts, II is the current in amperes.

Remember that we can also relateVV andII through Ohm’s Law,V=IRV=IR, and we can relate current to the movement of charge over time,I=QtI=Qt.

a)

A home appliance is to be connected to a power supply with a voltage of 115 V. The appliance comes with a plug containing a fuse rated as 13 A. This means that if the appliance tries to draw too much current, the fuse will melt and prevent a dangerous amount of electricity making it to the appliance or the user.

What would you expect to be the maximum power rating of the appliance? (In other words: at this voltage, while drawing the maximum allowed current, what is the power being used?)

b)

What is the current flowing through a domestic appliance rated as 1.2 kW when it is connected to a power supply of 230 V and in use?

c)

A lightbulb has the following printed on it:

230 V 120 W230 V 120 W

What is the current that you would expect to find flowing through the bulb when in use?

What is the resistance of the lightbulb when in use?