# physics_electric power

What is the approximate cost of boiling 1.75 litres of water in a kettle that draws 13 amps at 230 volts for four min-utes, if electricity costs 15 pence per kilo-watt-hour?
A. 1 p
B. 0.5 р
C. 2 p
D.3 p
E.4 p
Thanks！

The problem requires us to calculate the approximate cost of boiling 1.75 litres of water in a kettle that draws 13 amps at 230 volts for four minutes, given that electricity costs 15 pence per kilowatt-hour.

To calculate the cost of electricity, we use the formula:

Cost of electricity (in pence) = Power (in kilowatts) x Time (in hours) x Cost per kilowatt-hour

The power consumed by the kettle is given by the formula:

Power = Current x Voltage

where current is measured in amperes (A) and voltage is measured in volts (V). In this problem, the kettle draws 13 amps at 230 volts, so the power consumed by the kettle is:

Power = 13 A x 230 V = 2990 W (or 2.99 kW)

Note that we converted watts to kilowatts by dividing by 1000. This is because the cost of electricity is typically measured in kilowatt-hours (kWh).

Next, we need to calculate the time that the kettle is on for. The problem states that the kettle is on for four minutes, so we need to convert this to hours by dividing by 60:

Time = 4 minutes / 60 = 0.067 hours

Now we can plug in the values for power and time into the formula for cost of electricity:

Cost of electricity = Power x Time x Cost per kilowatt-hour

We are given that electricity costs 15 pence per kilowatt-hour, so we substitute this value:

Cost of electricity = 2.99 kW x 0.067 hours x 15 pence/kWh

Simplifying this expression gives us the approximate cost of electricity used by the kettle to boil 1.75 litres of water for four minutes:

Cost of electricity = 3.03 pence

Therefore, the approximate cost of boiling 1.75 litres of water in a kettle that draws 13 amps at 230 volts for four minutes, if electricity costs 15 pence per kilowatt-hour, is 3.03 pence.