Six original Cambridge-style questions on the kilowatt-hour: energy in kWh, the cost of running appliances, converting watts to kilowatts and minutes to hours, and the kilowatt-hour in joules.
State what is meant by a kilowatt-hour, and state whether it is a unit of power or of energy.
A 3 kW electric shower is used for 0.5 hours. Calculate the energy it transfers in kilowatt-hours.
E = 1.5 kWh
Electricity costs 30 cents per kilowatt-hour. Calculate the cost of using 6 kWh of energy.
cost = 180 cents = $1.80
A 100 W lamp is left on for 4 hours. Calculate the energy used in kilowatt-hours, and the cost at 30 cents per kWh.
E = 0.4 kWh, cost = 12 cents
change watts to kilowatts first
Show that one kilowatt-hour is equal to 3.6 × 10⁶ J.
E = 3 600 000 J = 3.6 × 10⁶ J
1 kW = 1000 W, 1 h = 3600 s
A family runs a 2 kW heater for 2 hours and a 0.5 kW television for 4 hours in one evening. At 30 cents per kWh, calculate the total cost.
total cost = $1.80
Mark this once you have attempted all six and checked your working. It records a Practiced badge on the topic and adds a one-time bonus. Revealing the solutions alone does not count.