Household electricity meters record energy in kilowatt–hour (kWh) rather than in joule. Which statement best explains this practice?
a) A kWh is a unit of power, not energy, so the meter can display it directly.
b) Energy in joules can only be used for mechanical systems, not electrical appliances.
c) The kWh is a larger unit that makes typical domestic energy readings numerically convenient because 1kWh=3.6×106J.
d) Using kWh avoids having to multiply power by time when working out the cost of electricity.