Final answer:
To compare the cost of using kettles with different power ratings, simply multiply the power (in kW) by the time of use and the cost per kWh. A kettle with a higher power rating will cost more to operate if both are used for the same duration. Appliance efficiency also affects the overall cost.
Step-by-step explanation:
To compare the cost of using a kettle with a power rating of 2 kW against one rated 1.2 kW, we must look at the energy consumption over a period of time. If we use both kettles for the same amount of time, the 2 kW kettle will consume more energy. For instance, if each kettle is used for one hour, the 2 kW kettle will use 2 kWh of energy, while the 1.2 kW kettle will use 1.2 kWh.
Following the example given, if we assume electricity costs 12.0 cents per kWh, the cost to run the 2 kW kettle for one hour would be 24 cents, while the 1.2 kW kettle would cost 14.4 cents for the same time. This calculation is based on the formula Cost = Power (kW) × Time (h) × Electricity rate.
It's important to note that the efficiency of the appliance will affect actual costs too. According to provided efficiency comparisons, using electricity directly in a household (85% efficient) is more cost-effective than producing energy at the power plant with a combined efficiency of 38%. The 2 kW kettle, therefore, will be more expensive to run both in terms of direct energy consumption and in terms of how that energy was originally produced.