Electricity
Electrical Energy
To calculate energy transferred by electrical devices using power, time, charge and potential difference.
What you will learn
What electrical energy transfer means
How to calculate energy using power and time
How to calculate energy using charge and voltage
How to convert units correctly in calculations
How to compare the energy used by electrical devices
Explanation
Electrical energy transferred can be calculated from power and time or from charge and p.d. Use E = Pt or E = QV, with time in seconds for joules. An appliance transfers energy to useful and unwanted stores; energy bills may use kilowatt-hours rather than joules. Example: A 300 W appliance runs for 6 minutes. Calculate energy transferred. t = 6 × 60 = 360 s; E = Pt = 300 × 360 = 108000 J. Rearrange the relationship before substituting if a different quantity is required. Consider the conditions.