P1.3 Transferring Electrical Energy

• Electrical appliances - extremely useful, transfer electrical energy to other forms of energy
• Common electrical appliances: lamps, electrical mixers, speakers, tvs
• Many electrical appliances transfer energy by heating - useful in things eg. kettles, but energy is often wasted - appliances designed to waste as little energy as possible

• Power - rate at which appliance transfers energy
• E is energy transferred in kilowatt-hours, kWh
• P is power in kilowatts, kW
• t is time in hours, h

or

• E is energy transferred in joules, J
• P is power in watts, W
• t is time in seconds, s

Power Formula: Work Done (j) / Time Taken (s) = Energy Transferred / Time Taken 

To calculate the cost of mains electricity given the cost per kilowatt-hour.

Power (W) = energy transferred (J) / time taken (s)

The more powerful a device is, the faster the rate at which it transforms energy.  

Energy transferred (kWh) = power (kW) × time (h)

Total cost = number of units × cost per unit