Electrical Energy

Electrical Energy

1. Electrical Appliances

   • They transfer electrical energy into whatever form of energy is needed
   • Lamps to produce light
   • Electrical mixers to produce kinetic energy
   • Speakers to produce sound energy
   • Televisions to produce light and sound energy
   • Many electrical appliances transfer energy by heating
   • May be a useful transfer... e.g. in a kettle but energy is often wasted
   • Appliances should be designed to lose as little energy as possible

2. Electrical Power

   • Power of an appliance = Rate at which it transfers energy
   • The unit of power is a Watt (W)
   • An appliance with 1 watt transfers 1 joule of electrical energy to other forms of energy
   • Often a watt is too small a unit to be useful so power may be given in Kilowatts
   • 1 Kilowatt = 1000 Watts
   • Efficiency=(useful power out ÷useful power in) × 100
   • Power=E÷t
   • P = power in Watts
     • E = energy in Joules
       • t = time taken (in seconds) for the energy to be transferred
   • Power is the energy per second transferred or supplied, so we can write the efficiency equation in terms of power:

3. Using Electrical Energy

   • Companies that supply mains electricity charge customers for the amount of electrical energy used
   • Because of the large numbers involved, the joule is not a suitable unit
   • The amount of energy used is measured in Kilowatt-Hour (kWh)
   • A Kilowatt-Hour is the amount of energy that is transferred by a one-kilowatt appliance when used for an hour
   • The amount of energy transferred to a mains appliance can be found using the equation:
   • E = P x t
   • E = the energy transferred in kilowatt-hours
     • P = power of the appliance in kW
       • t = time taken (in hours) for the energy to be transferred
   • The electrical meter in a house records the number of kWh of energy used
   • The cost of electrical energy supplied is found using the equation:
   • total cost = number of kWh x cost per kWh
   • The cost per kWh is given on the electricity bill

4. Cost effectiveness matters

   • To compare the cost effectiveness of different appliances we must consider a number of different costs:
     • Cost of buying the appliance
     • Cost of installing the appliance
     • Running costs
     • Maintenance costs
     • Environmental costs
     • Interest charged on a loan to buy the appliance
   • Many households want to reduce their energy bills
   • They may buy newer, more efficient appliances
   • They could also install materials designed to reduce energy wastage
   • Payback time = Time it takes for an appliance to pay for itself in terms of energy savings