 P1.3 The usefulness of electrical appliances

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P1.3 The usefulness of electrical appliances

We often use electrical appliances because they transfer energy at the flick of a switch. We can calculate how much energy is transferred by an appliance and how much the appliance costs to run. Candidates should use their skills, knowledge and understanding to: ■ compare the advantages and disadvantages of using different electrical appliances for a particular application ■ consider the implications of instances when electricity is not available. Additional guidance: Candidates will be required to compare different electrical appliances, using data provided.

What have the following got in common?
We often use electrical devices because they transform electrical energy to whatever form of energy we need at the flick of a switch.

Examples of energy transformations that everyday electrical devices are designed to bring about.
Electrical Heat Electrical Light Electrical Sound Electrical Gravitational Electrical Kinetic Electrical Elastic Electrical Chemical Electrical Nuclear Electrical Electrical

Examples of everyday electrical devices designed to bring about particular energy transformations.

Power Power measures how fast energy is transferred. The greater the power, the more energy is transferred in a given time. The power of an appliance is measured in watts (W) or kilowatts (1kW = 1000W). Power = Energy transferred Time Taken Joules (J) P = E t E P t Watts (W) seconds (s) 1 watt is the transfer of 1J of energy in 1s.

What we pay for when we use an electrical appliance is the energy it transfers. Some appliances transfer energy faster than others and so cost more to use. Kettle – fast energy transfer LED screen – slow energy transfer How much energy an appliance transfers depends on: How long the appliance is switched on; How fast the appliance transfers energy (its power).

Energy is normally measured in joules (J).
The total amount of energy, in joules, can be calculated as follows: energy transferred = power X time (joule, J) (watt, W) (second, s) E = P x t Joules (J) E P t Watts (W) seconds (s)

The amount of energy transferred from the mains is measured in kilowatt-hours, called Units:
energy transferred = power X time (kilowatt hour, kWh) (kilowatt, kW) (hour, h) E = P x t Kilowatt hours (KWh), also known as ‘Units’ E P t Kilowatts (KW) hours (h)

The cost of this energy can be calculated using:
Total Cost = Number of Units x Cost per Unit 1 Unit = 1 Kilowatt hour (1 KWh) Electricity meter readings can be used to calculate total cost over a period of time, typically 3 months.