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**P1.3 The usefulness of electrical appliances**

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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.

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**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.

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**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

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

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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.

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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).

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**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)

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**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)

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**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.

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