# Shared Flashcard Set

## Details

P1a.3
Physics, Core (P1, A3), Electrical Energy
15
Physics
06/19/2008

Term
 What is electrical energy?
Definition
 Energy transfer due to an electric current.
Term
 Why is electricity so useful?
Definition
 It can be converted into almost any other type of energy.
Term
 What is Current?
Definition
 The flow of electrons round a circuit
Term
 What do you need for a current to flow?
Definition
 A complete circuitPower Source (Battery)
Term
 How is current measured?
Definition
 In amps, using an ammeter
Term
 What is resistance?
Definition
 Opposition to the drive of charge.
Term
 What is voltage?
Definition
 The energy used to move charges around. Like "Electrical pressure" Voltage = Current x Resistance.
Term
 How can the current in a circuit be changed?
Definition
 If you increase the voltage, the current goes up.If you increase the resistance, the current goes down.
Term
 How do we measure the power of devices? What is it?
Definition
 Power (in Watts, W) = energy transferred (in Joules, J) / Time taken (In seconds, S).  This power is the rate of energy transfer1 Watt = 1 J/s1 Kilowatt = 1000 watts.
Term
 How can we work out the energy supplied to a device?
Definition
 Energy transferred (kW h, Kilowatt-hours) = Power of device (kW) x Time in use (hours, h)
Term
 How can we use kW h to calculate the cost of electricity?
Definition
 Total cost = number of kW h used x cost per kW h
Term
 What is the national grid?
Definition
 A network of cables connecting power stations to homes and other buildings.
Term
 Why does the national grid need transformers?
Definition
 Transmitting electricity at a high voltage reduces power loss making it more efficient. We use step-up transformers to step this voltage up to the grid voltage. We use step-down transformers at local substations to step the grid voltage down to 230 volts for use in homes and offices.
Term
 Why does increasing the voltage reduce wasted energy?
Definition
 To transmit a lot of electrical power you need a high voltage or a high current because Power = Current X Voltage. However, when we increase the current then the cables become very hot which is a waste of energy. Therefore it is cheaper to increase the voltage.
Term
 How do we work out electrical power?
Definition
 Power (W)  = Current (Amps) x Voltage
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