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Flashcards in P2 Electricity Deck (36)
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1

What is the National grid?

The National Grid is used to distribute electricity around the country from power stations to consumers. It is the network of pylons and wires you see high above you across the country.

2

Current is a measurement of.......

........how quickly electrical charge flows.

3

A step-up transformer steps the voltage up from 20,000 V to 400,000 V. If the current going in is 25,000 A, what is the output current?

1,250 A. The power stays the same so voltage x current going in = voltage x current going out. The voltage has gone up by a factor of 20, so current goes down by a factor of 20.

4

Explain why transformers are used in the National Grid.

Transformers allow the power to stay high because a high voltage means the current can be lowered. This stops the wire getting warm and losing energy to the surroundings. The voltage is then stepped down for consumers

5

What is AC/DC apart from an Australian rock band?

AC = Alternating Current / DC = Direct current

6

What is the voltage and frequency of the mains?

In the UK, the frequency of mains electricity is 50 hertz. The voltage of mains electricity supplied to UK homes is 230 V.

7

What current flows through a resistor of 40 ohms when connected to a power supply of 12 volts?

I = V/R = 12/40 = 0.3 Amps

8

What is the name and job of the blue wire?

The neutral wire. Stays at zero Volts

9

How would you calculate power?

power = current x voltage

10

What is the rule for voltage in series circuits?

The voltage from a battery is shared between all the components in a series circuit.

11

What is the rule for current in series circuits?

The current has only one route in a series circuit and all ammeters would show identical current.

12

How does the length of a wire affect its resistance?

As the length increases the resistance also increases.

13

Why does an increase in temperature in a wire increase its resistance?

As a metal heats up their resistance increases because their positive metal ions vibrate more and so block the flow of electrons.

14

List the steps (in terms of transformers) from the National Grid from your home or school

Electricity from a power station goes to a step-up transformer to produce high voltage, low current (to prevent energy loss which occurs at high current). Step down transformers are used to produce low voltage for consumers (i.e. your home, school, supermarket)

15

What is the difference between direct current (d.c.), and alternating current (a.c.)?

Direct current (d.c.) is an electric current that always flows in one direction. Alternating current (a.c.) is an electric current that is constantly changing direction.

16

Resistance is........

..a measure of how much a conductor prevents the flow of electrons.

17

The voltage of a battery or cell is a measure of .......

....the energy given to the electrons so that they can flow around the circuit.

18

How would you calculate electrical energy?

electrical energy = power x time

19

Why do some metals have a high resistance?

Some metals have a high resistance because their positive metal ions are larger and block the flow of electrons.

20

What is the equation to find charge?

Charge = current x time Q = It

21

What is the name and job of the green and yellow wire?

The earth wire is a safety wire that is needed to earth appliances with a metal case. This makes it safer to touch the appliance if it develops a fault.

22

What is the name and job of the brown wire?

The live wire carries a current that alternates between a negative and positive voltage.

23

Which has a higher resistance a thick or thin wire?

A thin wire has a higher resistance.

24

Why are the wires are made of copper?

Copper is a good electrical conductor.

25

What is meant by a step-up and step-down transformer?

Step-up transformers increase voltage and step-down transformer decrease voltage

26

What is a transformer?

A transformer is a device to change voltage in a circuit.

27

Current is measured in.....

.......Amps (short for Amperes).

28

Electrical charge is measured in.....

Coulombs

29

What is the name and job of the blue wire?

The neutral wire completes the circuit. It is kept at a zero voltage by the electricity company.

30

What is the rule for current in parallel circuits?

The current is shared between all the components in a parallel circuit because there are different routes that the current can take .