EX unit two: electricity

Question 1

what colour is the earth wire

Answer 1

green and yellow

Question 2

what colour is the live wire

Answer 2

red/brown

Question 3

what colour is the neutral wire

Answer 3

blue

Question 4

when wiring a three pin plug, what must the cable insulation be firmly gripped by

Answer 4

the cable anchor

Question 5

all mains wiring is insulated with how many layers of insulation

Answer 5

2

Question 6

why is all mains wiring insulated with 2 layers

Answer 6

it prevents the separate conductors (live, neutral and earth) from touvhing and prevents anyone touching a live (mains voltage) wire.

Question 7

what does it mean when some appliances are double insulated (as well as the wiring)

Answer 7

that the outer casing is made out of an insulating material like plastic

Question 8

why is it useful to double insulate appliances

Answer 8

so that no one gets an electric shock.

Question 9

appliances with a metal outer casing that the user might touch must be…

Answer 9

earthed. the earth wire ensures that the outer casing is held at 0V and provides a very low resistance path for the current in the event of a fault in which the live wire touches the casing. this means the fault current will be very large and cause the fuse to blow immediatly, disconnecting the live supply.

Question 10

what material are cartridge fuses

Answer 10

ceramic

Question 11

what happens to a fuse once it has blown

Answer 11

it has to be replaced

Question 12

what are circuit breakers

Answer 12

they perform the same job as fuses but are usually operated magnetically and may be reset by pressing a button.

Question 13

what are RCCB’s

Answer 13

residual current circuit breakers

Question 14

why do cables that carry electricity around our homes have very low electrical resistance

Answer 14

to make the unwanted conversion of electricity as small as possible.

Question 15

power =

Answer 15

current x voltage

Question 16

what is current measured in

Answer 16

amps (A)

Question 17

what is voltage measured in

Answer 17

volts (V)

Question 18

what is power

Answer 18

the rate at which electrical energy is converted in an appliance.

Question 19

energy =

Answer 19

power x time

Question 20

what is energy measured in

Answer 20

joules (J)

Question 21

what does AC stand for

Answer 21

alternating current

Question 22

what does DC stand for

Answer 22

direct current

Question 23

what is alternating current

Answer 23

an alternating supply, like the mains, causes the current to change continuously, with electricity flowing in one direction then the other.

Question 24

what is direct current

Answer 24

a direct supply, like batteries, makes electricity flow in one direction only.

Question 25

why are metals good conductors of electricity

Answer 25

they have large numbers of de-localised electrons - electrons that aren't bound to any particular atom in the structure of the metal. they are free to move, so when an electric force acts on the electrons it forces them to 'drift' in the direction of this electric force.

Question 26

electric current is

Answer 26

the rate of flow of electric charge through ta conductor

Question 27

what is charge measured in

Answer 27

coulombs (C)

Question 28

current =

Answer 28

charge / time

Question 29

what is the symbol for charge

Answer 29

Q

Question 30

1 volt =

Answer 30

1 joule per couloumb

Question 31

energy =

Answer 31

charge x voltage

Question 32

what measures current

Answer 32

an ammeter

Question 33

what measures voltage

Answer 33

a voltmeter

Question 34

what does an ammeter tell you

Answer 34

how many coulombs of charge are passing through the lamp per second.

Question 35

what does voltage tell you

Answer 35

how many joules of energy are being converted to heat and light per coulomb of charge are passing through the lamp.

Question 36

is an ammeter placed in series or parallel

Answer 36

series

Question 37

is a voltmeter placed in series or parallel

Answer 37

parallel

Question 38

why is the current always the same as it flows through a series circuit

Answer 38

there are no alternative routes for the current to follow instead.

Question 39

why isn't the current always the same as it flows through a parallel circuit

Answer 39

the current can split to take two or more routes.

Question 40

what appliances are wired in parallel

Answer 40

mains sockets outlets, mains lights and decorative lights.

Question 41

in a series circuit, the energy supplied by the cell is _________ between the components so the voltage across each component will _________

Answer 41

shared | vary

Question 42

in a parallel circuit, each component has its own connections to the cell so does not have to ________. the voltage across each branch in the circuit will be the ______.

Answer 42

share | same

Question 43

voltage =

Answer 43

current x resistance

Question 44

what is the symbol for resistance

Answer 44

R

Question 45

what is resistance measured in

Answer 45

ohms

Question 46

give a use for a resistor

Answer 46

simple lamp dimmer circuits or volume control in audio equipment

Question 47

resistors can be varied by

Answer 47

rotary or sliding action

Question 48

what are thermistors made from

Answer 48

semi-conductors

Question 49

thermistor's resistance decreases as...

Answer 49

temperature increases

Question 50

what are LDR's made from

Answer 50

semi-conductors

Question 51

more light shining on an LDR =

Answer 51

less resistance

Question 52

what are LDR's used in

Answer 52

light sensing circuits

Question 53

diodes and LED's only allow an electric current to pass in the direction of...

Answer 53

the arrow. one direction has huge resistance and the other has very little.

Question 54

insulators examples

Answer 54

rubber, glass, and many types of plastic

Question 55

protons are _____ charged

Answer 55

positively

Question 56

neutrons carry no ________ ________

Answer 56

electric charge

Question 57

electrons are ________ charged

Answer 57

negatively

Question 58

the charges on the proton and electron are?

Answer 58

equal in size but of opposite sign

Question 59

all atoms have equal numbers of electrons and protons, so the charges balance out and the atoms are overall,

Answer 59

neutral.

Question 60

unlike charges _______ and like charges ________

Answer 60

attract | repel

Question 61

what happens when you rub two materials together?

Answer 61

some electrons are torn from the surface of one of the materials and transferred to the other. the material which loses electrons now has a net positive charge because there are now more positively charged protons than electrons. the material that gained electrons now has more negatively charged electrons than positively charged protons and is therefore negatively charged

Question 62

uses of static electricity

Answer 62

inkjet printers, photocopiers, paint spraying, electrostatic precipitators.

Question 63

problems with static electricity

Answer 63

electric shocks, fuelling tanks and aircraft, handling microprocessors and computer 'chips'.