electricity and circuits

Question 1

equation for power in terms of forces

Answer 1

power = work done/ time

Question 2

unit for power

Answer 2

watt / joule per second

Question 3

conventional current

Answer 3

current that flows from positive to negative

Question 4

insulator

Answer 4

holds the electrons tightly to atoms so the electric currents cannot flow

Question 5

conductor

Answer 5

substances which allow electrons to pass through it

Question 6

coulomb

Answer 6

unit of charge

Question 7

rules for a series circuit

Answer 7

• the current stays the same
• has no loops or branches

Question 8

voltmeter

Answer 8

measures the amount of energy per electron

Question 9

potential difference = …

Answer 9

voltage

Question 10

the bigger the voltage, the bigger the …

Answer 10

current

Question 11

doubling the resistance … the current

Answer 11

halves

Question 12

light dependant resistor

Answer 12

(LDR) the resistance decreases as light intensity increases

Question 13

thermistor

Answer 13

resistance decreases as temperature increases

Question 14

diode

Answer 14

• the resistance of the diode is very high then decreases suddenly at a threshold voltage
• diodes only let current flow in one direction and only once the voltage has reached a threshold

Question 15

why can electrons flow more easily through a smaller resistance

Answer 15

there are less forceful collisions with the ions in the wire, possibly due to shorter, wider or different metals

Question 16

uses of diodes

Answer 16

• stops currents from flowing in the wrong direction to prevent damages, e.g. remote batteries
• diodes can be used to convert alternating current from mains electricity to direct current in a phone charger

Question 17

equation for energy in terms of electric circuits

Answer 17

energy = voltage x current x time

Question 18

how to reduce resistance in a circuit

Answer 18

• use low resistance metals such as copper
• make the wire thicker
• cool the wire so ions vibrate less

Question 19

calculation for power using resistance

Answer 19

P = I^2 x R

Question 20

alternating circuit

Answer 20

electricity that is generated when an electromagnet is rotated inside the coil of a machine called an alternator

Question 21

live wire

Answer 21

230v connected to generator at power station. can be fatal if touched

Question 22

neutral wire

Answer 22

return path of the power station to complete the circuit. should be 0v

Question 23

earth wire

Answer 23

connected to the ground with a metal spike for safety. should be 0 volts

Question 24

fuse

Answer 24

• limits the current in the live wire for safety
• too much current would heat up the wire and may cause fires

Question 25

fault current

Answer 25

current that passes through the body

Question 26

earthing

Answer 26

connecting the case to the earth to avoid human injury

Question 27

MCB

Answer 27

• miniature circuit breaker
• disconnects the live wire when the current is too strong

Question 28

what wire is the neutral wire connected to

Answer 28

the earth wire at the substation so electric current can feed return via the earth if there is no fault

Question 29

RCD

Answer 29

• remote current decidual
• switches off electricity automatically if there is a fault

Question 30

equation for charge

Answer 30

Q = IT

Question 31

equation for power (electricity)

Answer 31

P = E/T

Question 32

equation for energy (electricity)

Answer 32

E = QV

Question 33

equation for voltage (resistance)

Answer 33

V = IR

Question 34

state the relationship between current in a total circuit and total resistance

Answer 34

I=V/R
current is inversely proportional to resistance

Question 35

explain why voltage varies with current in a bulb

Answer 35

• as voltage increases, current increases
• electrons flow more quickly and collide with metal ions
• they transfer more energy as they vibrate faster
• as temperature increases, resistance increases, so voltage increases more rapidly

Question 36

explain how the LDR changes current in a circuit

Answer 36

• resistance decreases as light intensity increases
• current increases

Question 37

explain why a 20A fuse is not suitable for an 8.7A plug

Answer 37

• realistic fuse amp should be around 13A so it does not melt in normal use
• 20A is too large, would not protect the cable as the cable would over heat and start a fire before the 20A fuse melts and cuts of the current

Question 38

explain how the fuse works with the earth wire to prevent the user from being electrocuted

Answer 38

• if live wire touches metal casing, a large current would flow through the person to earth, causing electrocution
• if casing is earthed, a large current would flow from the live wire via the case to earth
• the fault current would blow a fuse in the live wire, disconnecting it, making it safe

Question 39

on which wire, (earth, live, neutral), should the switch be connected to

Answer 39

• the live wire
• when switched off, the kettle has no high voltage and is safe