Section 2 - Electricity

Question 1

current

Answer 1

rate of flow of charge (carried by electrons) in a circuit
(AMPS - A)

Question 2

voltage

Answer 2

what drives current round circuit (also known as potential difference)
Volts - V

Question 3

resistance

Answer 3

anything that slows flow down
ohm (Ω)

Question 4

ammeter

Answer 4

measures current in amps flowing through a component
- must be placed in series

Question 5

voltmeter

Answer 5

measures voltage (in V) across a component
- must be placed in parallel

Question 6

mains supply

Answer 6

in uk 230v alternating current - so constantly changing direction

Question 7

battery supplt

Answer 7

direct current - always in same direction

Question 8

Voltage formula

Answer 8

V=IR
voltage = current x resistance

Question 9

I-V graph

Answer 9

shows how current varies as you alter the voltage

Question 10

I-V graph working out

Answer 10

gradient = resistance
steeper gradient = low resistance
straight line graph = constant gradient therefore resistance

Question 11

wire i-v graph

Answer 11

/ shape
current through a wire at constant temp is proportional to the voltage

Question 12

different resistors i-v graph

Answer 12

/ varying
current through a resistor at a constant temperature is proportional to voltage.
- different resistors have different resistances therefore slightly different slopes

Question 13

metal filament lamp i-v graph

Answer 13

S kinda shape
as the temperature of the metal filament increases the resistance increases hence the curve

Question 14

diode i-v graph

Answer 14

—l shape

current will only flow through a diode in one direction as shown

Question 15

Light Emitting Diodes

Answer 15

indicate the presence of current in a circuit. (light up when current goes through in forward direction)

Often used by appliances to show that they are switched on and for digital clocks, traffic lights, and remote controls

advantages - no filament that will burn out

Question 16

Light Dependant Resistor

Answer 16

a special type of resistor that alters its resistance depending on how much light falls on it

bright light - resistance falls
darkness - resistance highest

useful for electronic circuits like burglar detectors

Question 17

Thermistor

Answer 17

temperature-dependant resistor

hot - resistance drops
cold - resistance builds

useful temp detectors for car engines, thermostats, and fire alarms

Question 18

series circuits

Answer 18

• different components are connected in a line, end to end, between the +ve and -ve of power supply
• if you remove/disconnect one they all stop working (so impractical in reality)

Question 19

series circuit Characteristics:

Answer 19

• there’s a bigger voltage supply when more cells are in series
• current is the same everywhere
• voltage is distributed between components according to their resistance
• total resistance is sum of resistance in each component

Question 20

parallel circuits

Answer 20

each component is separately connected to +ve and-ve of the supply.
- if you remove or disconnect a component it will hardly affect the others
components on same branch share series rules

Question 21

parallel circuits Characteristics:

Answer 21

• voltage is the same across all branches
• current is shared between branches
• total cuurent is the same as addition of current in separate components
• junctions - current either splits or rejoins (total current going in a junction = total current going out)
• current through a branch depends on resistance in branch

Question 22

charge (C) through a circuit formula

Answer 22

current x time
Q = It

Question 23

charge drps blah blah

Question 24

energy transferred (J)

Answer 24

charge x voltage
E=QxV

or

charge x current x resistance
QxIxR

Question 25

a plug

Answer 25

three wires - live, neutral and earth

(earth only needed in emergencies)

Live wire (brown) - around 230v a.c.
neutral wire (blue) - 0v
electricity flows through both

earth wire (green/yellow) there for safety

Question 26

safety measures in a plug

Answer 26

1) all appliances with metal cases must be “earthed” to reduce the danger of electric shock - an earthed conductor can never become live

2) if the appliance has a plastic casing and no metal parts showing then it is said to be double insulated (if so it doesn’t need an earth wire)

Question 27

how do earth wires and fuses work

Answer 27

• if something happens and live wire accidentally touches a metal case then because it is earthed a big current passes through the live wire, case and earth wire
• surge in current melts the fuse which cuts off the live supply
• this isolates the whole appliance, making it impossible to get an electric shock and prevents risk of fire from heating effect of a large current

Question 28

what are circuit breakers

Answer 28

alternatives to fuse
- break current by opening a switch. the circuit can later easily be reset by flipping the switch (more convenient and cheap than fuses)

Question 29

Residual Current Circuit Breaker

Answer 29

• normally same current goes through live and neutral, but if someone touches live wire then current will flow through them to earth, meaning neutral wire carries less current. The RCCB detects the difference and cuts off power supply by opening a switch

Question 30

Residual Current Circuit Breaker

Answer 30

Residual Current Circuit Breaker advantages

1) safer - quick as it doesnt have to wait for fuse to melt
2) work for small current charges not detected by fuses, so more efffective

Question 31

Resistors

Answer 31

when there is ressistance there is a energy transfer which heats the resistor.
- this happens because electrons collide with ions in lattice that makes up resistor as they flow through it giving the ions energy with causes them to vibrate and heat up
- heating effect increases ressistance so less current can flow (or greater voltage needed for same current)
- heating effect could cause components to melt - causing the circuit to stop working . Fuses use this effect to protect circuits
- heating effect has other advantages - toaster contains coil with really high ressistance and when current passes through temp inreases so much it glows and goved of infrared radiation which cooks the bread

Question 32

electrical power defenitions

Answer 32

electrical power is the rate at which an appliance transfers energy
This energy comes from the current flowing through it so an appliance with a high power rating will draw a large current from the supply

fuese have curent ratings

Question 33

electrical power formula

Answer 33

P = IV
electrical power = current x voltage

Question 34

electrical appliances - energy transferred

Answer 34

energy transfered = current x voltage x time
E=IxVxt