paper 2 physics electricity

Question 1

how should a plug be wired?

Answer 1

each wire is connected to the right pin &firmly screwed in
no bare wires are showing inside the plug
the cable grip is tightly fastened over the cable outer layer

Question 2

what are the metal parts in plugs made from and why?

Answer 2

copper and brass-good conductors

Question 3

what are the 3 wires in a plug and colours?

Answer 3

1) live wire-brown- alternates between high +ve and -ve voltage of about 230v
2) neutral wire- blue-always at 0v
3) earth wire- green and yellow with fuse work together for safety

Question 4

what can earthed conductor never become?

Answer 4

live

Question 5

what is double insulation?

Answer 5

the appliance has a plastic casing and no metal parts showing

Question 6

why don’t you need an earth wire with double insulation?

Answer 6

because plastic insulates the appliance and stops a current flowing through so can’t get a shock- just need live and neutral

Question 7

how does a fuse work?

Answer 7

a fault develops in which the live touched the metal case- which is earthed, so a big current flows in through the live, through the case and out through the earth wire.
this serge in current melt the fuse which cuts off the live supply
this isolates the whole appliance making it impossible to get an electric shock- prevents risk of fire caused by the heating effect of a large current

Question 8

how do residual current circuit breakers work?

Answer 8

usually same current flows through live and neutral, if somebody touches the live wire, a small but deadly current flows through them to the earth. so the neutral wire carries less current than the live wire the RCCB detects this difference in current and cuts off the power by opening a switch

Question 9

how do circuit breakers work?

Answer 9

when they detect a surge in current they break the circuit by opening a switch

Question 10

what are the advantages of circuit breakers over fuses?

Answer 10

they can be easily reset by flicking a switch-fuse doesn’t have to be replaced
they can detect even small current changes that might not be large enough to melt a fuse- more effective at protecting against electrocution

Question 11

what happens when an electric current passes through a resistor?

Answer 11

it gets hot as there is an energy transfer

Question 12

what does the heating effect do to the resistance and current?

Answer 12

it increases the resistor’s resistance so less curren will flow

Question 13

what is electrical power?

Answer 13

the rate at which an appliance transfers energy

Question 14

an appliance with a high power rating does what?

Answer 14

transfers a lot of energy in a short time

Question 15

a high power rating draws what from the supply?

Answer 15

a large current

Question 16

electrical power (W)=

Answer 16

current x voltage

Question 17

energy transferred=

Answer 17

current x voltage x time

Question 18

what is current?

Answer 18

the rate of flow of charge round the circuit-only flow through a component if there’s a voltage across it

Question 19

what is voltage?

Answer 19

the driving force that pushes the current round. it’s the energy of the electrons. it’s the potential difference

Question 20

if you increase voltage?

Answer 20

more current will flow

Question 21

increase resistance?

Answer 21

less current will flow

Question 22

voltage=

Answer 22

current x resistance

Question 23

the gradient for v-i graphs is?

Answer 23

1/R

Question 24

describe metal filament lamp graph

Answer 24

as temp of metal filament increases the resistance increases so a curve

Question 25

describe a wire graph

Answer 25

the current through a wire is proportional to voltage so linear

Question 26

describe graph for resistors

Answer 26

the current though a resistor is proportional to voltage- diff resistors have diff resistances so different slopes

Question 27

describe diode graph

Answer 27

current will only flow in one direction- goes along x and curves up

Question 28

what are LEDs?

Answer 28

light-emitting diodes - emit light when a current flows through them in forward direction - used on digital clocks, traffic lights, remote controls - used in appliances to show they are switched on

Question 29

what are LDRs?

Answer 29

light-dependent resistors- changes its resistance depending on the light that falls on it - in bright light-resistance falls - in darkness -resistance is highest - good for burglar detectors

Question 30

what are thermistors?

Answer 30

temperature-dependent resistors - in hot conditions, resistance drops - in cool conditions- resistance goes up - useful as car engine temperature sensors

Question 31

what happens in series circuit?

Answer 31

current stays constant voltage decreases as you go round circuit resistance combine

Question 32

what happens in parallel circuits?

Answer 32

current splits voltage stays constant resistors combine= 1/Rtotal= 1/R1+1/R2 etc

Question 33

in solid metal conductors what is charge carried by?

Answer 33

negatively charged electrons

Question 34

charge=

Answer 34

current x time

Question 35

2 metals that conduct?

Answer 35

copper and silver- a current can flow through them

Question 36

2 insulators?

Answer 36

plastic and rubber- current can't flow through them

Question 37

What happens when a charge drops through a voltage?

Answer 37

It transfers energy

Question 38

Where is energy supplied to the charge?

Answer 38

At the power source to 'raise' it through a voltage

Question 39

When does the charge give up this energy?

Answer 39

When it 'falls' through any voltage drop in components elsewhere in the circuit

Question 40

When is more energy transferred?

Answer 40

The bigger the change in voltage, the more energy is transferred for a given amount of charge passing through the circuit

Question 41

What is the voltage?

Answer 41

The energy transferred per unit charge passed

Question 42

What is one volt defined as?

Answer 42

One joule per coulomb

Question 43

What is build-up of static caused by?

Answer 43

Friction

Question 44

What happens when two insulating materials are rubbed together?

Answer 44

Electrons are scraped off one and put on the other, this leaves a positive electrostatic charge on one and a negative electrostatic charge on the other

Question 45

What do electrically charged objects attract?

Answer 45

Small objects placed near them

Question 46

What happens when a polythene rod is rubbed with a cloth duster?

Answer 46

Electrons move from the duster to the rod. The rod becomes negatively charged and duster is left with an equal positive charge

Question 47

What happens when an acetate rod is rubbed with a cloth duster?

Answer 47

Electrons move from the rod to the duster. The duster becomes negatively barged and the rod is left with an equal positive charge

Question 48

What is a positive static charge caused by?

Answer 48

Electrons moving

Question 49

How can a charged conductor be discharged safely?

Answer 49

By connecting it to earth with a metal strap. The electrons flow down the strap to the ground if the charge is negative and flow up the strap from the ground if the charge is positive

Question 50

When a charge builds up, what else does?

Answer 50

The voltage causing sparks

Question 51

The greater the charge on an isolated object, the greater the what between it and the what?

Answer 51

The greater the voltage between it and the earth. If the voltage gets big enough there's a spark which jumps across the gap

Question 52

What's the gold-lead electroscope experiment demonstrating electrostatic charge?

Answer 52

1- a gold- leaf electroscope has a metal disc connected to a metal rod, at the bottom of which are attached two thin pieces of gold leaf 2- put the electroscope in a glass beaker with a plug made of an insulator 3- when a rod with a known charge is brought near to the disc of the electroscope, electrons will either be attracted to or be repelled from the metal disc- depending on the charge of the rod 4- this induces a charge in the metal disc, which in then induces a charge in the gold leaves 5- both gold leaves will have the same charge, so will repel each other, causing them to rise 6- when the rod is taken away, the gold leaves will discharge and fall again

Question 53

What is the experiment demonstrating electrostatic charge suspending a charged rod?

Answer 53

1- suspend a rod with a known charge on a thread and see if there is repulsion or attraction when the rod you're testing is brought close to it 2- if there is an attraction, then the test row has the opposite charge to the suspended rod 3- if there is a repulsion, then the test rod has the same charge as the suspended rod

Question 54

How are van de Graff generator used to demonstrate electrostatic charge?

Answer 54

1- it's made up of a rubber belt moving round plastic rollers underneath a metal dome 2- an electrostatic charge is built up on the metal done as the belt goes round 3- if you stand on an insulated chair and place your hands on the dome, electrons will move between your body and the dome, giving your body a charge 4- the human body conducts charge and like charges repel so the charges will spread out as much as possible throughout the body. The charge is strong enough to make your hairs repel each other and stand on end

Question 55

How does an inkjet printer work?

Answer 55

1- tiny droplets of ink are forced out of a fine nozzle making them electrically charged 2- the droplets are deflected as they pass between two metal plates. A voltage is applied to the plates- one negative and the other positive 3- the droplets are attracted to the plate of the opposite charge and repelled from the plate with the same charge 4- the size and direction on the voltage across each plate changes so each droplet is deflected to hit a different place on the paper 5- loads of tiny dots make the printout

Question 56

How does a photocopier work?

Answer 56

1- the image plate is positively charged. An image of what you're copying is projected onto it 2- whiter bits of what's being copied make light fall on the plate and the charge leaks away in those places 3- the charged bits attract negatively charged black powder which is transferred into positively charged paper 4- the paper is heated so the powder sticks

Question 57

How does clothing crackle?

Answer 57

When synthetic clothes are dragged over each other (tumble dryer or over your head) electrons get scraped off, leaving static charges on both parts leading to an attraction and sparks as the charges rearrange themselves

Question 58

How does lightening happen?

Answer 58

Rain drops and I've bump together inside storm clouds, knocking off electrons and leaving the top of the cloud positively charged and the bottom of the cloud negative. This creates a huge voltage and a big spark causing thunder and a big sound

Question 59

Why is fuel- filling dangerous?

Answer 59

1- as fuel flows out of a filter pipe, static can build up 2- this can lead to a spark and in dusty or fumy places 3- the solution is to make the nozzles out of metal so the charge is conducted away, instead of building up 4- it's also good to have earthing straps between the fuel tank and the fuel pipe

Question 60

Describe a method a student could use to obtain a good set of data from a circuit to produce a graph from

Answer 60

1- start with the resistance of the variable resistor fixed at a high level 2- then take a reading of current from the ammeter and voltage from the voltmeter 3- decrease the resistance of the variable resistor in equal steps and take another pair of readings each time 4- make sure you take several pairs of readings and plot on a v-I graph