electricity

Question 1

relationship between current through resistor and potential difference

Answer 1

it’s directly proportional, resistance does not increase if current increased.(ohmic conductor) but this is only true when temperature is constant

Question 2

why are resistors used?

Answer 2

to control potential difference in circuits

Question 2

relation between current through filament lamp and potential difference

Answer 2

it is not directly proportional,
- bcs filament gets hot which increases resistance
-bcs atoms in filament vibrate more, electrons in current now collide more with the atoms,
-more energy needed to push current thru fil

Question 3

what is resistance?

Answer 3

anything in circuit opposing flow of current

Question 4

what is the difference between direct and alternating current?

Answer 4

dc current only flows in one direction.
-the flow of ac current is constantly changing. the mains supply for ac is at 230V and 50 Hz per second.

Question 5

why are step up transformers used?

Answer 5

-when elec is transmitted, energy lost thru heating in cables, higher for high current.
-trans elec at high voltage reduces current for the same amount of power,
-so step up transformers are used to increase voltage, decrease current and reduce energy loss

Question 6

explain why electricity is transmitted at a high pd

Answer 6

-to trans high power, either high pd or high current is needed. high current is less efficient as it wastes more energy as thermal from wires heating up. trans at high pd means lower current can be used which reduces energy loss meaning trans more efficient

high power trans= +pd OR +current => +energy loss,,,,, +pd= -current= - energy loss= +efficient

Question 7

why can a large charge on an isolated object result in a spark

Answer 7

-large charge causes large pd betw obj and earth, pd can get large enough for spark to jump betw obj and an earthed conductor

Question 8

explain with ref to elec fields how car gives man electric shock when putting hand near it

Answer 8

-car has a large static charge, pd betw car and earth is large.
-this causes strong electric field, which ionises the air particles around, so air can conduct elec,
-man is an earthed conductor, so spark jumps across gap from car to man

Question 9

what is charge

Answer 9

measure of total current that flowed within a certain period of time

Question 10

In a series circuit, the current is:
In a series circuit, the potential difference of the battery is:

Answer 10

-same everywhere
-shared across components

Question 11

in a parallel circuit, every component has the same …. and shares the ….

Answer 11

-p.d.
-current

Question 12

in a parallel circuit, loops w/ greater resistance, take a ……. …. of current

Answer 12

lower share

Question 13

more components in a parallel circuit…

Answer 13

less total resistance

Question 14

step up transformers increase….. and decrease ….. to minimise …..

Answer 14

-voltage / p.d.
-current
-energy loss

Question 15

the uk mains supply is

Answer 15

230 V and 50 Hz, alternating current

Question 16

state the three wires colours and functions

Answer 16

-live, brown
provides the alternating p.d. (230V)

-blue, neutral
acts by completing the circuit and carries away current, has a p.d. of 0V

-green yellow, earth
stops appliance from becoming live in case live wire touches casing, by providing alternate pathway for current to flow

Question 17

what causes an electric shock

Answer 17

a difference in voltage causes electricity to pass from one to another
humans have a p.d. of 0V so touching live wire will cause a large current to flow through

Question 18

a sudden increase in current is called a

Answer 18

surge
could happen when you turn an appliance on or off
or because of a fault in the appliance
can damage appliance, cause fires, electric shocks

Question 19

how do fuses/ circuit breakers promote safety

Answer 19

-breaks the circuit when current gets too high
-very thin piece of wire that’s connected to live wire
-if there’s surge, huge amount of current will flow through the live wire and fuse
-fuse heats up and melts, breaks circuit

Question 20

benefit and disadvantage of fuses

Answer 20

simple and cheap
but permanently broken after a single surge, have to be replaced each time

Question 21

circuit breakers vs fuse

Answer 21

-CB doesn’t get perm. damaged
-it just gets tripped and turns off circuit
-can be reset
-more expensive than fuses

Question 22

what is double insulation

Answer 22

-appliance is covered in plastic coating
-no exposed metal parts
-plastic doesn’t conduct elec so no shock
-these appliances usually only have live & neutral wire

Question 23

what is static electricity

Answer 23

build up of charge on insulating materials

Question 24

what happens when two materials are rubbed against each other
-in terms of insulating and conducting materials

Answer 24

the electrons form one material rub off to the other material

-in conducting materials the electrons are able to move, so can just flow straight back again, thr4 no charge ever builds up (can but it is very uncommon)

-in insulating materials electrons not able to flow back so one is left with a positive static charge and other with negative static charge

Question 25

in static charges, only the ……. are being transferred

Answer 25

electrons

Question 26

what happens when an object keeps on gaining negative electrons

Answer 26

-size of the charge increases
-p.d build up betw obj and any earthed obj (any object with 0V, such as humans)
-if the p.d is big enough, electrons can jump betw the gap, causing a spark

Question 27

the field lines in a positive and negative particle

Answer 27

-goes into the negative
-comes out of positive

Question 28

what could happen when there is a strongly charged piece of metal surrounded by air

Answer 28

-air is an electrical insulator and doesn’t conduct electricity
-however, strong electrical field, like the one around metal can cause surrounding air particles to lose electrons and form positive ions, (ionisation)
-once air ionised, it can conduct electricity
this is how sparks are able to go betw objs, travelling through the air

Question 29

IV Characteristics practical
-current, p.d vary resistance, temp, switch, graph

Answer 29

• measure the current in R using the ammeter
• measure the p.d. across R using voltmeter
• vary resistance of variable resistor
• record a range of values of current and p.d.
• ensure current low, avoid temp increase
• switch circuit off betw/ readings
• reverse connection of R to power supply
• repeat measurements of I and V in negative direction
• plot a graph of current against p.d.

Question 30

what is the error regarding eye positioning called

Answer 30

Parallax Error

Question 31

strong magnetic fields can ionise…

Answer 31

air around them, causing sparks