2 - electricity

Question 1

what is electrical current

Answer 1

• the flow of electrical charge
• can only flow round a closed circuit if there is potential difference
• in a single loop the current is the same everywhere

Question 2

what is potential difference

Answer 2

• the force that pushes charge around

Question 3

what is resistance

Answer 3

• anything that slows the flow down

Question 4

ammeter

Answer 4

• measure CURRENT flowing through test wire
• SERIES circuit

Question 5

voltmeter

Answer 5

• meaures the PD flowing through test wire
• must be in a PARALLEL circuit

Question 6

investigating factors affecting resistance practical

Answer 6

1. attach crocodile clip to wire - level to 0cm on ruler
2. attach 2nd crocodile clip to 10 cm
3. close switch and measure the current and pd
4. open and move 2nd clip to 20cm and close and record again
5. repeat
6. plot on graph and use the pd and current to work out resistance and then put it against length of wire

Question 7

LRD in bright and dark light and uses

Answer 7

• dependent on the intensity of light
• bright lights —> resistance falls
• darkness —> resistance is highest
• can be used in burglar alarms

Question 8

thermistor in hot and cold places and uses

Answer 8

• dependent on the tmperature
• hot —> resistance drops
• cold —> resistance rises
• can be used as thermostats

Question 9

series circuits

Answer 9

• if you remove one component - everything will stop
• current is the same everywhere I1 = I2 = I3
• the potential difference is shared Total = R1 + R2 + R3..,
• the total resistance is the sum of the componants

Question 10

parallel circuits

Answer 10

• if you remove one thing it wont effect the other components
• all componants have a full source of pd V1 = V2 = V3
• current is shared Itotal = I1 + I2 + I3 …

Question 11

what happens if you add a resistor to a parallel circuit

Answer 11

• reduces the total resistance

Question 12

ohmic conductor graph

Answer 12

current is directly proportional to the potential difference at a constant temp
- straight line through the graph
- i on the y axis
- v on the x axis

Question 13

filament lamp graph

Answer 13

as the current increases the temp of lamp increases so the resistance increases because the particles vibrate more and therefore collide more with the current
- curved graph

Question 14

diode graph

Answer 14

current only flows in one direction and then the current suddenly increase - like a plank of wood snapping
graph starts flat and then increases

Question 15

I-v characteristics

Answer 15

• ohmic conductor
• filament lamp
• diode

Question 16

sensing circuits

Answer 16

used to turn on or increase the power to certain components in a circuit depending on the conditions that the circuit is operating in.

Question 17

ac

Answer 17

• alternating pd used creates an alternating current - fluctuates between positive and negative
• this means direction that charge is flowing is constantly flowing back and forth

Question 18

dc

Answer 18

• produced by a direct potential difference
• either positive or negative the whole time
• so charge is always flowing in the same direction
• found in cells/ batteries eg phone or caluclator

Question 19

live wire

Answer 19

• brown
• provides the alternating potential dofference from the mian supply
• 230 V

Question 20

neutral wire

Answer 20

• blue
• completes the circuit by being covered in blue pastic
• 0V

Question 21

earth wire

Answer 21

• yellow and green
• provides a low resistance path to the ground. In the event of a fault, the live current passing through the case will follow this path to the ground instead of passing through a person.
• 0V

Question 22

how do you get an electric shock

Answer 22

• your body is at 0V
• if you touch LIVE wire a potential differnece is prduced across your body
• and then current flows through you - electric shock

Question 23

whats the National grid

Answer 23

• giant system of cables and transformers
• transfers electrical power from power stations anywhere on the grid to anywhere its needed

Question 24

what pd and current does the national grid use

Answer 24

• really high pd
• really low current (if current is too high then the thermal energy will be lost into surroundings)

Question 25

transformers

Answer 25

have a primary and secondary coil joined with an iron core

Question 26

step up and step down transformers

Answer 26

step up -> increases pd = more turns in secondary coil step down -> reduces pd = more turns in primary

Question 27

how does friction cause static

Answer 27

- when insulating materials are rubbed - neg charged electrons are scraped off one and onto the other - makes the materials electrically charged with a positive static charge on one and an equal negative static charge on the other - ONLY ELECTRONS MOVE

Question 28

how is a spark caused

Answer 28

- as electric charge builds up the PD increases between earth object 0v and charged object - high PD causes a strong electrical field - this causes air particles to be removed - then when current flows - SPARK

Question 29

UK AC mains supply - pd and frequency

Answer 29

230 V 50 HZ - therefore the pd and current fluctuate between +230v and -230v, 50 times per second