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physics > 2 - electricity > Flashcards

2 - electricity Flashcards

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1
Q

what is electrical current

A
  • 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
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2
Q

what is potential difference

A
  • the force that pushes charge around
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3
Q

what is resistance

A
  • anything that slows the flow down
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4
Q

ammeter

A
  • measure CURRENT flowing through test wire
  • SERIES circuit
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5
Q

voltmeter

A
  • meaures the PD flowing through test wire
  • must be in a PARALLEL circuit
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6
Q

investigating factors affecting resistance practical

A
  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
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7
Q

LRD in bright and dark light and uses

A
  • dependent on the intensity of light
  • bright lights —> resistance falls
  • darkness —> resistance is highest
  • can be used in burglar alarms
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8
Q

thermistor in hot and cold places and uses

A
  • dependent on the tmperature
  • hot —> resistance drops
  • cold —> resistance rises
  • can be used as thermostats
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9
Q

series circuits

A
  • 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
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10
Q

parallel circuits

A
  • 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 …
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11
Q

what happens if you add a resistor to a parallel circuit

A
  • reduces the total resistance
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12
Q

ohmic conductor graph

A

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

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13
Q

filament lamp graph

A

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

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14
Q

diode graph

A

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

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15
Q

I-v characteristics

A
  • ohmic conductor
  • filament lamp
  • diode
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16
Q

sensing circuits

A

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

17
Q

ac

A
  • 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
18
Q

dc

A
  • 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
19
Q

live wire

A
  • brown
  • provides the alternating potential dofference from the mian supply
  • 230 V
20
Q

neutral wire

A
  • blue
  • completes the circuit by being covered in blue pastic
  • 0V
21
Q

earth wire

A
  • 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
22
Q

how do you get an electric shock

A
  • 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
23
Q

whats the National grid

A
  • giant system of cables and transformers
  • transfers electrical power from power stations anywhere on the grid to anywhere its needed
24
Q

what pd and current does the national grid use

A
  • really high pd
  • really low current (if current is too high then the thermal energy will be lost into surroundings)
25
Q

transformers

A

have a primary and secondary coil joined with an iron core

26
Q

step up and step down transformers

A

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

27
Q

how does friction cause static

A
  • 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
28
Q

how is a spark caused

A
  • 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
29
Q

UK AC mains supply - pd and frequency

A

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

physics (14 decks)

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