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electricity Flashcards

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1
Q

reason why increasing resistance may not affect voltage

A

voltmeter may not be sensitive enough

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2
Q

steel increases

A

mechanical strength cables

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3
Q

why superconducting wire increase efficiency

A

no resistance no power loss

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4
Q

state and explain what happens to brightness of lamp if connected to power supply w/ internal resistance(2)

A
  • lamp less bright

- power now wasted

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5
Q

application superconductor and why (2)

A

MRI / strong magnetic field

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6
Q

application superconductor and why (2)

A

MRI / strong magnetic field

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7
Q

application superconductor and why (2)

A

transformer - no energy dissipation

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8
Q

what’s a superconductor and how does it become a superconductor (3)

A

superconductivity means a material has zero resistivity/resistance (1)
resistivity decreases with temperature or idea of cooling (1)
becomes superconducting when you reach the critical/certain/
transition temperature (1)

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9
Q

what happens to resistance of cable when embedded filaments are made superconducting (3)

A 
the resistance decreases (to zero) (1)
copper still has resistance (1)
but this is in parallel with filaments (which have zero resistance) (1)
hence total resistance is zero (1)
current goes through filaments (1)
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10
Q

explain why resistance NTC decreases as temp rises (2)

A
  • increased temp = release electrons

- current increases as charge carrier density increases

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11
Q

2 heating element at 230V 500W connected to 230V supply in series + parallel
explain why only one will give power output 1KW(6)

A

parallell

  • lower resistance = higher current = more power
  • parallel voltage across each constant whereas in series split between the 2
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12
Q

in potential divider questions ALWAYS

A

give p.d. affect on all resistors / components

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13
Q

to say __ of parallel branch say

A

resistance in parallel combination decreases

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14
Q

what give largest resistance

A

series

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15
Q

define emf

A

emf is the work done / energy transferred by a voltage source / battery / cell ✓per unit charge✓

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16
Q

explain why voltage on graph always less than emf - why difference voltage emf becomes larger w/ increasing current

A

-internal resistance
-terminal pd = emf - lost volts
-lost volts increase as current increases
-

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17
Q

if gives 2 requirements for something to work and asks if it works

A

state both

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18
Q

why voltmeter has a high resistance

A

so current is 0

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19
Q

remember 2 cells =

A

double emf

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20
Q

1 reason for rechargeable battery to have low internal resistance

A

charges quicker as less energy wasted

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21
Q

define emf

A

joules per coulomb (of charge)/work done per unit charge

where charge moved (whole way) round circuit

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22
Q

lost volts

A

emf - terminal pd

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23
Q

2 points for why voltage measured less than emf

A
  • work done in battery due to internal resistance

- lost volts

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24
Q

why would ammeter reading be greater if motor in series is lifting a load

A

battery has to provide more energy / power

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25
Q

why something will not start with higher internal resistance e

A

terminal pd will not be high enough

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26
Q

when talking about effect of switch always say

A

when switch closed CURRENT FLOWS then rest

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27
Q

asks how values obtained from internal resistance practical

A

by altering variable resistor

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28
Q

what two statements to say when voltmeter < emf

A
  • current through battery
  • pd lost across internal resistance
  • work done to lose pd
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29
Q

why does pd between two points in circuit not change even if cell replaced w/ cell of internal resistance (2)

A
  • terminal pd decreases

- BUT ratio of resistors remain constant OR voltmeter not sensitive enough to measure change

30
Q

potential divider equation

A

combination resistors in series connected to voltage source

31
Q

3 points to make in potential divider 3 marker about pd across each component (3)

A
  • change in resistance one = pd change
  • pd across component + pd other = supply pd (in series)
  • so change in pd on other component
32
Q

never give fractional ! always

A

decimals

33
Q

2 marker potential divider question

A
  • resistance (__) decrease = pd decrease

- so greater (PROPORTION/SHARE) PD to (_)

34
Q

2 marker on why pd wouldn’t change if resistance of different parallel branch changed

A 
no change (1)
constant pd across parallel branches (1)
35
Q

define 1 volt

A

1 joule per couloumb charge

36
Q

advantage to high value resistance in potential divider circuit

A

reduced current

37
Q

compare potential divider in controlling current across resistor to variable resistor circuit (2)

A
  • potential divider = sensitive control current

- variable resistor = larger current but not near 0A

38
Q

why resistance NTC decreases w/ temp increases (3)

A
  • more charge carriers available
  • internal energy used to liberate electrons
  • more significant than vibrations lattice ions
39
Q

for power and resistance equation

A

V squared / R

40
Q

why does resistance of thermistor decrease as temperature rises (3)

A

-extra charge carriers released as temperature rises
-increased thermal agitation of atoms resists flow of
charge carriers
- 1st effect overwhelms 2nd

41
Q

brightness of lamps w/ same current

A

same

42
Q

advantage and disadvantage to potential divider method of Current (2)

A
  • adv- better control 0- to max

- disadvan-power wasted lower half resistor always carries

43
Q

adv and disas to rehostat method

A

-adv- easier to connect

disad- minimum current through bulb never 0

44
Q

temp measured at

A

voltmeter

45
Q

3 points for how voltmeter reading across LDR changes as light increases - DIFFERENT AS ACROSS LDR

A

LDR resistance drops
voltmeter reading decreases
because more conduction electrons/charge
carriers released

46
Q

why resistance LDR decreases at higher temp (2)

A
  • more charge carriers released - liberated electrons

- increases current

47
Q

application superconductor and reason

A
  • maglev trains / MRI - strong magnet

- no thermal energy produced

48
Q

how to get readings for reverse bias

A

reverse cell

49
Q

why non ohmic

A

resistance not constant

50
Q

when asked how results obtained always say ( and in 6 markers)

A

variable resistor

51
Q

for filament lamp 4 marker say

A

current heats filament

same in reverse direction / mirror image

52
Q

practical use diode

A

protect against current surges

53
Q

ohms law definition

A

VI directly proportional if temp constant

54
Q

on emf graph questions - for value internal resistance

A

say modulus gradient is r

55
Q

when pd across component is 0 say

A

no current flows

56
Q

component placed in parallel between two components of equal pd =

A

0V as diff between two components NOT SAME

57
Q

is bulb filament breaks

A

ignore from circuit

58
Q

energy transformed across battery

A

from EMF

59
Q

energy dissipate across battery

A

internal r

60
Q

in describe filament IV curve for increasing temp say

A

increasing RATE of collisions

61
Q

graph relationship power and current

A

P=I^2R therefore y=x^2 graph

62
Q

on VI graph for resistance NEVER

A

find gradient tangent for point - only ever read off points

63
Q

if voltmeter put in branch in series w/ resistor in parallel circuit current through that branch is

A

0A as voltmeter infinite resistance - therefore discard any resistance in that branch as no current flows through it

64
Q

when a resistor in added in circuit - 2 marker explain as to why

A

increase resistance
therefore limit max current
therefore prevent cell from overheating ( current too high) = short circuit

65
Q

if given gradient min and grad max how to find grad

A

mean

66
Q

why would 2 cells in series go out faster than 2 cells in parallel

A
  • 2 cells in parallel receive double the amount of energy per second
  • more charge per second passes through cells in series
67
Q

what would happen If use battery with much higher internal resistance to start car

A
  • wouldn’t start

- lower terminal pd

68
Q

if light intensity 450 W m-2 with 0.15 efficiency use

A

450 x 0.15

69
Q

how to take measurements emf and V

A

Voltmeter connected across cell terminals ✓
Switch open, voltmeter records ε
Switch closed, voltmeter records V

70
Q

for potential divider never divide PD it’s

A

SPLITTING OF PD

physics specific vocabulary (15 decks)

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