Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A level Physics > Unit 2.2 - Resistance > Flashcards

Unit 2.2 - Resistance Flashcards

You may prefer our related Brainscape-certified flashcards:
Physics 101 flashcards AP® Physics flashcards
1
Q

What does the flow of charge allow us to get out?

A

Work

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What do potential differences cause charges to do?

A

Flow from a higher to a lower potential

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Current

A

How quickly charges flow

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Potential difference

A

The difference in energy that a coulomb of charge loses between 2 points

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Unit of potential difference

A

Volt

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What does 1 volt represent?

A

1 Joule per coulomb, so the work done per unit charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Equation involving potential difference

A

W = QV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What does W represent and what’s its unit in W = QV?

A

Work/energy
Joules

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What does Q represent and what’s its unit in W = QV?

A

Charge
Coulomb

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What does V represent and what’s its unit in W = QV?

A

Potential difference
Volts

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What’s the difference between a battery and a cell?

A

Battery - Includes cells
Cell - 1 positive and 1 negative (long and short line)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What does the long line represent in a cell?

A

Positive charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What does the short line represent in a cell?

A

Negative charge

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does a resistor do?

A

Limits/regulates the flow of electrical current in an electric circuit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does a battery do in terms of energy in a circuit?

A

Increases the energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does a resistor do in terms of energy in a circuit?

A

Releases energy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What does a steeper “height” mean in terms of potential energy?

A

Bigger potential energy difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What does a higher potential difference mean in terms of current?

A

Higher current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Why does a higher potential difference lead to a higher current?

A

More kinetic energy is delivered per unit charge to overcome resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What does closing a switch do in terms of potential difference?

A

Brings up the ‘dips’
No potential difference

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

How can we make a circuit have no potential difference?

A

Close the switch

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

What does resistance do and to what?

A

Slows down a current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

What is Ohm’s law?

A

The ratio of the potential difference to the current is constant if the temperature, pressure, material, e.t.c remain constant

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Equation involving resistance

A

R = V/I

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What’s the unit of resistance?

A

Ohms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Worded equation involving resistance

A

Resistance = Potential difference/current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What do we mean when we say “Ohmic behaviour”?

A

That the resistance remains the same

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What do we mean when we say “Ohmic behaviour”?

A

That the resistance remains the same

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

In a potential difference, what type of energy is it transferred from and to?

A

Electrical to other forms

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What would a non-linear part of an I-V graph represent?

A

Hooke’s Law being disobeyed due to the temperature of the wire increasing

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

Describe exactly what resistance IS

A

-when a current flows through a metal, the free electrons drift in 1 direction
-as the electrons travel through the conductor, they will collide with the positive metal ions in the lattice positions
-these collisions cause electrical resistance, as some of the electrons kinetic energy is lost to the ion during the collision
-this causes the vibrational energy of the ion to increase and the temperature of the metal to increase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What determines the resistance of a conductor?

A

The frequency of the collisions between electron and the metal ions

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What does a higher drift velocity mean in terms of resistance and why?

A

Higher drift velocity = electrons collide with ions more times each second and therefore lose more kinetic energy = higher resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What would be the difference between the current-voltage graph of a metal wire and the filament of a lamp?

A

metal wire - straight line through the origin
filament of a lamp - curved

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

Why would the metal wire produce a straight line on a current-voltage graph?

A

resistance (V/I) is constant as temperature is constant throughout

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
36
Q

Why would the filament of a lamp produce a curved line on a current-voltage graph?

A

initially, resistance (V/I) is constant as temperature is constant
then, temperature increases, so resistance increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Which factors effect the resistance of a wire?

A

Temperature
Length
Cross-sectional area
Material

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Derive the equation for power in electrical circuits

A

Equation for potential difference
V = W/Q

Equation for current
I = Q/t

Multiplied together
V x I = W/G x Q/t = W/t (q’s cancel out)
W unit = J
t unit = s
(Power = energy transferred per second, so it works)

P = IV

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
39
Q

Worded equation for power in an electrical ciruit

A

Power (W) = current (A) x potential difference (V)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
40
Q

Equations for power in an electrical circuit

A

P = IV = I^2R = V^2/R

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
41
Q

Why is V^2/R a valid equation for calculating the power of an electrical circuit?

A

P = IV
And I = V/R
Combined =
P = V^2/R

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
42
Q

Why is I^2R a valid equation for cal cutting the power of an electrical circuit?

A

P = IV
V = IR
Combined =
P = I^2R

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
43
Q

What do all metals do to electricity?

A

Conduct it

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
44
Q

Is resistance unique to a metal?

A

Yes

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
45
Q

Which property is resistance related to?

A

Resistivity

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
46
Q

What’s the only property that can change the resistivity of a material?

A

Temperature

47
Q

Resistivity

A

The property of a material related to its resistance
It’s equivalent to the resistance in 1m of a wire of a certain material with a cross-sectional area of 1m^2

48
Q

What is the resistivity of a material constant for?

A

At a specific temperature

49
Q

Resistivity equation

A

R = ρl
—
A

50
Q

What does ρ represent in the equation R = ρl
—
A?

A

Resistivity

51
Q

What does R represent in the equation R = ρl
—
A?

A

Resistance

52
Q

What does l represent in the equation R = ρl
—
A?

A

Length

53
Q

What does A represent in the equation R = ρl
—
A?

A

Cross-sectional area

54
Q

Unit of Resistivity + explanation

A

Ωm

Ohm x metre^2
———————. = ohm x metre
Metre

55
Q

Resistance unit

A

Ω

56
Q

What is Resistivity increased by?

A

Even small amounts of impurity

57
Q

What could alloys have in terms of resistivity?

A

Far greater resistivity than any of its constituents

58
Q

Alloy example

A

Constantan

59
Q

If ρ and A are constant, what happens to R and l?

A

They’re directly proportional, so doubling one doubles the other

60
Q

What happens to many metals at certain temperatures?

A

They become superconducting

61
Q

Superconductivity

A

Where the electrical resistance of a material falls to zero

62
Q

What has to be done to a wire for its resistance to be zero?

A

Has to be cooled to a low enough temperature

63
Q

Superconducting transition temperature symbol

A

TT (imagine the second T is small)

64
Q

Superconducting transition temperature

A

The temperature at which a material becomes a superconductor and has zero resistance

65
Q

What is the superconductivity transition temperature typically very close to for most metals?

A

Absolute zero (0K)

66
Q

If the superconducting transition temperature of a material is above 196°C, what can be done and why?

A

Liquid nitrogen can be used to cool the material down enough for superconducting

67
Q

If a superconducting transition temperature is above WHICH temperature can liquid nitrogen be used to cool the material enough for superconducting?

A

196°C

68
Q

What’s the significance of 196°C?

A

The boiling point of nitrogen

69
Q

What can be used to cool down a material and keep it below its superconducting transition temperature?

A

Liquid nitrogen

70
Q

What is liquid nitrogen used to do?

A

Keep a cool down a material and keep it below its superconductivity transition temperature

71
Q

When is reaching superconductivity transition temperatures useful?

A

Where very high currents are required —> without superconducting wires, very high currents will cause too much power to be dissipated as heat due to the resistance in the wire

72
Q

What would happen without superconducting wires where very high currents are required?

A

Very high currents will cause too much power to be dissipated as heat due to the resistance in the wire

73
Q

Draw and label a graph comparing a non-superconducting metal and a superconductor

A

(See notes)

74
Q

What can superconducting materials resist?

A

A magnetic field from their interiors

75
Q

What does a magnet moving around a conductor usually cause and how is this different in a superconductor?

A

A magnet moving around a conductor induces a current to flow in the conductor - this is the basis of an electrical generator
However, in a superconductor, the induced current exactly opposes the magnetic field causing it, which repels the magnet = strong diamagnetism (“The Meissen effect”)

76
Q

What’s the basis of an electrical generator?

A

A magnet moving around a conductor inducing a current to flow in the conductor

77
Q

What’s the name for, in a superconductor, when an induced current (caused by a magnet moving around a conductor) exactly opposes a magnetic field causing it and repels the magnet?

A

Strong diamagnetism (“The Meissen effect”)

78
Q

Strong diamagnetism (“The Meisser effect”)

A

In a superconductor, the induced current from a magnet moving around a conductor exactly opposes the magnetic field causing it, which repels the magnet

79
Q

How strong is strong diamagnetism?

A

So strong that a magnet can be made to levitate above a piece of superconducting material

80
Q

What allows a magnet to be made to levitate above a piece of superconducting material?

A

Strong diamagnetism (“The Meisser effect”)

81
Q

What was a significant discovery made with a ceramic in terms of superconductivity?

A

A ceramic was discovered to superconduct at 30K (ceramics aren’t usually conductors!)

82
Q

What was the superconductivity transition temperature that was first discovered to be higher than nitrogen’s?

A

92K, whilst Nitrogen’s is 77K

83
Q

What’s good about using liquid nitrogen?

A

Cheap and easily found

84
Q

What’s the record for the highest superconductivity transition temperature?

A

138K

85
Q

Does the entire wire have to be kept under the transition temperature to maintain superconductivity?

A

No - superconductivity can be maintained even if only parts of the superconductor are kept below the transition temperature - the rest can be at room temperature

86
Q

What’s a useful fact related to how superconductivity can be maintained?

A

Only parts of the superconducting wire have to be cooled below the transition temperature to maintain superconductivity - the rest can be at room temperature

87
Q

Give 5 uses for superconductors

A

MagLev trains
Electricity production
Particle accelerators
Magnetic resonance imaging (MRI)
Electric motors

88
Q

How do MagLev trains work?

A

Cause magnetic levitation, as superconductors more or less eliminate friction between the train and the track

89
Q

What was so good about MagLev trains and why was this possible?

A

The lack of friction between the train and the track enabled the train to be able to reach record breaking speeds

90
Q

Which use of superconductors has factors against it and why?

A

MagLev trains
Political and environmental factors due to them having biological effect such as affecting the migration paths of animals

91
Q

Why are superconductors used in energy production?

A

Generators from superconducting wires are much more efficient than copper

92
Q

Why are superconductors used in electricity storage?

A

Once a current is flowing in a superconductor, it doesn’t lose energy, so it can be stored until its needed

93
Q

What happens once a current is slowing in a superconductor?

A

It doesn’t lose energy, so it can be stored until its needed

94
Q

What does MRI stand for?

A

Magnetic Resonance Imaging

95
Q

What does MRI allow doctors to do?

A

Look into the body without cutting flesh

96
Q

How does MRI work?

A

Strong magnetic field from superconductors into the body
Hydrogen atoms within molecules gain energy
Released
Displayed graphically

97
Q

How do superconductors work in particle accelerators? Why are these important?

A

Superconducting magnetic accelerate protons to a speed nearly that of light - could lead to a theory that explains everything

98
Q

How can superconductors be used in electric motors?

A

Superconducting motors are much more efficient than usual motors

99
Q

What would all of our uses of superconductors usually require? Why?

A

Very high currents to produce strong magnetic fields

100
Q

What’s the issue with using ordinary wires at high currents as opposed to superconducting ones?

A

Heating effects of such high currents would melt the wires and would effect the sensitive measuring equipment used

101
Q

In which region of the resistance-temperature graph is a potential difference of 0V required to maintain a current?

A

The whole flat line where the resistance is zero

102
Q

What does it mean if there’s no resistance in terms of electrons?

A

There’s NO collisions between electrons and ions

103
Q

Is V=IR a statement of Ohm’s law? Explain

A

It is, as potential difference is directly proportional to the current, so long as it’s stated that the resistance is constant

104
Q

What temperature do we estimate as room temperature?

A

290K

105
Q

Describe what resistance is in terms of electrons

A

When a current flows through a metal, the free electrons drift in one direction
As the electrons travel through the conductor, they will collide with the positive metal ions in their lattice positions
These collisions cause electrical resistance, as some of the electrons kinetic energy is lost to the ion during the collision
This causes the vibrations, energy of the ion to increase and the temperature of the metal to increase
At higher temperatures, the electrons collide more times each second with the ions, which lowers the drift velocity, therefore lowering the current

106
Q

If p and l are constant, what happens to R and A?

A

They’re inversely proportional - doubling A halves R

107
Q

What happens to the resistance of a wire if the diameter increases?

A

Remember that R and A are inversely proportional, and A= pi x (d/2)^2
So, doubling d will increase the area by 2^2= 4
Sp, R decreases by a factor of 4

108
Q

Ohm’s law definition

A

The potential difference across a conductor is directly proportional to the current through the conductor at constant temperature

109
Q

What is power?

A

Rate of energy transfer

110
Q

What is rate of energy transfer?

A

Power

111
Q

Define resistance

A

The ratio of potential difference to current

112
Q

Describe the resistance of a conductor that obeys Ohm’s law

A

Constant

113
Q

What do batteries do to charges?

A

Give them electrical potential energy

114
Q

Can we always use the potential difference dividing up method?

A

only if the values for resistance are constant

A level Physics (29 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions