Brainscape's Knowledge GenomeTM

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


See full index

A-Level Physics > 7: Fields & Their Consequences > Flashcards

7: Fields & Their Consequences Flashcards

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

Concept of a Force Field

A

Region in which a body experiences a non-contact force

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

Force fields arise from ____

A

The interaction of mass, of static charge and between moving charges

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

Similarities & Differences between Gravitational & Electrostatic Forces (1:4, 1:1)

A
  • Similarities:
    • Both have inverse-square laws
    • Use field lines
    • Use of potential concept
    • Equipotential surfaces
  • Differences:
    • Masses always attract, but charges may attract or repel
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

Gravity

A

Universal attractive force between all matter

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

Magnitude of Force between Two Point Masses

A

F = G m₁ m₂ / r² where G is the gravitational constant

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

g

A

Force per unit mass as defined by g = F / m

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

Magnitude of g in Radial Field

A

g = G M / r²

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

Representation of Gravitational Field by Gravitational Field Lines

A

https://qph.fs.quoracdn.net/main-qimg-1e788e321185dc777fa96ced46727c30

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

Gravitational Potential

A

The work that needs to be done to move a unit mass from infinity to the point

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

The gravitational potential at an ____ from the mass will be ____

A

Infinite distance, zero

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

Gravitational Potential Difference

A

The energy needed to move a unit mass between two points with different gravitational potentials

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

Work Done in Moving Mass m

A

ΔW = m ΔV

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

Gravitational Equipotential Surfaces

A

They contain all the points with the same gravitational potential

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

No ____ when moving along ____

A

Work is done, an equipotential surface

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

V in Radial Field

A

V = - GM / r

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

Significance of Negative Sign in Gravitational Potential

A

Gravitational potential is 0 at ∞ so work needs to be done against the field to reach ∞

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

Graphical Representation of Variation of g with r

A

https://www.a-levelphysicstutor.com/images/fields/g-graph01.jpg

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

Graphical Representation of Variation of V with r

A

https://www.cyberphysics.co.uk/Q&A/KS5/gravitation/q5a.png

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

Relation of V & g

A

g = - ΔV / Δr

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

Area Under a Graph of g against r

A

ΔV

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

Orbital period and speed related to ____

A

Radius of circular orbit

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

Derivation of T² ∝ r³ (5)

A
  • Force between two masses: F = G m₁ m₂ / r²
  • Centripetal force: F = m₂ v² / r
  • m₂ v² / r = G m₁ m₂ / r²
    ⇒ v = √(G m₁ / r)
  • v = 2 π r / T (distance / time)
  • 2 π r / T = √(G m₁ / r)
    ⇒ T² / 4 π² r² = r / G m₁
    ⇒ T² = (4 π² / G m₁) r³
    ∴ T² ∝ r³
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Escape Velocity

A

The minimum speed an object needs to leave a gravitational field and not fall back due to gravitational attraction

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

Escape Velocity Formula (3)

A
  • Kinetic energy lost = Gravitational potential energy gained
  • ½ m v² = G M m / r
  • v = √(2 G M / r)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Energy Considerations for an Orbiting Satellite (3)

A
  • An orbiting satellite has kinetic and potential energy – its total energy is always constant
  • In a circular orbit, orbital speed and distance above the mass are constant so kinetic and potential energy are both constant
  • In an elliptical orbit, a satellite will speed up as its orbital radius decreases so kinetic energy increases as potential energy decreases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Synchronous Orbit

A

When an orbiting object has an orbital period equal to the rotational period of the object it is orbiting

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

Geostationary Orbit (4)

A
  • Geostationary satellites are always above the same point on Earth
  • Their orbit is in the plane of the equator
  • Their orbital period is the same as Earth’s rotational period (synchronous orbit and same angular speed)
  • Given their orbital period is 24 hours, orbital radius can be calculated as ~42 000 km
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

Low Orbits (3)

A
  • Low orbiting satellites are cheaper to launch and require less powerful transmitters so they’re useful for communications
  • Imaging satellites have low orbits for imaging and monitoring weather
  • As the planet and the satellite rotate at different angular speeds, the satellite doesn’t stay over the same point on Earth so it can cover the whole of the surface
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Force between Point Charges in a Vacuum

A

F = (1 / 4 π ε₀) ((Q₁ Q₂) / r²)

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

Permittivity of Free Space

A

ε₀ is the opposition offered against the formation of an electric field in a vacuum

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

Comparison of Magnitude of Gravitational and Electrostatic Forces between Subatomic Particles

A

The distance between the particles is small, but the mass of the particles is also small so gravitational forces are small whereas electrostatic forces are big

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

Representation of Electric Fields by Electric Field Lines (2)

A

Uniform field: https://th.bing.com/th/id/OIP.cgxeo3AL1zJpHRVbgAeLzQHaFj
Radial field: https://i.ytimg.com/vi/c8H1j9LWjls/maxresdefault.jpg

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

Electric Field Strength

A

Force per unit charge

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

E

A

Force per unit charge defined by E = F / Q

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

Magnitude of E in a Uniform Field

A

E = V / d

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

Derivation from Work Done Moving Charge between Plates (3)

A
  • E = F / Q and E = ΔV / d
  • F / Q = ΔV / d
  • F d = Q ΔV
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
37
Q

Trajectory of Moving Charged Particle Entering a Uniform Electric Field Initially at Right Angles (3)

A
  • A charged particle feels a constant force parallel to the electric field lines
  • If it is positively / negatively charged, the force is the same / opposite direction to the field lines
  • This causes the particle to accelerate at right angles to its original motion so it follows a parabolic path
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
38
Q

Magnitude of E in Radial Field

A

E = (1 / 4 π ε₀) (Q / r²)

39
Q

Absolute Electric Potential

A

The electric potential energy that a unit positive charge would have at that point in an electric field

40
Q

Absolute Electric Potential is Zero ____

A

At an infinite distance from the charge creating the field

41
Q

Electric Potential Difference

A

The energy needed to move a unit positive charge between two points in an electric field

42
Q

Work Done in Moving Charge Q

A

ΔW = Q ΔV

43
Q

Electric Equipotential Surfaces

A

They contain all the points with the same absolute electric potential

44
Q

No ____ Moving Charge along an ____

A

Work is done, equipotential surface

45
Q

Magnitude of Electric V in a Radial Field

A

V = (1 / 4 π ε₀) (Q / r)

46
Q

Graphical Representation of Variation of E with r

A

https://entrancecorner.s3.amazonaws.com/media/uploads/2018/06/10/3321-a.PNG

47
Q

Graphical Representation of Variation of E & V with r

A

https://www.shaalaa.com/images/_4:4e26160e991b4d31bc8a40237a4a8441.png

48
Q

V Related to E

A

E = ΔV / Δr

49
Q

ΔV is Area under Graph of ____

A

E against r

50
Q

Definition of Capacitance

A

C = Q / V

51
Q

Dielectric Action in a Capacitor

A

C = A ε₀ εᵣ / d

52
Q

Relative Permittivity & Dielectric Constant

A

The ratio of the permittivity of a material to the permittivity of free space

53
Q

Polar Molecules (2, 1:2)

A
  • A dielectric is made up of lots of polar molecules (with a positive and negative end)
  • When no charge is stored by a capacitor, no electric field is generated, so the molecules are aligned randomly
  • When charge is applied to the plates of a capacitor, an electric field is generated between them:
    • The negative ends of the molecules are attracted to the positively charged plate, and vice versa
    • This causes the molecules to rotate and align themselves anti-parallel to the electric field generated between the plates
54
Q

Area under Graph of Charge against PD

A

Energy stored

55
Q

Capacitor Energy Stored Equation

A

E = 1/2 Q V = 1/2 C V² = 1/2 Q² / V

56
Q

Graphs of Q, V, I against Time for Charging

A

https://www.scienceandmathsrevision.co.uk/wp-content/uploads/2019/05/cap-discharge_2-1024x339.jpg

57
Q

Graphs of Q, V, I against Time for Discharging

A

https://www.scienceandmathsrevision.co.uk/wp-content/uploads/2019/05/cap-discharge_3-1024x339.jpg

58
Q

Capacitor Discharge Equations

A

Q = Q₀ e^(-t / (R C)), V = V₀ e^(-t / (R C)), I = I₀ e^(-t / (R C))

59
Q

Capacitor Charge Equations

A

Q = Q₀(1 - e^(-t / (R C))), V = V₀(1 - e^(-t / (R C))), I = I₀ e^(-t / (R C))

60
Q

Time Constant

A

R C

61
Q

Time to Halve

A

T_(1/2) = 0.69 R C

62
Q

Force on a Current-Carrying Wire in a Magnetic Field

A

F = B I l when field is perpendicular to current

63
Q

Fleming’s Left-Hand Rule (3)

A
  • The first finger points in the direction of the uniform magnetic field
  • The second finger points in the direction of conventional current
  • The thumb points in the direction of the force
64
Q

Magnetic Flux Density

A

B, the force on one metre of wire carrying a current of one amp at right angles to the magnetic field

65
Q

Tesla

A

One tesla is the magnetic flux density that produces a force of one newton in a wire with length one metre with one amp

66
Q

Required Practical 9

A

Investigation of the charge and discharge of capacitors

67
Q

Required Practical 9: Charging Method (3)

A

https://www.inchcalculator.com/wp-content/uploads/2019/02/resistor-capacitor-circuit.png
1. Fully discharge the capacitor by connecting its two ends with a wire
2. Ensuring that it is broken, set up the circuit as shown in the diagram, connecting a data logger in parallel with the capacitor
3. Set the data logger to recording voltage, record the resistance of the resistor and complete the circuit

68
Q

Required Practical 9: Discharging Method (3)

A

https://www.inchcalculator.com/wp-content/uploads/2019/02/resistor-capacitor-circuit.png
1. Charge the capacitor using a 6V battery
2. Ensuring it is broken, set up the circuit as shown in the diagram, connecting a data logger in parallel with the capacitor
3. Set the data logger to recording voltage, record the resitance of the resistor and complete the circuit

69
Q

Required Practical 10

A

Investigate how the force on a wire varies with flux density, current and length of wire using a top pan balance

70
Q

Required Practical 10 Method (4)

A

https://media.sciencephoto.com/image/c0021045/800wm/C0021045-Conductor_in_magnetic_field_experiment.jpg
1. Set up the apparatus as shown in the diagram with a variable resistor in series with the multimeter
2. Zero the balance, which the cradle is resting on
3. Turn on the power supply and record the reading on the balance and current
4. Repeat step 3, adjusting the variable resistor, number of magnets on the cradle or length of the wire in the cradle

71
Q

Newton’s Law of Gravitation

A

The force of attraction between two point-masses is proportional to the product of the masses and inversely proportional to square of distance between them

72
Q

Force on Charged Particles Moving in Magnetic Field

A

F = B Q v when the field is perpendicular to velocity

73
Q

Direction of Force on Positive & Negative Charged Particles

A

To use Fleming’s left-hand rule for charged particles, use you middle finger as the direction of motion of a positive charge. If the particle carries a negative charge, point your finger the other way

74
Q

Circular Path of Particles (5)

A
  • By Fleming’s left-hand rule, the force on a moving charge travelling perpendicular to a magnetic field is always perpendicular to its direction of travel
  • This satisfies the condition for circular motion
  • Force due to magnetic field, F = B Q v, and centripetal force, F = m v² / r
  • Radius of circular motion, r = m v / B Q, and frequency of rotation, f = B Q / (2 π m)
  • So, increasing a particle’s velocity means its circular path has a larger radius, but it takes the same time to complete the path
75
Q

Cyclotron (5)

A
  • Cyclotrons are used to produce radioactive tracers or high-energy beams of radiation
  • A cyclotron is made up of two hollow semi-circular electrodes with a uniform magnetic field applied perpendicular to the plane of the electrodes and an alternating pd applied between the electrodes
  • Textbook Page 335
  • Particles follow a semi-circular path in an electrode then, when they leave the electrode, they are accelerated in the gap. In the other electrode, their circular path has a greater radius as they are faster. When they leave this electrode, the pd has been reversed, repeating the process and causing the particles to spiral outwards increasingly fast before exiting the cyclotron
  • Since the frequency of the motion doesn’t depend on radius, the particle spends the same amount of time in each electrode so the alternating pd has a fixed frequency
76
Q

Magnetic Flux

A

Φ = B A where B is normal to A

77
Q

Flux Linkage at an Angle (3)

A
  • https://www.jobilize.com/ocw/mirror/col12074/m58477/CNX_UPhysics_30_03_FChanges.jpg
  • The component of the magnetic field perpendicular to the area of the coil is B cos θ
  • So, flux linkage, N Φ = B A N cos θ
78
Q

Faraday’s Law

A

Induced emf is directly proportional to the rate of change of flux linkage

79
Q

Magnitude of Induced EMF =

A

Rate of change of flux linkage

80
Q

Magnitude of Induced EMF Equation

A

ε = N ΔΦ / Δt

81
Q

Straight Conductor Moving in a Magnetic Field (4)

A
  • Textbook Page 344
  • Lenz’s law says that the induced emf will produce a force that opposes the motion of the conductor
  • Fleming’s left-hand rule can be used to find the direction of the emf
  • If the conductor has length l and moves with constant velocity v:
    ε = N ΔΦ / Δt
    = B ΔA / Δt
    = B l Δd / Δt
    = B l v
82
Q

Electromagnetic Induction (3)

A
  • If there is a relative motion between a conductor and magnetic field, the electrons in the conductor will experience a force and accumulate at one end
  • This induces an emf across the rod
  • If the rod is part of a complete circuit, a current will be induced
83
Q

EMF Induced in a Coil Rotating Uniformly in a Magnetic Field

A

ε = B A N ω sin ω t

84
Q

Alternating Currents & Voltages

A

Currents and voltages that vary sinusoidally with time

85
Q

Root Mean Square Current & Voltage

A

The average current and voltage from an alternating power supply is the root mean square - dividing the peak value by √2

86
Q

Alternating Current Equations

A

Iᵣₘₛ = I₀ / √2
Vᵣₘₛ = V₀ / √2

87
Q

Peak-to-Peak Current & Voltage

A

Double the peak current / voltage or the distance between the peak and trough on the waveform

88
Q

Mains Electricity Root Mean Square Voltage

A

230 V

89
Q

Transformer Equation

A

Nₛ / Nₚ = Vₛ / Vₚ

90
Q

Transformer Efficiency Equation

A

Iₛ Vₛ / (Iₚ Vₚ)

91
Q

Eddy Currents (4)

A
  • Eddy currents are looping currents induced by the changing magnetic flux in the core
  • They create a field that acts against the field that induced them, reducing its strength
  • They also dissipate energy by generating heat
  • These effects can be reduced by having layers of the core separated by thin layers of insulator so a current can’t flow
92
Q

Causes of Inefficiencies in a Transformer (3)

A
  • Heat is generated by resistance in the coils. To reduce this, wires with low resistance can be used
  • Energy is needed to magnetise the core and this is wasted as it heats the core. A magnetically soft material, that magnetises easily, should be used
  • The coils should be as close as possible to increase the amount of magnetic flux (created by the primary coil) cut by the secondary coil
93
Q

Transmission of Electrical Power at a High Voltage

A

Electrical power is transmitted at a high voltage, in the national grid, to produce a low current in the power lines so the power dissipated is reduced

A-Level Physics (9 decks)

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