Brainscape's Knowledge GenomeTM

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


See full index

AQA A Level Physics > 3.7 Fields and their consequences > Flashcards

3.7 Fields and their consequences Flashcards

1
Q

What is a force field?

A

An area in which an object experiences a non-contact force

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

How can a force field be represented?

A
  • A vector, describing the direction of the force that would be exerted on the object, which allows the direction of the field to be deduced
  • Field lines, where the distance between the field lines represents the strength of the force exerted by the field in that region
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How are force fields formed?

A

During the interaction of masses, static charge or moving charges

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

How are gravitational fields formed?

A

During the interaction of masses

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

How are electric fields formed?

A

During the interaction of charges

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

What are the similarities between gravitational and electrostatic forces?

A
  • Both follow an inverse square law
  • Both use field lines to be represented
  • Both have equipotential surfaces
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What are the differences between gravitational and electrostatic forces?

A
  • In gravitational fields, the force exerted is always attractive, while in electric fields the force can be either repulsive or attractive
  • Electrostatic forces act on charges, while gravitational forces acts on masses
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What is gravity?

A

The universal attractive force acting between all matter

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

What is Newton’s law of gravitation?

A

The magnitude of force between two masses is directly proportional to the product of the masses, and inversely proportional to the square of the distance between them

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

Describe a uniform gravitational field.

A
  • Equally spaced parallel lines, with arrows pointing towards the surface
  • The same gravitational force is exterted on a mass everywhere in the field
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe a radial gravitational field.

A
  • Equally spaced lines with arrows pointing towards the centre of the object
  • Force exerted depends on position of object in field - as an object moves further away from the centre, the magnitude of the force decreases, as the distance between field lines increases
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is gravitational field strength?

A

The force per unit mass exerted by a gravitational field on an object

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

What is the difference between the gravitational field strength of a uniform field and a radial field?

A

It is constant in a uniform field, but varies in a radial field

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

What is the gravitational potential at a point?

A

The work done per unit mass required to move an object from infinity to a given point

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

What is the gravitational potential at infinity?

A

Zero

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

Why is gravitational potential always negative?

A

The gravitational potential at infinity is zero, and as an object moves from infinity to a point, energy is released as the gravitational potential energy is reduced, and the gravitational force is always attractive, so the system is always doing the work

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

What is gravitational potential difference?

A

The energy per unit mass needed to move an object between two points

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

What are equipotential surfaces?

A

Points of equal potential joined together, so the potential on the surface is constant everywhere

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

What is the gravitational potential difference when moving along an equipotential surface?

A

Zero, so no work is done

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

What is the relationship between gravitational potential and the distance between two objects?

A

The gravitational potential is inversely proportional to the distance between the centres of the two objects

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

What is the gradient of a V-r graph?

A

-g

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

What is Kepler’s 3rd law?

A

The square of the orbital period is directly proportional to the cube of the radius, T²/r³=k

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

How do you derive Kepler’s 3rd law?

A

Centripetal force = gravitational force to find v^2
v^2 = (2πr/T)^2 to find T^2 = (constant) r^3

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

What is the total energy of an orbiting satellite made up of?

A

Kinetic and potential energy

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

Why is the total energy of an orbiting satellite always constant?

A

If the height is decreased, its gravitational potential energy decreases, but it will travel at a higher speed, so kinetic energy increases, so total energy is always kept constant

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

What is escape velocity?

A
  • The minimum velocity an object must travel at in order to escape the gravitational field at the surface of a mass
  • The velocity at which the object’s kinetic energy is equal to the magnitude of its gravitational energy
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What are synchronous orbits?

A

Where the orbital period of the satellite is equal to the rotational period of the object it is orbiting (24 hours if orbiting Earth)

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

What are geostationary satellites?

A

Satellites that follow a specific geosynchronous orbit, their orbital period is 24 hours so they always stay above the same point on Earth, as they orbit directly above the equator

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

What are geostationary satellites used for?

A

Sending TV and telephone signals

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

What are low-orbit satellites?

A

Satellites that have lower orbits than geostationary satellites, so they travel much faster making their orbital periods much smaller

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

What are low-orbit satellites used for and why?

A
  • Monitoring weather
  • Making scientific observations about unreachable locations
  • Military applications, spying
  • They require less powerful transmitters and are able to orbit across the entire Earth’s surface
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

What is Coulomb’s law?

A

The magnitude of the force between two point charges in a vacuum is directly proportional to the product of their charges, and inversely proportional to the square of the distance between them

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

What is air treated as when using the force between two charges equation?

A

A vacuum

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

For a charged sphere, where is charge assumed to act?

A

At the centre of the sphere

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

What is the nature of the force if charges have the same sign?

A

Repulsive

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

What is the nature of the force if charges have different signs?

A

Attractive

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

Compare the magnitude of gravitational and electrostatic forces between subatomic particles.

A

The magnitude of electrostatic forces between subatomic particles is magnitudes greater than the magnitude of gravitational forces, because the masses of subatomic particles are incredibly small, whereas their charges are much larger

38
Q

What is electric field strength?

A

The force per unit charge experienced by an object in an electric field

39
Q

What is the general equation to find electric field strength?

A

E=F/Q

40
Q

Derive the equation ΔW=QΔV.

A

W=Fd
F=EQ
E=ΔV/d, d=ΔV/E
W=(EQ)(ΔV/E), W=QΔV

41
Q

What does the equation ΔW=QΔV represent?

A

The work done by moving a charged particle between the parallel plates of a uniform electric field

42
Q

Describe the trajectory of a moving charged particle entering a uniform electric field initially at right angles.

A

The charged particle will experience a constant electric force either in or opposite to the direction of the field (depending on its charge), causing it to accelerate, so it follows a parabolic shape

43
Q

What is absolute electric potential?

A

The potential energy per unit charge of a positive charge at a point in the electric field

44
Q

Where is the absolute magnitude of electric potential greatest?

A

The surface of a charge

45
Q

What is the electric potential at infinity?

A

Zero

46
Q

What does the value of electric potential being positive or negative depend on?

A

The sign of the charge

47
Q

What is the nature of the electric potential and charge if the charge is positive?

A

Electric potential is positive, and the charge is repulsive

48
Q

What is the nature of the electric potential and charge if the charge is negative?

A

Electric potential is negative, and the charge is attractive

49
Q

On a V-r graph, if V is initially positive, what is the nature of the force?

A

Repulsive

50
Q

On a V-r graph, if V is initially negative, what is the nature of the force?

A

Attractive

51
Q

What does the gradient of a V-r graph represent?

A

The value of electric field strength at that point

52
Q

What is electric potential difference?

A

The energy needed to move a unit charge between two points

53
Q

What does the area under an E-r graph represent?

A

Electric potential difference

54
Q

What is capacitance?

A

The charge stored by a capacitor per unit potential difference

55
Q

What is a capacitor?

A

An electric component which stores charge

56
Q

What does a capacitor consist of?

A

Two conducting parallel plates with a gap between which may be separated by a dielectric (insulating material)

57
Q

What happens when a capacitor is connected to a source of power?

A

Opposite charges build up on the two parallel plates causing a uniform electric field to be formed

58
Q

What is permittivity?

A

A measure of the ability to store an electric field in a material, a property of dielectrics

59
Q

How do you find relative permittivity?

A

By finding the ratio of the permittivity of the dielectric to the permittivity of free space, εr= ε/ε0

60
Q

What is relative permittivity?

A

The dielectric constant of a dielectric, used to calculate the capacitance of a capacitor

61
Q

What is a dielectric formed of?

A

Polar molecules

62
Q

What are polar molecules?

A

Molecules with one end which is positive and one which is negative

63
Q

How are polar molecules arranged when there is no electric field?

A

In random directions

64
Q

What happens to polar molecules when an electric field is present in a capacitor?

A
  • They move and align themselves with the field, with the negative ends rotated towards the positive plate of the capacitor and the positive ends to the negative plate
  • Each molecule now has its own electric field, which now oppose the field formed by the capacitor, reducing this field
65
Q

What does the electric field strength of a polar molecule depend on?

A

The dielectric’s permittivity

66
Q

What happens as a result of polar molecules reducing the electric field formed by the capacitor?

A

The electric field strength decreases, decreasing the potential difference required to charge the capacitor, causing capacitance to increase, as C=Q/V

67
Q

What does the area under a graph of charge against potential difference (Q-V graph) represent?

A

The electrical energy stored by a capacitor

68
Q

What does a Q-V graph of a capacitor look like?

A

A straight line through the origin, as potential difference is directly proportional to charge

69
Q

Describe a circuit in which you can charge a capacitor and take relevant measurements.

A

A series circuit with a power supply, ammeter, resistor and a capacitor, with a voltmeter in parallel with the capacitor

70
Q

What does the area under an I-t graph represent?

A

Charge

71
Q

What does the gradient of a Q-t graph represent?

A

Current

72
Q

Describe what happens in a capacitor once it has been connected to a power supply.

A
  • Current starts to flow and negative charge builds up on the plate connected to the negative terminal
  • On the opposite plate, electrons are repelled by the negative charge building up on the initial plate, so these electrons move to the positive terminal
  • An equal but opposite charge is formed on each plate, creating a potential difference
  • As the charge across the plates increases, the potential difference increases but the electron flow decreases due to the force of electrostatic repulsion also increasing, so current decreases and eventually reaches zero
73
Q

How do you discharge a capacitor?

A

It must be connected to a closed circuit with just a resistor

74
Q

Describe the I-t graph of a charging capacitor.

A

Negative exponential curve, with current tending to zero

75
Q

Describe the V-t graph of a charging capacitor.

A

Positive exponential curve, with potential difference tending to V0

76
Q

Describe the Q-t graph of a charging capacitor.

A

Positive exponential curve, with charge tending to Q0

77
Q

Describe the I-t graph of a discharging capacitor.

A

Negative exponential curve, with current tending to zero

78
Q

Describe the V-t graph of a discharging capacitor.

A

Negative exponential curve, with potential difference tending to zero

79
Q

Describe the Q-t graph of a discharging capacitor.

A

Negative exponential curve, with charge tending to zero

80
Q

What happens when a capacitor is discharged?

A

Current flows in the opposite direction, and the current, charge and potential difference across the capacitor will fall exponentially, so it will take the same time for the values to halve

81
Q

What is the equation involving current for a charging capacitor?

A

I = I0e^-t/RC

82
Q

What is the equation involving current for a discharging capacitor?

A

I = I0e^-t/RC

83
Q

What is the equation involving potential difference for a charging capacitor?

A

V = V0(1 - e^-t/RC)

84
Q

What is the equation involving potential difference for a discharging capacitor?

A

V = V0e^-t/RC

85
Q

What is the equation involving charge for a charging capacitor?

A

Q = Q0(1 - e^-t/RC)

86
Q

What is the equation involving charge for a discharging capacitor?

A

Q = Q0e^-t/RC

87
Q

What is I0?

A

The initial current

88
Q

What is V0?

A

The initial potential difference

89
Q

What is Q0?

A

The initial charge

90
Q

What is the time constant?

A
  • The product of resistance and capacitance, RC
  • The value of time taken to discharge a capacitor to 1/e of its initial value of Q, I or V
  • The value of time taken to charge a capacitor to (1 - 1/e) of its initial value of Q or V
91
Q

What is the gradient of a graph of ln(Q) against t?

A

-1/RC

92
Q

What is the time to halve, T1/2?

A
  • The time taken for the current, charge or potential difference of a capacitor to discharge to half of the initial value
  • T1/2 = -ln0.5RC = 0.69RC

AQA A Level Physics (16 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2025 Bold Learning Solutions. Terms and Conditions