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Physics - Paper 1 > Topic 7 - Electric and Magnetic Fields > Flashcards

Topic 7 - Electric and Magnetic Fields Flashcards

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1
Q

What is a force field?

A

A region in which a non-contact force is experienced by a corresponding interacting particle

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2
Q

What is an electric field?

A

A region in which a charged particle will experience a non-contact force

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3
Q

What is electric field strength?

A

The force per unit charge experienced by a charged particle when placed at that point in the field

Force per unit charge acting on a small positive charge

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4
Q

State the equation used to calculate the force a charge experiences in an electric field.

A

Force = electric field strength x charge

F = EQ

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5
Q

What law determines the magnitude of the electric force between two charges?

A

Coulomb’s Law

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6
Q

State Coulomb’s law in words.

A

The force between two charges is directly proportional to the product of their charges and inversely proportional to the square of their separation

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7
Q

Give Coulomb’s law in equation form.

A

F = (kQq) / r^2

Where k = 1 / 4πε0

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8
Q

Describe the electric field pattern around a positive point charge.

A

A radial field, acting outwards

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9
Q

Describe the electric field pattern around a negative point charge

A

A radial field, acting inwards

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10
Q

Describe the uniform electric field between parallel plates.

A
  • straight lines of equal spacing
  • from positive to negative
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11
Q

What equation is used to calculate the electric field between parallel plates?

A

E = V/d

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12
Q

What is electric potential?

A

The amount of energy required to move a positive test charge from infinity to a given point in an electric field

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13
Q

How do you calculate electric potential for a radial field?

A

F = kQ / r

Where k = 1 / 4πε0

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14
Q

What are equipotentials?

A

Equipotentials are lines along which the electric potential remains the same

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15
Q

How do you calculate the work done in a moving charge along an equipotential?

A

No work is done when moving a charge along an equipotential since the electric potential doesn’t change

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16
Q

What does a capacitor do?

A

Capacitors are used to store charge in a circuit

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17
Q

What two factors determine how much charge can be stored by a capacitor?

A
  • The potential difference across it
  • The capacitance
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18
Q

What is capacitance?

A

Capacitance is a measure of how much charge can be stored by a capacitor per unit potential difference across it

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19
Q

State the equation used to calculate the capacitance from the charge and potential difference.

A

Capacitance = charge / potential difference

C = Q/V

20
Q

What is the unit of capacitance?

A

CV^-1

F (farad)

21
Q

What is represented by the area under a capacitor’s charge-potential graph?

A

The energy stored by a capacitor

22
Q

What is represented by the gradient of a capacitor’s charge-potential graph?

A

Capacitance

23
Q

Give three equations to calculate the energy stored by a capacitor.

A

W = 1/2 QV
W = 1/2 CV^2
W = (1/2 Q^2) / C

24
Q

Describe a charge-time graph for charging a capacitor. What does the gradient represent?

A
  • positive curve (like top left corner of circle)
  • plateaus off
  • gradient = current
25
Q

Describe a current-time graph for charging a capacitor. What does the area represent?

A
  • negative curve (like bottom left corner of a circle)
  • exponential
  • area = charge
26
Q

Describe a voltage-time graph for charging a capacitor.

A
  • positive curve (like top left corner of a circle)
  • plateaus off
27
Q

What value is given by the product of resistance and capacitance?

A

The time constant of the circuit

28
Q

What does the time constant of a circuit tell you?

A

The time the capacitor will take to reach 63% of its total charge, and the time taken for it to discharge to 37% of its full charge

29
Q

What is a magnetic field?

A

A magnetic field is a region in which a magnetic pole will experience a non-contact force

30
Q

In which direction do magnetic field lines point?

A

From north to south

31
Q

What is magnetic flux density?

A

Magnetic flux density is a measure of the strength of a magnetic field. It can be viewed as the number of magnetic field lines that pass through a given area

32
Q

What three factors determine the force exerted on a charge moving through a magnetic field?

A
  • the magnetic flux density
  • the charge of the particle
  • the velocity of the particle perpendicular to the field
33
Q

State the equation used to calculate the force exerted on a charge moving through a magnetic field.

A

F = Bqvsinθ

34
Q

What is the relationship between the direction of a charge’s motion and the direction of the magnetic force it experiences?

A

The force is always perpendicular to the charge’s motion

35
Q

Describe and explain the path taken by a charge in a magnetic field.

A

The charge will move in a circular path. This is because the magnetic force always acts perpendicular to the charge’s motion and so acts as a centripetal force

36
Q

What is produced by a current-carrying wire?

A

A magnetic field is produced in concentric circles around a wire when a current passes through it

37
Q

What occurs when a current-carrying wire is placed in a magnetic field?

A

The wire will experience a force due to the permanent magnetic field interacting with a the wire’s magnetic field

38
Q

What three factors affect the force experienced by a current-carrying wire placed in a magnetic field?

A
  • the magnetic flux density of the wire
  • the current passing through the wire
  • the length of the wire
39
Q

State the equation used to calculate the force experienced by a current-carrying wire.

A

F = BILsinθ

40
Q

What is Fleming’s left-hand rule used for?

A

To determine the direction of the force experienced by a current-carrying wire or moving charge in a magnetic field

41
Q

What does the thumb represent when using Fleming’s left-hand rule?

A

The thumb represents the direction of the force

42
Q

What does the first finger represent when using Fleming’s left-hand rule?

A

The direction of the field

43
Q

What does the second finger represent when using Fleming’s left-hand rule for a moving charge?

A

The direction that a positive charge would move. This means that if it is a negative charge, you must point your second finger on the opposite direction to its motion

44
Q

What does the second finger represent when using Fleming’s left-hand rule for a current-carrying wire?

A

The direction of conventional current flow

45
Q

What is electromagnetic induction?

A

When a conducting rod moves relative to a magnetic field, the electrons in the rod will experience a force (as they are charged particles), and build up on one side of the rod, causing an emf to be induced in the rod

46
Q

What is Faraday’s law?

A

The magnitude of induced emf is equal/directly proportional to the rate of change of flux linkage

ε = N (ΔΦ) / (Δt)

47
Q

What is Lenz’s law?

A

The induced emf is always in such a direction as to oppose the change/motion that caused it

ε = -d(NΦ) / dt

Physics - Paper 1 (6 decks)

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