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Electromagnetism: Fields Flashcards

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1
Q

What is an electric field?

A

The region that surrounds electrically charged particles where a force is exerted on other electrically charged particles.

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2
Q

What is electric field strength?

A

The electrical force acting on unit positive charge.

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3
Q

Sketch an electric field pattern in a single positive point charge.

A

Hint: Charge = outwards

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4
Q

Sketch an electric field pattern in a single negative point charge.

A

Hint: Charge = inwards

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5
Q

Sketch an electric field pattern in two oppositely charged parallel plates

A

Hint: Parallel, charge towards negative.

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6
Q

Sketch an electric field pattern in a positive and negative point charge.

A

Hint: side to side, energy towards negative.

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7
Q

Sketch an electric field pattern in two identical point charges.

A

Hint: side to side, charges curving away from each other

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8
Q

What is electrical potential at a point?

A

The work done in moving unit positive charge from infinity to that point.

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9
Q

What does any charge given to a conductor always reside on?

A

The outer surface of the conductor

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10
Q

What is a consequence of charge given to a conductor residing on the outer surface?

A

The electric field inside a conductor must be zero.

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11
Q

What is electrostatic shielding?

A

When devices that might be affected by an electric field are enclosed in a conductive material.

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12
Q

What is an example of where electrostatic shielding is used?

A

A Faraday Cage.

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13
Q

Sketch a graph of the electric field around a charged sphere or radius r

A

Hint: straight diagonal line at 0, then vertical line upwards, then long curve down

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14
Q

Sketch a graph of the electrostatic potential around a charged conducting sphere of radius r

A

Hint: Straight line across from top of y axis, then short curve downwards.

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15
Q

Summary of Millikan’s Oil Drop Experiment

A
  • Atomiser used to produce spray of tiny oil droplets
  • Pulled downwards through a small hole by gravity
  • Observing terminal velocity to calculate mass
  • Droplets fell between two plates where electric field was applied
  • Varied voltage in order to balance downwards gravitational force with upwards electrical force.
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16
Q

What is the electronvolt (eV)?

A

A unit of energy, often used in high-energy particle physics.

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17
Q

What is 1eV equal to?

A

1.6 x 10^-19 J (energy of an electron)

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18
Q

What are ferromagnetic materials?

A

Ones which can become permanently magnetised.

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19
Q

What are some examples of ferromagnetic materials?

A

Iron, steel, cobalt, nickel

20
Q

Magnetic field patterns in an isolated bar magnet

A

Travelling outwards from north, into south

21
Q

Magnetic field patterns in two opposite poles adjacent.

A

Travelling outwards from north, into south

22
Q

Magnetic field patterns in two like poles adjacent

A

Two south ends curving away from each other, north still travelling into south

23
Q

What does the relative spacing of the field lines in a magnet indicate?

A

The field’s strength. Closer lines = stronger magnetic field

24
Q

What does the direction of the magnetic field around a current carrying wire depend on?

A

The direction of current flow.

25
Q

Sketch a magnetic field around a solenoid

A

Hint: shape of magnetic field same as that created around a bar magnet.

26
Q

sketch a magnetic field around the earth

A

Hint: geographic north pole = magnetic south pole

27
Q

What is magnetic induction, B?

A

The strength of a magnetic field at a point.

28
Q

Right hand rule for a negative charge:

A

Thumb - direction of motion (force)
First finger - direction of magnetic field (north to south)
Second finger - direction of current flow (i.e electron flow)

29
Q

Summarise charge moving perpendicular to a Magnetic field

A
  • force of magnetic field on charged particle is at right angle to motion.
  • Direction of motion is changed and leads to particle moving in circular path
  • Force always acts towards centre of curvature and causes centripetal acceleration
30
Q

Derive r = mv/qB

A
  • F = mv^2/r, F = qvB
  • qvB = mv^2/r
  • qB = mv / r
  • r = mv/qB
31
Q

Summarise charge moving at an angle to a magnetic field

A
  • Charge will follow helical path moving forward

- two components of the particle’s velocity; perpendicular to magnetic field (vsin0) and parallel to field (vcos0)

32
Q

What is the job of the perpendicular component of the particle’s velocity

A

Creating the circular motion

33
Q

What is the job of the parallel component of the particle’s velocity

A

Creating the pitch in the helilx.

34
Q

What is the pitch of the helix in a magnetic field?

A

The distance between adjacent loops in the helix after one period.

35
Q

What equation is used to find the pitch in a helix?

A

p = vcos0 T

36
Q

What equation is used to find the frequency of the rotation in a helix?

A

f = qB / 2(pi)m

37
Q

What equation is used to find the period of rotation in a helix?

A

T = 2(pi)m / qB

38
Q

Summarise a bubble chamber

A
  • Charged particle leaves track of tiny bubbles due to ionisation
  • Tracks spiral inwards due to loss of energy and velocity
  • particles with opposite charges (eg electron and positron) spiral in opposite directions.
39
Q

What is the force mediating particle of a strong nuclear force?

A

Gluon

40
Q

What is the force mediating particle of a weak nuclear force?

A

W(+-) & Z bosons

41
Q

What is the force mediating particle of an electromagnetic force?

A

Photon

42
Q

What is the force mediating particle of a gravitational force?

A

Graviton

43
Q

What is the equation used to calculate an absolute uncertainty

A

(sqrt) (uncertainty X)^2 + (uncertainty Y)^2 + (uncertainty X=Z)^2

44
Q

At what degrees dose maximum force occur in a current?

A

90 degrees (perpendicular to magnetic field)

45
Q

At what degrees does zero force occur in a current?

A

0 degrees (parallel with magnetic field)

46
Q

What is the equation used to find time taken in a semicircular path?

A

t = sv, s = (pi) r

t = (pi) r / v = (pi) / v, mv/ qB

:. t = (pi) m / qB

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