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Electromagnetism > Magnetism > Flashcards

Magnetism Flashcards

1
Q

true or false; any breaks in a series circuit ceases the current to flow

A

true

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2
Q

what is the equation for cost of electricity?

A

Cost = Power (kW) * time (hrs)* cost (cents/ kWh)

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3
Q

Define magnetism

A

fundamental property of matter

  • physical property of matter that causes certain materials to experience a force when near other magnets or magnetic fields
  • magnetic materials : Fe, Ni, Co, neodymium
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4
Q

What is a permanent magnet

A

object that displays persistent magnetism

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5
Q

what are the two magnetic regions

A

south and north pole

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6
Q

true or false; magnetic monopoles exist

A

false

- there is no such thing

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7
Q

why don’t magnetic monopoles exist

A

when a magnet is cut in half; poles will re-establish themselves

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8
Q

when do magnets experience a force

A

when around other magnets

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9
Q

what are the fundamental laws of magnetism

A

like poles repel

opposite poles attract

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10
Q

What is a magnetic force

A

mediated by a magnetic field

- surrounds a magnet (just like E-field surrounds a charge)

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11
Q

what is the symbol for magnetic field

A

B

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12
Q

true or false; magnetic field has a magnitude and direction

A

true

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13
Q

Which direction do the arrows (field lines) go

A

north to south pole

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14
Q

What are the units for magnetic fields

A

Tesla (T) = 10 000 Gauss (G)

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15
Q

true or false; north pole is pushed along the field lines

A

true

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16
Q

true or false; south pole is pushed along the field lines

A

false; south pole is pushed against the field lines

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17
Q

true or false; a magnet put in an external magnetic field will attempt to align itself parallel to the field lines

A

true

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18
Q

The Earth is like a big bar magnet. The north pole of a compass needle points towards North (North Canada to be precise). Where is the magnetic south pole of the Earth?

A

North Canada

- because north of a compass is attracted to south pole of the Earth

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19
Q

what causes an electric charge

A

is the lack or excess of elementary electric charges (electrons)

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20
Q

What did Oersted show?

A

that a current flowing through a wire can deflect a compass needle

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21
Q

What was Oersted’s demonstration

A

he placed a magnetic needle beneath a current carrying wire

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22
Q

true or false; an electric current produces a magnetic field

A

true

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23
Q

What is current

A

the flow of electric charge

24
Q

what is the source of all magnetism

A

the movement of electric charge

25
Q

what are the 2 quantum mechanical contributions that describes an electrons movement

A
  • electrons: spin angular momentum

- orbitals: orbital angular momentum

26
Q

what are electrons

A

fermions

27
Q

describe the characteristics of an electrons

A
  • no two electrons have the exact same set of characteristics
  • only two electrons can fit inside a single box, and they must have opposite magnetic moments
  • if two electrons have the opposite magnetic moments they cancel
28
Q

true or false; unpaired electrons are required for a material to be magnetic

A

true

29
Q

true or false; if the magnetic moments of the atoms point to random directions they cancel

A

true

30
Q

What is the effect of an external magnetic field to randomly oriented atoms

A

they align parallel

- but when the field is turned off, the random orientation returns

31
Q

What is a ferromagnet

A

they want to align magnetic moments parallel

32
Q

define magnetic domain

A

region where the magnetic moments of atoms are aligned parallel

33
Q

If a weak external magnetic field is turned off, how does this affect the conductor?

A

thermal motion aligns the domains randomly after the field turned off

34
Q

if a strong external magnetic field is turned off, how does this affect the conductor?

A

domains stay aligned after the field is removed

- the material then becomes a permanent magnet

35
Q

What is another method to make a permanent magnet?

A

stroke a piece of iron with magnet to align all the domains

36
Q

Why does dropping or heating the magnet cause the domains to weaken?

A

domains can jostle out of alignment

37
Q

what is an electromagnet?

A

type of magnet in which the magnetic field is produced by the flow of electric current
- stopping current stops magnetism

38
Q

What is a current loop

A

produces a magnetic field concentrated in the center of the loop, pointing away or towards the screen

39
Q

true or false; a strong magnetic field can be generated by winding a wire into a coil

A

true, called a solenoid

40
Q

when does a solenoid act as a magnet

A

only when current is flowing

41
Q

true or false; stationary charge in a static magnetic field experiences no net force

A

true

  • will not be moved to any direction
  • align along the magnetic field
42
Q

true or false; moving charge does not experience a force, in the magnetic field

A

false; it does experience a force

- force is perpendicular to the magnetic field and to the direction of charge motion

43
Q

What does F stand for?

A

Force on a charge moving perpendicular to the magnetic field

44
Q

what is equation for finding the force on a charge moving perpendicular to to the magnetic field?

A

F= qv B
q: charge
v: speed
B: magnetic field magnitude (T)

45
Q

true or false; if there is no current there is no movement of charge and hence no force on the wire

A

true

46
Q

what does current flowing mean

A

it means that charges experience the Lorentz force

47
Q

what is the equation for Lorentz force

A

F= I* L* B
I: current
L: length (m)
B: magnitude of magnetic field

48
Q

What is electromagnetic induction

A

changing a magnetic field can give rise to an electric current in a conducting wire
(discovered by Micheal Faraday and Joseph Henry independently in 1831)

49
Q

What can the changing magnetic field be realized by

A

a moving magnet

- or a moving conductor in a static magnetic field

50
Q

what happens eg.a moving magnet, is realized by a changing magnetic field

A

voltage is caused or induced across the conductor

  • which results in the flow of current
  • even without any battery connected
51
Q

what does Faraday’s law state?

A

-the greater the number of loops of wire that move in a magnetic field, the greater the induced voltage

52
Q

true or false; you can create electrical energy from nothing by simply moving a magnet

A

false

it is not possible

53
Q

what does Lentz law state

A
  • The induced voltage gives rise to a current. Currents always give rise to a magnetic field
  • the poles of the induced magnetic field are always such that they oppose the movement of the magnet
  • therefore there is a repulsive force one must overcome to move the magnet through the coil
  • this means mechanical work is required
54
Q

true or false; electromagnetic induction allows mechanical energy to be transformed into electrical energy

A

true

55
Q

What is a generator

A

a simple apparatus in which coil is rotated in a static magnetic field
mechanical energy is converted into electrical energy

56
Q

What happens when the string of an electrical guitar is plucked?

A

its vibration will perturb the magnetic field of the magnet. This induces a current in a coil on the pickup. The electrical signal is transmitted to an amplifier and sent to the speakers

Electromagnetism (3 decks)

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