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Flashcards in Magnetism Deck (56):
1

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

true

2

what is the equation for cost of electricity?

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

3

Define magnetism

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

4

What is a permanent magnet

object that displays persistent magnetism

5

what are the two magnetic regions

south and north pole

6

true or false; magnetic monopoles exist

false
- there is no such thing

7

why don't magnetic monopoles exist

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

8

when do magnets experience a force

when around other magnets

9

what are the fundamental laws of magnetism

like poles repel
opposite poles attract

10

What is a magnetic force

mediated by a magnetic field
- surrounds a magnet (just like E-field surrounds a charge)

11

what is the symbol for magnetic field

B

12

true or false; magnetic field has a magnitude and direction

true

13

Which direction do the arrows (field lines) go

north to south pole

14

What are the units for magnetic fields

Tesla (T) = 10 000 Gauss (G)

15

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

true

16

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

false; south pole is pushed against the field lines

17

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

true

18

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?

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

19

what causes an electric charge

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

20

What did Oersted show?

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

21

What was Oersted's demonstration

he placed a magnetic needle beneath a current carrying wire

22

true or false; an electric current produces a magnetic field

true

23

What is current

the flow of electric charge

24

what is the source of all magnetism

the movement of electric charge

25

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

- electrons: spin angular momentum
- orbitals: orbital angular momentum

26

what are electrons

fermions

27

describe the characteristics of an electrons

- 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

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

true

29

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

true

30

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

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

31

What is a ferromagnet

they want to align magnetic moments parallel

32

define magnetic domain

region where the magnetic moments of atoms are aligned parallel

33

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

thermal motion aligns the domains randomly after the field turned off

34

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

domains stay aligned after the field is removed
- the material then becomes a permanent magnet

35

What is another method to make a permanent magnet?

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

36

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

domains can jostle out of alignment

37

what is an electromagnet?

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

38

What is a current loop

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

39

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

true, called a solenoid

40

when does a solenoid act as a magnet

only when current is flowing

41

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

true
- will not be moved to any direction
- align along the magnetic field

42

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

false; it does experience a force
- force is perpendicular to the magnetic field and to the direction of charge motion

43

What does F stand for?

Force on a charge moving perpendicular to the magnetic field

44

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

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

45

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

true

46

what does current flowing mean

it means that charges experience the Lorentz force

47

what is the equation for Lorentz force

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

48

What is electromagnetic induction

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

What can the changing magnetic field be realized by

a moving magnet
- or a moving conductor in a static magnetic field

50

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

voltage is caused or induced across the conductor
- which results in the flow of current
- even without any battery connected

51

what does Faraday's law state?

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

52

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

false
it is not possible

53

what does Lentz law state

-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

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

true

55

What is a generator

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

56

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

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