Unit 5 Flashcards
1
Q
foundational concept of magnetism
A
a moving electric charge creates a magnetic field
2
Q
how can you create a magnet?
A
by wrapping a current carrying wire around an iron bar
3
Q
magnets have…
A
two poles. north and south. same poles repel, opposite poles attract
4
Q
magnetic domains
A
region in which the magnetic fields of atoms are grouped together and aligned
5
Q
what is the ability of an object to become magnetized due to?
A
magnetic domains
6
Q
what is a magnetic field defined by?
A
- its direction
- its magnitude and strength
7
Q
1 Tesla Unit =
A
1N/1Am (Amp meter)
8
Q
when do northern glowing lights occur?
A
when charged particles move in the Earth’s magnetic field
9
Q
what happens when a charged particle moves across magnetic field lines?
A
the force of the field acts on the particle, and the charged particle experiences a deflecting force
10
Q
what happens when a charged particle is at rest or moves parallel to the magnetic field?
A
the magnetic force does not exert a force on the particle
-they will not interact with static magnetic field
11
Q
what do magnitude and direction of force depend on?
A
velocity of the charged particle
12
Q
every wire that carries a current must also…
A
generate a magnetic field
13
Q
electric motor
A
as current passes through a wire, it generates a magnetic field that deflects a magnet and turns a motor
14
Q
how does an electric motor work?
A
by controlling the current, the magnet can spin, which turns the shaft and allows work to be done
15
Q
particle accelerator
A
magnetic field is used to direct the fields around circular accelerator rings
16
Q
how can one detect currents?
A
by watching deflected magnets
17
Q
why do magnetic fields exert force on current-carrying wires?
A
they carry many moving charged particles
18
Q
magnets…
A
- can attract and repel without touching
- strength of interaction depends on the distance of separation of the two magnets
- magnetic poles produce magnetic forces
19
Q
can magnetic poles be isolated?
A
No, compared to electric charges, which can be isolated
-north pole never exists without the south pole, and vice versa
20
Q
magnetic field
A
space around magnets, in which a magnetic force is exerted
21
Q
how are permanent magnets made?
A
by placing pieces of iron or certain iron alloys in strong magnetic fields
22
Q
since moving charge produces a magnetic field, when many charges are in motion…
A
current flows through a conductor and electric current produces a magnetic field
23
Q
electromagnet
A
current-carrying coil of wire with many loops
24
Q
sideways deflecting force
A
a force that acts on a moving charged particle that acts perpendicular to both the magnetic field and the electron velocity
25
How do TV tubes work?
- uses the sideways deflecting force principal
| - steer electrons onto the inner surface of screens and provides a picture
26
galvanometer
measures the presence of current.
| -If current is present, it will deflect a magnetic needle (like a compass needle).
27
since all atoms have spinning electrons, why are not all atoms tiny magnets
in most atoms, various fields cancel one another because the electrons spin in opposite directions, cancelling each other out
28
why do some pieces of iron behave as magnets, while other pieces of iron do not?
alignment of domains.
- a common iron nail has domains that are randomly orientated.
- The magnetic domains in the iron magnet have been aligned so they all point in the same direction.
29
how can a piece of iron be induced into becoming a magnet?
by simply placing it in a strong magnetic field. If you place a paperclip near a magnet, it itself will become a magnet because the domains become aligned in the magnetic field.
30
with respect to an electric and a magnetic field, how does the direction of a magnetic force on a charged particle differ from the direction of the electric force?
Magnetic - force is perpendicular to the field; electric - force is parallel to the field.
31
what role does earth's magnetic field play in cosmic ray bombardment
Earth's magnetic field deflects charged particles
32
magnetic declination
discrepancy between the orientation of a compass and true north
33
what is the probably cause of earth's magnetic field?
moving charges looping around within Earth create its magnetic field
34
What kind of field surrounds an electric charge a) when it is sitting still, and b) when it is moving?
a) sitting still: surrounded by an electric field.
| b) moving: surrounded by both an electric field and a magnetic field.
35
How do the input and output parts of a generator and motor compare?
A motor and a generator are the same thing, just acting in different directions.
generator: input mechanical energy and get out electricity (electric current).
motor: input electricity and get out mechanical energy.
36
what does moving a magnetic field through a loop of wire do?
applies a force to the charges in the wire and causes the charges to move along the wire
37
what did Faraday find?
that you get more voltage if
a) have more loops of wire
b) use thicker wire
c) move magnet in and out quickly
- electric motors and generators work on this principle of electromagnetic induction
38
how does moving a magnet into a loop of wire cause an electric current?
when an electric charge moves in relation to a magnetic field, the field exerts a force on it.
-the charge moves as a result of this force and the only direction they can move is along the wire
39
how to transmit a required amount of electrical power?
can either transmit high voltages and low currents or low voltages with high current
-more efficient to use electrical power with high voltage and low current
40
modern electric grid
generates power at relatively low voltages, uses transformers to turn it into high voltage power, transmits along power lines, then uses transformers again to reduce it to the voltages required by our houses and businesses (usually 110-120V)
41
transformers
physical devices with a permanent magnet and two loops of wire that either increase or decrease voltage
-for increasing or decreasing voltage through an electromagnetic induction
42
what is voltage related to?
the number of loops.
| ex: if input side has 1 loop of wire, voltage will be 1 volt
43
what does production of voltage depend on?
the relative motion of the conductor with respect to the magnetic field
44
what does the amount of voltage induced depend on?
how quickly magnetic fields are transversed by the wire
45
input work is equal to...
the force exerted on a magnet * the distance that moves the magnet
-the input work is equal to the energy expanded (or stored) in the circuit to which the coil is connected
46
electromagnetic induction
phenomenon of inducing voltage by changing the magnetic field around a conductor
47
Faraday's law
The size of the voltage produced is proportional to the number of loops, the thickness of the wire and the rate at which the magnetic field changes.
48
what does the amount of electromagnetic induction depend on?
the induced voltage and the resistance of the coil and the circuit to which it is connected
49
generator
machine that produces electric current by rotating a coil within a stationary magnetic field
50
deflected wire
motor effect. occurs when a current moves through a magnetic field
51
relationship between primary and secondary voltages with the relative number of turns
(primary voltage)/(number of primary turns) = (secondary voltage)/(number of secondary turns)
52
why is almost all electric energy sold today the form of alternating current?
because of the ease with which it can be transformed from one voltage to another
53
what is an electromagnetic wave composed of?
oscillating electric and magnetic fields that regenerate each other. no medium required
54
speed of electromagnetic radiation
the speed of light
55
light
electromagnetic waves between the range of 4.3*10^14 to 7*10^14 vibrations/second of frequencies
56
Why can't a current be created with a magnet at rest inside a loop of wire?
If the magnet is at rest, the magnetic field and the electrons are not moving relative to each other and the electrons will feel no force from the magnetic field.
57
what does an electric motor rely on?
a magnetic field and loop of wire moving in relation to each other
58
what does an electric generator rely on?
a magnetic field and loop of wire moving in relation to each other
59
Why do you have to move a magnet in and out of a generator for it to work?
Generators rely on CHANGING magnetic fields to generate current. The magnet must be MOVING to keep generating voltage and current.
60
Why doesn't direct current work with transformers?
Like the simple magnet and wire-loop generators, transformers rely on the CHANGE of voltage in one loop to generate voltage in the other loop. Direct current is like a magnet that stays in one place in a loop of wire.
61
How can you increase the voltage that is induced in a coil?
To increase the voltage that is induced in a coil you can increase the number of loops, increase the thickness of the wire, or increase the rate at which the magnet moves in and out of the loop.
62
If you are moving a magnet in and out of a loop of wire to create a current, what will you experience if you double the number of loops of wire?
In addition to increasing the induced voltage, you will feel greater resistance as you move the magnet.
63
What are the three main components of a generator?
A generator also has a magnetic field, moving charges, and a magnetic force
64
What are the three main components of a motor?
a magnetic field, moving charges, and magnetic force.
65
What is incorrect about saying "a transformer converts electrical current, voltage, and energy from one level to another"?
A transformer changes electric current and voltage but the energy stays the same.
66
What are the advantages of transmitting power using high voltage?
Since we need a certain power output and P = IV, the larger voltage means we need less current. Smaller currents result in less resistance and less heating of wires.
67
A transformer has 50 turns in its primary coil and 250 turns in its secondary coil. A 12V AC source is connected to the primary coil. Find the following:
a. the AC voltage available at the secondary coil.
b. the current in a 10 ohm device connected to the secondary coil.
c. the power supplied to the primary coil.
a. 250/50 = 5X, so the output is 60V.
b. V = IR so I = V/R = 60/10 = 6 amps.
c. P = IV = 6 x 60 = 360 watts.
68
how does a transformer work?
works by inducing a changing magnetic field in one coil, which induces an alternating current in a nearby second coil
69
what happens when a compass needle is brought close to a current carrying wire?
the compass needle is deflected one way or another depending on the direction of the current.
70
what is the direction of the magnetic field inside a magnet
from the south pole to the north pole
71
what is the direction of the magnetic field outside a magnet?
from the north pole to the south pole
72
according to faraday's law, what can you change in order to increase the induced voltage in a coil?
- number of loops
- cross-sectional area of each loop
- rate at which magnetic field changes
73
is electricity a source of energy?
no. electricity is a form of energy or a way of transferring energy but it is not a source. The energy from a generator comes from the work done.
74
another name for the generator effect
law of induction
75
a step up transformer has
more turns in the secondary coil than in the primary coil
76
why is power transferred long distances at very high voltage?
high voltage wires allow us to reduce the current, which means less resistance and heat
77
what is the source of all electromagnetic waves?
accelerating electric charges
