2. PRINCIPLES OF ELECTROMAGNETIC
INDUCTION (EMI) IN RECORDING SYSTEMS
In recording systems and technology, whether
analog or digital, magnetic recording is the name
of the game. In a magnetic recording of a music
or video input, the signal is converted into
electrical signals via transducers like a
microphone.
3. PRINCIPLES OF ELECTROMAGNETIC
INDUCTION (EMI) IN RECORDING SYSTEMS
It then passes through a magnetic recorder like
the read/write head of a video disc player,
converting and recording the electrical signals
into a magnetic pattern on a medium like a laser
disc or a cassette tape. During recording and
playback, the magnetic medium moves from the
supply reel to the take-up reel.
4. PRINCIPLES OF ELECTROMAGNETIC
INDUCTION (EMI) IN RECORDING SYSTEMS
The signals change the magnetic field that cuts
through the head inducing a changing electric
current in the head relying on the speed and
strength of the magnetic field. The induced
electrical currents are then amplified and sent to
an audio only or an audio-video monitor where
another transducer, like a speaker, changes the
electrical signals to the desired output.
9. WORKING PRINCIPLE OF A
CONDENSER MICROPHONE
- The varying sound pressure changes the spacing between a
thin metallic membrane and a stationary plate, producing
electrical signals which “copy” the sound pressure.
Salient Features: Works with a wide range of sound frequencies.
Although expensive, it is considered as the best microphone for
recording applications.
10. WORKING PRINCIPLE OF A
DYNAMIC MICROPHONE
The varying sound pressure moves the cone diaphragm
and the coil attached to it within a magnetic field,
producing an electromotive force that generates
electrical signals which “copy” the sound pressure.
Salient Features: The inverse of a dynamic loudspeaker
and relatively cheap and rugged.
11. WORKING PRINCIPLE OF A
HEADPHONE OR AN EARBUD
Wires carry the audio signal from the stereo into the coil and
back again. The coil around the plastic cone becomes an
electromagnet when current passes through it. And because the
coil is within a magnetic field, a force is generated on the coil. In
response to the audio signal, the coil moves together with the
flexible flat crinkly cone moving the air within the
headphone/earbud enclosure and in the ear canal producing
sound
12. WORKING PRINCIPLE OF A
HEADPHONE OR AN EARBUD
Salient Features: Headphones and earphones are
small loudspeakers clamped over the ear/s.
Basically, each speaker consists of stereo wires,
plastic cone diaphragms, coils attached to the
cone, and magnets built inside cased or padded
sound chambers.
13. WORKING PRINCIPLE OF A
STUDIO MONITOR OR A SPEAKER
The electric current imaging the audio signal is
sent through the coil that is within the magnetic
field. A force is generated that moves the magnet
and the cone attached to it producing the sound
corresponding to the analog or digital signal.
14. WORKING PRINCIPLE OF A
STUDIO MONITOR OR A SPEAKER
Salient Features: The studio monitor is a dynamic reference
speaker designed to produce an accurate image of the sound
source. Most hobby studio use the active type studio monitor. It
has a built-in amplifier and functions when plugged into an
outlet and a sound source. A dynamic speaker, like the studio
monitor, has the same essential parts as a dynamic microphone.
But unlike the microphone or headphone where the voice coil is
attached to the cone diaphragm, on the studio monitor, it is the
permanent magnet that is attached to the cone while the coil is
wound around a fixed core.
16. In 1831, two physicists,
Michael Faraday in England
and Joseph Henry in the
United States,
independently discovered
that magnetism could
produce an electric current
in a wire. Their discovery
was to change the world by
making electricity so
commonplace that it would
power industries by day and
light up cities by night.
17. Electric current can be produced in a wire by simply
moving a magnet into or out of a wire coil.
37.1 Electromagnetic Induction
18. No battery or other voltage
source was needed to produce a
current—only the motion of a
magnet in a coil or wire loop.
Voltage was induced by the
relative motion of a wire with
respect to a magnetic field.
37.1 Electromagnetic Induction
19. The production of voltage depends only on the relative motion
of the conductor with respect to the magnetic field.
Voltage is induced whether the magnetic field moves past a
conductor, or the conductor moves through a magnetic field.
The results are the same for the same relative motion.
37.1 Electromagnetic Induction
20. The amount of voltage induced depends on how quickly the
magnetic field lines are traversed by the wire.
• Very slow motion produces hardly any voltage at all.
• Quick motion induces a greater voltage.
Increasing the number of loops of wire that move in a
magnetic field increases the induced voltage and the current
in the wire.
Pushing a magnet into twice as many loops will induce twice
as much voltage.
37.1 Electromagnetic Induction
21. Twice as many loops as another means twice as much
voltage is induced. For a coil with three times as many loops,
three times as much voltage is induced.
37.1 Electromagnetic Induction
22. We don’t get something
(energy) for nothing by simply
increasing the number of loops
in a coil of wire.
Work is done because the
induced current in the loop
creates a magnetic field that
repels the approaching magnet.
If you try to push a magnet into
a coil with more loops, it
requires even more work.
37.1 Electromagnetic Induction
23. Work must be done to move the magnet.
a.Current induced in the loop produces a magnetic field
(the imaginary yellow bar magnet), which repels the bar
magnet.
37.1 Electromagnetic Induction
24. Work must be done to move the magnet.
a.Current induced in the loop produces a magnetic field
(the imaginary yellow bar magnet), which repels the bar
magnet.
b.When the bar magnet is pulled away, the induced
current is in the opposite direction and a magnetic field
attracts the bar magnet.
37.1 Electromagnetic Induction
25. The law of energy conservation
applies here.
The force that you exert on the
magnet multiplied by the distance
that you move the magnet is your
input work.
This work is equal to the energy
expended (or possibly stored) in the
circuit to which the coil is connected.
37.1 Electromagnetic Induction
26. If the coil is connected to a resistor, more
induced voltage in the coil means more
current through the resistor.
That means more energy expenditure.
Inducing voltage by changing the
magnetic field around a conductor is
electromagnetic induction.
37.1 Electromagnetic Induction
28. is a property of a material that
enables to attract or repel other materials.
The presence and strength of the material’s
magnetic properties can be observed by
the effect of the forces of attraction and
repulsion on other materials.
29. A magnetic field is produced by the motion of
electric charge.
36.3 The Nature of a Magnetic Field
30. Magnetism is very much related to
electricity.
Just as an electric charge is
surrounded by an electric field, a
moving electric charge is also
surrounded by a magnetic field.
Charges in motion have associated
with them both an electric and a
magnetic field.
The Nature of a Magnetic Field
31. Electrons in Motion
Where is the motion of electric charges in a common
bar magnet?
The magnet as a whole may be stationary, but it is
composed of atoms whose electrons are in constant
motion about atomic nuclei.
This moving charge constitutes a tiny current and
produces a magnetic field.
The Nature of a Magnetic Field
32. More important, electrons can be thought of as spinning
about their own axes like tops.
A spinning electron creates another magnetic field.
In most materials, the field due to spinning
predominates over the field due to orbital motion.
The Nature of a Magnetic Field
33. In an atom, the intrinsic magnetic field is
mostly due to the
in the half- filled orbital shell
where electrons are unpaired and their tiny
intrinsic magnetic moments point in the
same direction, thus orbital magnetic field
arise.
34. When the atoms of metals like
are placed within an external magnetic
field, the weaker domains unify with the stronger
domains. These line up more uniformly inducing
greater magnetic field strength. Materials made from
these elements and its alloys are classified as
and make strong permanent
magnet
35. Magnets brought near materials that contain one of
the ferromagnetic metals will induce magnetism.
also makes iron filings and
compass pointers align themselves along the
magnetic field lines that caused induction. The
magnetic field lines go out of the north-seeking
poles and loops back continuously going to the
other south-seeking end of the magnet closing the
loop inside out.
36. The difference between a piece of ordinary iron and an iron magnet is the
alignment of domains.
• In a common iron nail, the domains are randomly oriented.
• When a strong magnet is brought nearby, there is a growth in size of
domains oriented in the direction of the magnetic field.
• The domains also become aligned much as electric dipoles are aligned in
the presence of a charged rod.
• When you remove the nail from the magnet, thermal motion causes most of
the domains to return to a random arrangement.
Magnetic Domains
37. Permanent magnets are made by simply placing pieces
of iron or certain iron alloys in strong magnetic fields.
Another way of making a permanent magnet is to stroke
a piece of iron with a magnet.
The stroking motion aligns the domains in the iron.
If a permanent magnet is dropped or heated, some of
the domains are jostled out of alignment and the
magnet becomes weaker.
Magnetic Domains
38. The arrows represent
domains, where the
head is a north pole
and the tail a south
pole. Poles of
neighboring domains
neutralize one
another’s effects,
except at the ends.
Magnetic Domains
39. A is a field of force
produced by a magnetic object or particle, or by a
changing electrical field and is detected by the
force it exerts on other magnetic materials and
moving electric charges. Magnetic field sources are
essentially dipolar in nature, having a north and a
south magnetic poles.
40. Iron filings sprinkled on a sheet of paper over a bar magnet will
tend to trace out a pattern of lines that surround the magnet.
The space around a magnet, in which a magnetic force is
exerted, is filled with a magnetic field.
The shape of the field is revealed by magnetic field lines.
Magnetic Fields
43. Magnetic field patterns for a pair of magnets when
a. opposite poles are near each other
b. like poles are near each other
Magnetic Fields
44. The direction of the magnetic field
outside a magnet is from the north
to the south pole.
Where the lines are closer together,
the field strength is greater.
The magnetic field strength is
greater at the poles.
If we place another magnet or a
small compass anywhere in the
field, its poles will tend to line up
with the magnetic field.
Magnetic Fields
