Download Earphone in a Lid - Expanded Science Behind the

EARPHONE IN A LID
The expanded science behind the activity
(Bolded words in parentheses are the proper scientific terms.)
Background information on sound and sound production:
When vibrations are strong enough to be perceived by an ear and brain then a sound will be “heard”.
This forms the basis of the riddle “Does a falling tree make a sound if no one is around to hear?” The
falling tree causes the air to vibrate, to move back and forth and thus send out mini air pressure waves,
spreading out like the water waves from a dropped stone, but in 3 dimensions. Unless the pressure
waves reach a person or animal with enough force to be perceived as sound, then there is no “sound”
as would be made by a falling tree!
Usually the word “sound” is used to refer to the pressure wave that occurs before the sound is actually
perceived. The term “sound” or “sound waves” will often be used in place of the more scientifically
correct terms “pressure” or “mechanical” waves.
An electrical speaker is a device that converts electrical energy into mechanical energy. The mechanical
energy generates pressure waves that can be perceived as sound. For humans these waves have to
have a back and forth motion (frequency) in the approximate range between 20 to 20,000 cycles per
second (between 20 Hz and 20,000 Hz) to be heard.
A sound’s pressure wave begins when an object’s movement, such as vocal cord, a
plucked string, vibrating reed, drum surface, or bass horn player’s buzzing lips, causes a
repetitive back and forth motion, called a vibration. The vibration will cause the medium
that is in contact with the vibrating object to also vibrate. For humans the medium is usually
a gas (air), but sound can potentially be transmitted through material that is in any of the 4
states of matter; gas, liquid, solid, or plasma. Sound cannot be transmitted through a
Vibrating reed
vacuum as there is no matter present to transmit the wave from one place to another.
The vibrations of matter take the form of alternate compressions and
Low pressure
area
expansions of groups of molecules and/or atoms. For the examples
mentioned earlier the vibrating objects are alternately pushing the nearby
air on one side, compressing the nearby molecules together, and then
moving back in the opposite direction creating space into which the air
High pressure
molecules can spread out. The back and forth air movement causes tiny
area
variations in the air pressure as the air molecules are pressed together
(resulting in higher air pressure locally) and then as the air molecules
Vibrating reed
Low pressure
move apart (creating, locally lower air pressure). These alternating
over time
area
pressure variations spread out from the source of the sound in a similar
fashion to the waves from a dropped pebble on the surface of a pond, but
through the air, in 3 dimensions. In the pond the water molecules move,
essentially, up and down while the circular waves travel outward toward
High pressure
the edges of the pond. The waves decrease in height (amplitude) the
area
farther the waves are from the originating source, which is true for both
water and sound waves.
A sound’s compression waves are more accurately modeled using a stretched out spring toy where a
few coils at one end are pushed together and then let go. The compressed coils (modeling high
pressure) expand (modeling low pressure) causing a compression of the coils nearby. The process
repeats and continues along the length of the spring. Each coil only moves a short distance back and
forth. In the same way the individual air molecules only move a short distance back and forth but the
pressure waves can travel a much longer distance.
A larger vibrating surface will move more air than a smaller surface, which explains why large guitars
with big hollow bodies are louder than small ukuleles.
Earphone in a Lid, The expanded science behind the activity, page 1
© 2013, RAFT
The slight variations in air pressure are enhanced by being “funneled” inward by the outer ear, directed
toward the eardrum, which makes the eardrum vibrate back and forth. The movement of the eardrum
moves tiny bones which then vibrate the fluid in a chamber filled with tiny hairs. The movement of the
hairs triggers electrical impulses that are sent to the brain where the impulses are interpreted as a
sound. Sound travels in the air at approximately 1200 kilometers (760 miles) per hour.
Background information on electrons:
Through experimentation scientists have learned that all the different stuff (matter) that makes up our
world has been created using a little over 100 different basic building blocks (called elements). Each
element, such as gold, aluminum, and calcium, has a unique combination of properties including how
much a set amount weighs (which is related to the element’s mass) and how readily the element will
combine with other elements. The smallest piece of an element that still possesses the element’s key
properties is called an atom. Every atom is made up of just 3 types of even smaller particles,
electrons, protons, and neutrons. The lightest particle is the electron, which circles around a tightly
packed core (the nucleus) that contains an equal number of protons and a related, equal more or less,
number of neutrons. Although the electrons are often pictured orbiting in the manner of planets circling
the Sun the more accurate picture would be of a whirling mist of electrons orbiting around the nucleus.
Two or more atoms can combine to form the smallest pieces (molecules) of all other types of matter.
Electrons and protons have an electrical property called “charge”. Since the atom contains an equal
number of electrons, each with a single negative charge, and an equal number of protons, each with a
single positive charge atoms usually have no overall net charge (are neutral). The equal number of
positive and negative charges balance (“cancel”) each other.
Essentially all things contain electrons. Objects made of metal have many, many electrons that can
easily be made to move in one direction within the metal object and can even transfer to another metal
object. Conductors such as wires made of metal provide a path for electrons to move or, more
accurately, bump along like a long line of “bumper cars”. Wires are often covered with an insulator or
non-conducting material that does not allow electrons to move about easily.
Electrons can be made to move in one general direction in wires when a source of electrical “push/pull”
(voltage) is connected to the wire. Examples of voltage sources are batteries and solar cells.
Background information on magnetism:
We commonly label materials as being either non-magnetic, magnetic, or a magnet. However all
matter really is magnetic, even if only at the atomic or sub-atomic level. This is true because all matter
contains moving particles (such as electrons and protons) that have charges (negative [-] or positive
[+]). When a charged particle moves a magnetic field is automatically created, which surrounds the
particle. In an atom or molecule all the individual magnetic fields of the particles are usually oriented in
random (different) directions so there is no (or almost no) overall magnetic field. Since most elements
are only very, very weakly magnetic, at best, we considered them to be non-magnetic.
Commonly available items that are magnetic are most often made of steel, an alloy containing iron. It
is important that the learners realized that other elements are also magnetic, such as nickel and cobalt.
Certain Canadian coins are magnetic because of having very high nickel content, higher than the US
nickel coin. In magnetic materials the sub-atomic magnetism can show up in items containing these
elements instead of being cancelled out. Each magnetic material has many microscopic areas called
domains. The atoms in a single domain have their magnetic fields oriented in the same direction.
Usually, magnetic fields of all the other domains will be pointing in different directions so the material,
overall, does not act like a magnet, but a magnet will attract the material.
N
Un-magnetized magnetic
material (fields cancel)
S
Permanent Magnet
Earphone in a Lid, The expanded science behind the activity, page 2
N
S
Magnetized magnetic material
(fields combine)
© 2013, RAFT
To make a magnet, the magnetic orientation of a magnetic material’s different domains must line up
more strongly in one direction. This can happen naturally; when certain bacteria create a single ironcontaining crystal and in the mineral magnetite, the original lodestone. Bringing a magnet near
magnetic material will cause the domains to line up. When the magnet is removed the domains may
reorient. Currently, permanent magnets are made by using a powerful electromagnet to line up the
material’s domains.
Each magnet has at least two areas where the magnetic field is the strongest, called “poles,” with one
being labeled the north pole and the other the south pole. These poles are usually on opposite sides
or ends of the magnet. Like (same) poles (north/north or south/south) of two magnets will repel each
other while the unlike poles (north/south and south/north) will attract each other. The attractive and
repelling force will increase as the distance between the poles decreases.
Magnetic materials and magnets are mutually attracted to each other.
Electrons moving in a wire will create a magnetic field around the wire. By forming the wire into a coil (a
solenoid) the magnet fields of the individual wires can be combined to create a stronger overall
magnetic field. The magnetic field will be stronger if the turns of the coil are as close as possible to each
other. The Earphone in a Lid uses wire that has a very thin insulated coating that is painted on rather
than the more common ( and much thicker) plastic sleeve. Such coated wire is called “magnet wire” not
because the wire is magnetic or a magnet, but because the wire will make stronger magnetic fields
when shaped into a coil. The term “solenoid” is used in physics to describe a coil while a coil wrapped
around an iron core (a bolt for example) is called an electromagnet.
An energized (powered by a voltage source) electromagnet will have north and south magnetic poles at
either end. The poles will act in the same fashion as a permanent magnet’s poles. Like poles will repel
and unlike poles will attract each other. The stronger the electromagnet and/or the magnet the stronger
will be the attraction and repelling.
In order to create louder sounds with smaller magnets modern earphones and speakers sometimes use
rare earth magnets (magnets containing rare earth elements), which have much stronger magnetic
fields than other magnets of an equal size.
Earphone in a Lid, The expanded science behind the activity, page 3
© 2013, RAFT