Electrical Energy
Sasha and Tariq had all their favorite compact discs
stacked up and ready. Sasha plugged the small CD
player into the electrical outlet in the wall and then
pressed the Power button. The red power light began to
glow and the player started to hum quietly. He placed a
CD in the tray and pressed Play. The CD began to spin
and whir. In a few seconds, music poured out of the
speakers.
An hour later, Tariq walked over to put in a new CD. “Man, this thing is warm!” he said as he picked
up the player. Suddenly the music stopped. The power light went out. The CD stopped spinning.
“Hey, what’d you do to it?” yelled Sasha from across the room.
“Nothing!” said Tariq as he inspected the player. “It just stopped working!”
A moment later, Sasha’s mother walked into the room. “The electricity has gone out,” she
explained. “No electricity – no music.”
Electricity, motion, light, heat, and sound are all forms of energy. In an electrical device like a CD
player, electricity is converted into other forms of energy.
Why did everything stop working when the electricity went out?
Why was the CD player warm when Tariq picked it up?
Background Information
A CD is made of a thin layer of acrylic, aluminum, and plastic. On the surface of the CD is a thin,
single spiral track of data, which starts at the center of the CD and winds outward. These data
are read by a laser inside the CD player. A tiny drive motor spins the CD. As the CD spins, the
laser focuses on the thin spiral track and reads the data imprinted on the track. The laser itself
moves inward and outward to follow the track. The light emitted by the laser is reflected off the
surface of the CD, and changes in the reflected light are interpreted by the player as data. The
information read from a CD is sent as electrical impulses to headphones, which are converted to
the physical movement of the speaker’s components. These movements then disturb the air,
and those vibrations are interpreted by listeners as sound.
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Inquiry Problem Solution
Basic Solution
In a CD player, electrical energy is converted into mechanical energy (the spinning of the CD,
the vibrations in the speakers), light (the power lights and the laser that reads the CD), sound
(music via the speakers and the whir of the CD spinning), and heat (waste heat).
The CD player stopped working when the power went out because the CD player relied on
electrical energy from the power supply. Energy cannot be created from nothing; it can only be
converted from one form into another.
The CD player was warm because all energy conversions result in the loss of heat energy, even
when the conversion is not intentionally a conversion to heat.
Detailed Solution
Electricity can produce light by exciting atoms. When atoms are excited, some of their electrons
contain more energy than usual. When those electrons eventually return to normal, they release
their extra energy in the form of photons, which is light. CD players use electricity to do exactly
that. The laser in a CD player uses electricity to excite atoms, and this results in a stream of
photons that the player can use to read data from the CD.
Electricity can produce motion in motors. Electricity that passes through a wire generates an
electric field that can affect a magnet. Stated more simply, when electricity passes through a
wire that is aligned correctly to a magnet, it can either push or pull on a magnet. An electric
motor is basically a magnet surrounded by coils of wire. When electricity passes through the
coils of wire, it exerts a push or a pull on the magnet. Whether it pushes or pulls the magnet
depends on the direction that electricity flows through the wire. When electricity flows through
the wires in a motor, it causes a magnet to spin very rapidly. This is how a motor can produce a
spinning motion by using electricity, and therefore how a motor can be used in a CD player to
spin a CD.
Electricity can produce sound in speakers. As explained above, electricity that flows through a
coiled wire can push or pull a magnet. This is also how speakers work. Electrical impulses are
sent to a speaker. In the speaker, there is a magnet and coils of wire. Depending on the amount
and flow of the electricity, the magnet can vibrate in different ways. A CD player sends electrical
signals to the speakers in headphones, so the speakers can produce the correct vibrations
necessary to produce sound. As the magnet vibrates, that vibration is transferred to the air, and
the air transmits the vibrations to our ears.
Electricity can also produce heat. When electricity passes through wires and electrical
components, the electricity meets resistance. The amount of resistance depends on the type of
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material it is passing through. As electricity experiences more resistance, it transfers more
energy to the material it passes through. This energy causes the material to heat up. Although
heat production is not a purpose of a CD player, the CD player uses electricity and will therefore
become warm as it is used.
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