related links use the NavKnob® above to search the site for the word
will provide you with a list of links to pages within the site where the
term is mentioned or discussed.
- A type of electrical current in which the direction of the flow of
electrons switches back and forth. In the US, the current that comes
from a wall outlet is alternating; it cycles back and forth sixty times
each second. The current that flows in a flashlight, on the other hand,
is direct current (DC), which does not alternate.
- A device which takes in a weak electric signal and sends out a stronger
one. Amplifiers are used to boost electrical signals in many electronic
devices, including radios, televisions, and telephones. Both vacuum
tubes and transistors can be amplifiers, though today vacuum tubes are
rarely used for this purpose.
- The smallest possible piece of any pure element that still has the
properties of that element. Atoms are made of smaller particles including
electrons, protons, and neutrons. Differences in the numbers of these
particles create the differences between the elements. An atom is about
500-billionths of an inch, or a hundred millionths of a centimeter across.
- A special kind of vacuum tube which can be used to amplify weak electric
signals. The audion was used in the Bell phone system, as well as in
early radios and computers. It was eventually replaced in most applications
by the transistor.
- A device that stores electrical charge, using a positively charged
surface and a negatively charged surface with a gap between them. The
Leyden jar, used by early electrical experimenters (including Benjamin
Franklin) was a form of capacitor. A smaller kind of capacitor is often
used in electrical circuits.
- A tiny metal wire used in early home radio kits. Radio listeners carefully
moved the wire tips around on the surface of a crystal to just the right
spot to allow an electrical signal to travel down one wire, through
the crystal and out the other wire. If the wires were positioned on
the right spot, and it was often tough to find the right spot, the radio
signal could be heard through the earphones.
- An electrical property of particles, such as electrons and protons,
which causes them to attract and repel each other. A material with an
excess of electrons is defined to have a "negative" charge; material
with an absence of electrons (or an excess of protons) is defined as
"positive." Materials with a balanced number of electrons and protons
are called "neutral." Positive and negative charges attract each other.
That attraction can cause interesting effects at the junction between
positive and negative semiconductors. This special junction is what
makes the right configuration of semiconductors work as a transistor.
- A string of electronic devices such as transistors, resistors, capacitors,
and diodes connected by wires so that current can run through it in
a complete loop. Circuits can be simple or complex. The wiring connecting
a switch to a light to the power source and back to the switch is a
simple circuit; opening the switch breaks the circuit and stops the
current flow. Even a computer chip is simply an extremely complicated
network of circuits.
- Any material that easily allows the flow of electricity. Metals are
good conductors. Such materials conduct electricity because electrons
can move from one atom of a conductor to the next, forming an electric
- A chunk of solid material in which all the atoms are lined up in an
orderly pattern like rows of oranges in a grocery store. Transistors
are made out of semiconductor crystals. Growing perfect germanium and
silicon crystals with no defects or unwanted impurities is key to building
a working transistor.
- The flow of charge carriers (holes or electrons) through a conducting
wire or crystal.
- Rectifier. An electronic device with two wires or terminals. A rectifier
allows electrical current to flow through in only one direction and
is used for converting alternating current into direct current. Rectifiers
were important for use in radios, which required direct current to power
the amplifiers driving speakers or headphones.
Direct Current (DC):
- Current which moves in a single direction in a steady flow. Normal
household electricity is alternating current (AC) which repeatedly reverses
its direction. However, many electronics devices require DC, and therefore
must convert the current into DC before using it. Diodes are used to
convert AC to DC.
- Deliberately adding a very small amount of foreign substance to an
otherwise very pure semiconductor crystal. These added impurities give
the semiconductor an excess of conducting electrons or an excess of
conducting holes (the absence of conducting electrons) which is crucial
for making a working transistor.
- The region around any electrically charged material contains an electric
field that affects other charged objects. The field around a negatively
charged material pulls positively-charged objects in toward the material,
while negatively-charged objects are pushed away. Around a positively
charged material, on the contrary, negative objects are attracted and
positive objects are repelled. The strength of the field gets rapidly
weaker as one moves further away from the charged material.
- Information expressed through changes in an electric current. Information
can be encoded in on-and-off switches of current, in the amplitude of
the current, or in other easily-detectable changes. Sound waves, for
example, can be converted to electricity by a microphone and sent as
an electrical signal through the wires of a stereo to the speakers.
- An electrical lead or wire attached to any electronic device or circuit
through which current may flow in or out.
- Electrons are one of the particles that makes up an atom and particles
that, in motion, can form an electric current. An electron is 2000 times
lighter than the lightest atom.
- Any of over a hundred fundamental materials containing only one kind
of atom. Some common elements are oxygen, gold, hydrogen, and silicon.
All other materials are made of compounds or mixtures of elements. Water,
for example, is made of two hydrogen atoms attached to one oxygen atom.
- The most common type of modern transistor, and the type of transistor
used in integrated circuits. The field-effect transistor is so named
because an incoming weak electrical signal creates an electrical field
across a section of semiconductor. This field causes a second electrical
current to flow across the semiconductor, identical to the first weak
signal, but stronger.
- A semiconductor device which can take alternating current and turn
it into direct current but which also stops letting any current through
once a certain voltage is reached. The diode is made of four layers
of alternating types of semiconductor.
- A chemical element that acts as a semiconductor, meaning sometimes
it conducts electricity and sometimes it doesn't. The first transistors
were all made out of germanium.
- When an array of atoms in a crystal is missing a conducting electron,
it's said to have a "hole." Since conducting electrons are negative,
holes are positive. Even though holes are an absence of a conducting
electron, scientists often talk about holes flowing as if they were
- Any material that does not conduct electricity. Glass and rubber are
common insulators. These materials are made of atoms which don't allow
electrons to move freely, which means there can be no electric current.
- A collection of transistors and electrical circuits all built onto
a single crystal. Today's integrated circuits are no more than a centimeter
long, and they can carry millions of microscopic transistors. All computers
have integrated circuits inside.
- The second type of transistor built, and a direct ancestor of modern
day transistors. It consists of two sections of one type of semiconductor
(N- or P-) around a middle slab of the other type. The junctions between
the semiconductor sections cause an incoming weak electrical signal
to be amplified.
- A circuit of transistors and other electrical components on a chip
that can process programs, remember information, or perform calculations.
- A semiconductor which has an excess of conduction electrons. A semiconductor
can be made into N-type by adding trace amounts of another element to
the original semiconductor crystal. Today's transistors all require
sections of both N-type and P-type semiconductors.
- A semiconductor which has an excess of conducting holes. It is created
by adding trace amounts of other elements to the original pure semiconductor
crystal. Today's transistors all require sections of both N- type and
- The very first type of transistor ever made, invented by John Bardeen
and William Brattain. So-called because it consists of two metal points
making light contact with the surface of a germanium crystal.
- See Diode
- A material that conducts more than an insulator but less than a conductor.
Some semiconductors conduct at some times but not at others. Some common
semiconductors are silicon and germanium. Transistors are made out of
- Silicon is one of the most common elements on Earth in the Earth's
crust, it's second in mass only to oxygen and can be found in any quartz
crystal. Beach sand is largely silicon. Silicon is also the semiconductor
material out of which almost all modern transistors are made.
- Relating to the properties of solid, usually crystalline, materials
including semiconductors. Solid state science is often a mixture of
physics, and chemistry, and materials science.
- Transistors are tiny electrical devices that can be found in everything
from radios to robots. They have two key properties: 1) they can amplify
an electrical signal and 2) they can switch on and off, letting current
through or blocking it as necessary.
- What Bell called the first point-contact transistors they built. These
were installed into the Bell Phone system, and given to the military
and scientists for other purposes as well - but the Type-A transistor
was never widely used.
- Voltage is a measure of the energy required to move a charge from
one point to another. A difference in the amount of electric charge
between two points creates a difference in potential energy, measured
in "volts," which causes electrons to flow from an area with more electrons
to an area with fewer, producing an electric current.
Back To Top
1999, ScienCentral, Inc, and The American Institute of Physics.
portion of this web site may be reproduced without written permission.
NavKnob is a trademark of ScienCentral, Inc. All Rights Reserved.