Download Electronics Theory

Electronics Theory
Bangor High School
Ali Shareef
4/7/06
Atoms
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Composed of neutrons, protons, and
electrons.
Protons and electrons comprise the
majority of the atom’s weight. Electrons
weigh virtually nothing.
Protons and neutrons reside in the
nucleus.
Electrons orbit the nucleus.
Atoms
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Neutrons don’t have a charge.
Protons have a positive charge.(+)
Electrons have a negative charge. (-)
Opposite charges attract. Electrons are
attracted to the protons. This is the
force that keeps the electrons in orbit
around the neutrons.
Atoms
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The atoms tries to balance its charges
and be neutral.
Ex. Carbon has 6 Protons and 6
Electrons.
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6 Protons = +6 Charge
6 Electrons = -6 Charge
The protons’ charges cancel the electrons’
charges and you have a net charge of 0.
Atoms
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It is possible that an atom can lose an
electron due to interaction by atoms of other
elements. (This requires a large amount of
force.)
Ex: Carbon – 6 Protons and 5 Electrons
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6 Protons = +6 Charge
6 Electrons = -5 Charge
The protons’ charges cancel the electrons’ charges
and you have a net charge of +1.
Atoms
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In order to balance itself the Carbon
atom of the previous example will be
actively “searching” for an electron.
Atoms
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It is possible that an atom can gain an
electron due to interaction by atoms of other
elements. (This requires a large amount of
force.)
Ex: Carbon – 6 Protons and 8 Electrons
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6 Protons = +6 Charge
6 Electrons = -8 Charge
The protons’ charges cancel the electrons’ charges
and you have a net charge of -2.
Atoms
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Tremendous force between the 6 protons and
6 internal electrons. of a Carbon atom.
The force between the 6 protons and the 2
extra electrons is much weaker.
These 2 extra electrons are known as the
valence electrons.
If the carbon atom with a missing electrons
comes near this atom, it will pull off one of
the electrons of this atom.
Batteries
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Composed of two compartments filled
with different chemicals.
One compartment has chemicals that
have excess electrons. (-) Net charge.
The other compartment has chemical
that don’t have enough electrons.
(+) Net charge.
Batteries
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The atoms in the (+) compartment are
desperate for (-) electrons in the other
compartment.
This force between the positive and negative
compartments is known as voltage.
The greater the charge difference between
the two compartments the greater the
voltage.
When a wire is place between the (+) and
the (-) terminals, the electrons rush to the
(+) compartment.
Current
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The flow of electrons from the (-)
compartment to the (+) compartment
of the battery is called Current.
Electronic Circuits
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We can utilize this force between protons and
electrons.
LEDs light up when sufficient electrons pass
through them.
Create a circuit or “path” from the positive
terminal to the negative terminal through an
LED.
This forces the electrons to pass through the
LED to get to the (+) terminal of the battery.
“You have current through the circuit.”
Resistance
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Problem: When a wire or LED is
connected to a battery, all the electrons
in the (-) compartment try to go to the
(+) compartment all at once.
This results in more current than the
LED can handle and so the LED burns
out.
Resistance
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Solution: Use a resistor to slow the flow of
electrons.
Resistor allows electrons to flow through it,
but at a much slower rate.
In this way, the current or the flow of
electrons is at a rate that LED can handle.
The LED turns on but does not burn out.
Measurement Units
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Force between (+) terminal and (-) is
measured in voltage.
Current is measured in Amps.
Resistance is measured in Ohms.
Measurement Units
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Voltage can be measured with a
voltmeter.
Resistance can also be measured with a
ohm-meter.
Current can be measured with an ammeter.
A device that can measure all these
things is called a Multi-Meter.
Resistors
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Values of resistance is color coded on
resistor.
Black
0
Brown
1
Red
2
Orange
3
Yellow
4
Green
5
Blue
6
Violet
7
Gray
8
White
9
Calculating Resistance Values
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The color code can be read in the
following way:
(1st Color)(2nd Color) x 10^(3rd Color)
Example: Brown-Black-Red
(1)(0) x 10^(2)
= 10 x 100 = 1000 Ohms
Circuits
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A circuit diagram is called a schematic.
Example:
Components:
B – Battery
R – resistor
D – Light Emitting Diode
(LED)
The red arrow indicates the flow of
electrons in the positive convention*.
Here the resistor is in “series” with the LED.
(*This is reverse that of the true flow of electrons.
This convention stuck thanks to Ben Franklin who thought positive charged particles traveled
to the negative terminals.)
Demo and experiment
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Calculate resistor values.
Experiment.