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Current, Voltage
and Resistance
Electronic Training Course
Slide# 1
Current, Voltage & Resistance
Electronic Current
In the previous presentation (The Atom) you
learned that everything is made of atoms and
that atoms have a positive nucleus with negative
electrons orbiting around it. Now you might
wonder, what does all this have to do with
electronics?
Well, as we will see, an electric current is nothing
more than the flow of millions and millions of
electrons through a wire or conductive material.
Slide# 2
Current, Voltage & Resistance
For example, if you connect a piece of wire between the positive and negative terminals
of a charged battery, electrons from the negative side will flow through the wire to the
positive side of the battery.
On the negative side of a charged battery there are millions and millions of electrons
that broke loose from their atoms through a chemical reaction and accumulated on the
negative side.
Slide# 3
Current, Voltage & Resistance
On the positive side of the battery there are millions and millions of atoms that lost
electrons and therefore they lost their neutrality and have a positive charge. The
electrons, attracted by the positive ions, travel through the wire from the negative side
of the battery to the positive side, this flow of electrons constitutes an electric current.
Slide# 4
Current, Voltage & Resistance
The amount of current that flows through a wire is measured in amperes, also called
Amps. The Ampere indicates how many electrons flow through the wire per second.
A current of 1 Ampere constitutes 6.24 E18 (6.24 x 1018) electrons flowing per second
through the wire or 6,240,000,000,000,000,000 (6 quintillion two hundred forty
quadrillion).
Slide# 5
Current, Voltage & Resistance
What is Voltage?
Slide# 6
Current, Voltage & Resistance
What is Voltage?
Voltage is the force or the electric pressure that
causes the current to flow through a wire or
conductive material. The voltage is produced by
the accumulation of positive and negative
charges on the terminals or poles of a battery or
electric generator.
Slide# 7
Current, Voltage & Resistance
As you have seen before, the accumulation of electrons on one side of the battery and
positive atoms on the other side constitutes a difference of potential or voltage across
the terminals or poles of a battery.
This difference of potential or voltage across the terminals of a battery will cause an
electric current to flow through a wire or conductor connected across the terminals.
Slide# 8
Current, Voltage & Resistance
When a battery is totally discharged, all the electrons that were in excess on the
negative side have migrated to the positive side neutralizing the positive atoms on the
positive side. When this happens the battery does not have any voltage (0 volts) across
its terminals and it does not have the capacity of producing any electric current when a
wire is connected across its terminals.
Slide# 9
Current, Voltage & Resistance
What is Resistance?
Slide# 10
Current, Voltage & Resistance
What is Resistance?
Resistance is the opposition that materials present
to the flow of current (opposition to current flow).
Slide# 11
Current, Voltage & Resistance
According to their resistance, materials can be classified into conductors, insulators or
semiconductors. For example, the copper wire inside a cable is a conductor while the
plastic insulation of the cable is an insulator. Semiconductor materials such as
germanium and silicon are used to manufacture integrated circuits, transistors, diodes,
and other electronic components.
Slide# 12
Current, Voltage & Resistance
Some materials like copper, aluminum, gold and other metals have the ability of
allowing electrons to flow through them. They are good conductors of electricity
because some of the electrons from their atoms left the outer orbits and became free
to wander from atom to atom through the whole material.
Good conductors of electricity have millions and millions of free electrons constantly
wandering from atom to atom even when no voltage is applied to them.
Slide# 13
Current, Voltage & Resistance
This movement of free electrons in a conductor does not produce an electric current
because it is erratic (in any direction) and not in a specific direction which occurs when
a voltage is applied across the conductor.
Slide# 14
Current, Voltage & Resistance
When voltage is applied across a conductor all the free electrons start moving toward
the positive side of the voltage source. This movement of free electrons in one specific
direction constitutes an electric current.
When a wire is connected across the terminals of a battery electrons start flowing
through the wire. For every electron introduced by the battery into the wire from the
negative side, one electron leaves the wire toward the positive side of the battery.
Therefore the amount of free electrons in the wire is always the same.
Slide# 15
Current, Voltage & Resistance
There are some materials that do not have free electrons wandering from atom to atom
in their atomic structure. This means that each electron is on its respective orbit and not
going from one atom to another. Materials with these characteristics like glass,
porcelain and rubber do not allow electric current to flow through them. They are called
insulators.
Slide# 16
Current, Voltage & Resistance
There are materials such as silicon and germanium that are neither good conductors or
good insulators of electricity. They are between these two categories and are called
semiconductors. As you will learn in future courses semiconductors perform a very
important role in electronics, as we have said earlier they are used to manufacture
integrated circuits, transistors, diodes, etc.
Slide# 17
Current, Voltage & Resistance
Good conductors of electricity such as copper, aluminum and gold have a very low
resistance. Insulators, such as glass, porcelain and rubber have a very high resistance.
Semiconductors have a medium resistance, neither high or low.
Resistance is measured in ohms. A short piece of copper wire has less than 1 ohm of
resistance on the other hand a short piece of glass might have a resistance in millions of
ohms.
Slide# 18
Current, Voltage & Resistance
There are certain types of electronic components called resistors which are used to limit
the current in circuits. Each resistor has a specific resistance. The value of resistance of
each resistor is specified with marks on its case using a color code.
Slide# 19
Current, Voltage & Resistance
Review
Electric current is the flow of electrons through a conductor.
The current flows from the negative side of the battery
toward the positive side. Current is measured in Amperes.
Voltage is the force or electric pressure that produces the
electric current. If there is no voltage there is no current.
Voltage is measured in Volts.
Resistance is the opposition that materials present to the
flow of current through them. According to their resistance
materials can be classified as: conductors, insulators, or
semiconductors.
Slide# 20
Current, Voltage & Resistance
Review
Conductors such as copper, aluminum and gold allow
electric current to flow through them. Conductors have
millions and millions of free electrons in their atomic
structure.
Free electrons in a conductor start moving in one direction
as soon as voltage is applied to the conductor. The
movement of free electrons in one specific direction
constitutes an electric current.
Insulators such as glass, porcelain and rubber do not allow
current to flow through them. They have none or very few
free electrons in their atomic structure.
Slide# 21
Current, Voltage & Resistance
Review
Semiconductors are neither good conductors or insulators.
Semiconductor materials such as germanium and silicon are
used to manufacture electronic components such as
transistors, diodes, and integrated circuits.
Resistance is measured in ohms (Ω). Good conductors have
low resistance and good insulators have high resistance. A
small piece of copper wire has less than one ohm of
resistance. On the other hand a small piece of glass has
millions of ohms of resistance. Resistors are used in electric
and electronic circuits to limit the current. Each resistor has
a specific resistance which is noted by a color code.
Slide# 22
Current, Voltage & Resistance
Test
1. Electric current is the flow of _____ through a conductor.
2. Electric current flows from the _____ side of a
battery or voltage source.
3. The unit Ampere is used to express what value?
4. Electric pressure that allows current flow is _____.
5. Voltage is measured in _____.
Slide# 23
Current, Voltage & Resistance
Test
1. Electric current is the flow of _____ through a conductor.
Electrons
2. Electric current flows from the _____ side of a
battery or voltage source.
3. The unit Ampere is used to express what value?
4. Electric pressure that allows current flow is _____.
5. Voltage is measured in _____.
Slide# 24
Current, Voltage & Resistance
Test
1. Electric current is the flow of _____ through a conductor.
Electrons
2. Electric current flows from the _____ side of a
battery or voltage source.
Negative to positive
3. The unit Ampere is used to express what value?
4. Electric pressure that allows current flow is _____.
5. Voltage is measured in _____.
Slide# 25
Current, Voltage & Resistance
Test
1. Electric current is the flow of _____ through a conductor.
Electrons
2. Electric current flows from the _____ side of a
battery or voltage source.
Negative to positive
3. The unit Ampere is used to express what value?
Current
4. Electric pressure that allows current flow is _____.
5. Voltage is measured in _____.
Slide# 26
Current, Voltage & Resistance
Test
1. Electric current is the flow of _____ through a conductor.
Electrons
2. Electric current flows from the _____ side of a
battery or voltage source.
Negative to positive
3. The unit Ampere is used to express what value?
Current
4. Electric pressure that allows current flow is _____.
Voltage
5. Voltage is measured in _____.
Slide# 27
Current, Voltage & Resistance
Test
1. Electric current is the flow of _____ through a conductor.
Electrons
2. Electric current flows from the _____ side of a
battery or voltage source.
Negative to positive
3. The unit Ampere is used to express what value?
Current
4. Electric pressure that allows current flow is _____.
Voltage
5. Voltage is measured in _____.
Volts
Slide# 28
Current, Voltage & Resistance
Test
6. The opposition to the flow current is _____.
7. According to their _____ materials can be classified as:
conductors, insulators or semiconductors.
8. Resistance is measured in _____.
9. Good electric conductors have a _____ resistance.
10. Materials with many _____ in their atomic structure are
good conductors of electricity.
Slide# 29
Current, Voltage & Resistance
Test
6. The opposition to the flow current is _____.
Resistance
7. According to their _____ materials can be classified as:
conductors, insulators or semiconductors.
8. Resistance is measured in _____.
9. Good electric conductors have a _____ resistance.
10. Materials with many _____ in their atomic structure are
good conductors of electricity.
Slide# 30
Current, Voltage & Resistance
Test
6. The opposition to the flow current is _____.
Resistance
7. According to their _____ materials can be classified as:
conductors, insulators or semiconductors.
Resistance
8. Resistance is measured in _____.
9. Good electric conductors have a _____ resistance.
10. Materials with many _____ in their atomic structure are
good conductors of electricity.
Slide# 31
Current, Voltage & Resistance
Test
6. The opposition to the flow current is _____.
Resistance
7. According to their _____ materials can be classified as:
conductors, insulators or semiconductors.
Resistance
8. Resistance is measured in _____.
Ohms
9. Good electric conductors have a _____ resistance.
10. Materials with many _____ in their atomic structure are
good conductors of electricity.
Slide# 32
Current, Voltage & Resistance
Test
6. The opposition to the flow current is _____.
Resistance
7. According to their _____ materials can be classified as:
conductors, insulators or semiconductors.
Resistance
8. Resistance is measured in _____.
Ohms
9. Good electric conductors have a _____ resistance.
Low
10. Materials with many _____ in their atomic structure are
good conductors of electricity.
Slide# 33
Current, Voltage & Resistance
Test
6. The opposition to the flow current is _____.
Resistance
7. According to their _____ materials can be classified as:
conductors, insulators or semiconductors.
Resistance
8. Resistance is measured in _____.
Ohms
9. Good electric conductors have a _____ resistance.
Low
10. Materials with many _____ in their atomic structure are
good conductors of electricity.
Free Electrons
Slide# 34