Current, Voltage and Resistance Electronic Training Course Slide# 1

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

Slide# 3 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# 4 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# 5 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 ) electrons flowing per second through the wire or 6,240,000,000,000,000,000 (6 quintillion two hundred forty quadrillion).

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

Slide# 8 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# 9 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# 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

Slide# 12 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# 13 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# 14 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# 15 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# 16 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# 17 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# 18 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# 19 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.

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 _____ througha 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 _____ througha 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 _____ througha 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 _____ througha 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 _____ througha 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 _____ througha 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 Current, Voltage & Resistance