Electrical Theory
Electrical Theory The
elements that comprise all matter are composed of atoms. As we learned in the
previous lesson "Atoms & Ions" we know that all atoms are
composed of three basic particles: protons, neutrons and electrons. These are
the building blocks of Electroneurodiagnostics. Each element possesses unique
characteristics and a basic understanding of them and electrical theory with
associated terminology is essential for the medical clinician performing
Neurodiagnostics. Understanding the concepts is fundamental in this
discipline as we are not just reading the bodies electrical potential, we are
introducing electricity into the body in order to do so. Voltage - A difference in
electric potential existing between two charged bodies. Electrical equivilant
of pressure. Also known as electromotive force or EMF. Voltage is the term used
to describe the electrical "pressure" or difference of potential.
Just as water pressure is the force in physics that pushes water through a
pipe, Voltage is the physical force which pushes electrons through a wire. In
the same sense, electrical pressure - just as water pressure pushes water
through a pipe. Voltage, causes current to flow through a wire. Voltage has
several other names. It is sometimes called potential difference. The unit of measurement for voltage is the volt
and it is measured by a voltmeter. You may run into KiloVolt s (Thousand Volts),
MilliVolt s (1 Thousandth of a Volt), or even MicroVolt s (1 Millionth of a
Volt).
The problem with discussing voltage is that it is difficult to talk about it, without discussing and resistance in the same breath. The three are almost inseparable, as you will soon come to see. CURRENT - The liquid like movement of free electrons within a conductor. Water has current. Electricity has current. Water has current only when the river flows. If it is standing water, such as in a pond, it does not flow, and therefore has no current. Electricity only has current when it is on the move.
Current is measured in amperes, using an ammeter, typically discussed as MilliApere ( 1 thousandth of an Ampere ) s or MicroAmpere ( 1 millionth of an Ampere ) s. Quite often, for the sake of quick speech and quicker typing, it is shortened to just 'Amps or MilliAmps. CONDUCTORS - Because of the distribution of electrons in the in an atom, some elements will allow electrical current to flow easier than others. Materials which easily allow the flow of electric current are called conductors. Conductors do not hold tightly to the electrons in their valence ring and are said to have a large number of free electrons. Some examples of good conductors are Gold, Silver, Copper, Aluminum, Zinc, and Carbon. INSULATORS - Other elements do not allow electrical current to flow easily, and these are called insulators. Insulators tend to hold tightly to the electrons in their valence ring and do not want to share with other atoms. Some examples of good insulators are Quartz, Mica, Teflon, Polystyrene, and Water. RESISTANCE - If water is moving through a hose, we say that it has flow.
If we restrict the flow, by pinching the hose, we are causing friction at the point of restriction. This friction can be said, is resistance to the flow of the water.
Electricity, according to Benjamin Franklin, acts like a fluid. It flows and has a measurable Current. We can restrict its flow by adding electrical friction. We say that the restriction of electrical flow is called resistance and that a device which causes such resistance is called a resister. All materials, even the very best conductors demonstrate a certain amount of resistance to electron flow.
In order to compare the resistance of various materials, we need to have some standard unit of measurement. The unit of measurement for resistance is called the Ohms and is indicated by the Greek letter Omega (Ω).
One Ω is defined as the amount of resistance that a 1000 foot piece of #10 copper wire has. A 3000 foot piece of #10 copper wire would have 3 Ohms of resistance. A 500 foot piece of #10 copper wire would exhibit 1/2 an Ohm, etc. Although Ohm is the basic unit, KiloOhm and MegOhm are frequently used. 1 KiloOhm (K Ω) is equal to 1 thousand Ω. 1 MegOhm (M &Omega) is equal to 1 million Ω.
There are 4 factors that determine the resistance of a material:
(1) Type of Material The resistance of various types of materials are different. For instance, copper is a better conductor of electricity than gold, and therefore has less resistance. (2) Length
The resistance of a material is directly proportional to its length. The longer the material is, the more resistance it has. This is because the electrons must flow through more material, and therefore meets more friction over the entire distance. (3) Cross Sectional Area
The resistance of a material is inversely proportional to the cross sectional area of the material. This means that the thicker the substance is across, the lower the resistance. This is because the larger the cross sectional area is, the less friction there is over a given length. (Picture in your mind, if you will, that a fire hose will pass more water than a garden hose, because the wider the pipe, the less resistance it has). (4) Temperature
In various types of materials, resistance can vary inversely or directly with the temperature. This is because of the chemical properties of the material. In Carbon, for instance, the resistance decreases as the temperature rises. So we say it varies inversely. In copper, however, the opposite is true, with the rise in temperature, we have a rise in the resistance. AC-DC In the case of a battery, electricity flows in one direction, from positive to negative. Everything is straightforward. In the case of a generator, however, things get a bit more complicated. It is possible to generate electricity by spinning a coil within a magnetic field. The coil is in constant motion within the magnetic field, and thus is transformed into electricity via the magnets. The electricity exits by way of the brushes and slip rings, but it is not exactly like the electricity which is produced by a battery.
DC - If we look at the current leaving the battery, it is constantly moving in the same direction. We call this direct current. But if we attach a generator instead of a battery in the same circuit, we notice a major change. The meter would swing back and forth from negative to positive.
This seems strange until we examine what is going on inside the generator. AC- As the wire coil rotates, it first passes the north pole of the magnet, producing an electric current flowing in a given direction. As the coil continues in its circular path, it passes the north pole, moving toward the south. As it approaches the south pole, the electric current begins to flow in the opposite direction from which it was originally moving. It continues to move in this direction until, once again, it approaches the north pole. We say, then that the electrical current is alternating between positive and negative. We call this type of current alternating current. OHMS LAW - Around 1840, German physicist Georg Ohm noted that there was a distinct mathematical relationship between Voltage, current and resistance. He then wrote the basis for what we now call ohm’s law. Ohm's Law states that Voltage (in Volts) is equal to the product of the current flowing through a resistance within a circuit. In other words... Voltage = Current times Resistance.
While we measure Voltage in Volts, we often use the letter E to represent Voltage. This is because another word for Voltage is simply E for electromotive. Also, we use the letter I to represent current. So that our formula becomes: E=IxR So what does this mean? Simply put, if we have a resistance of 10 Ohms (R=10), and a current of 10 Amps(I=10), we will have a Voltage of 100 Volts, because 10*10=100 (E=100).
Ohms law can also be stated two other ways. By using basic algebra, we can turn the formula around to make it say: I=E/R and R=E/I Coulomb's law is the electrostatic interaction between electrically charged particles. It was first published in 1785 by French physicist Charles Augustin de Coulomb and was essential to the development of the theory of electromagnetism.This law states that "The force of attraction or repulsion between two point charges is directly proportional to the product of magnitude of each charge and inversely proportional to the square of distance between them" Coulomb's law has been tested heavily and all observations are consistent with the law. ELECTRICAL INTERFERENCE - Electromagnetic interference (or EMI, also called radio frequency interference or RFI when in high frequency or radio frequency) is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. These effects can range from a simple degradation of data to a total loss of data. The source may be any object, artificial or natural, that carries rapidly changing electrical currents, such as an electrical circuit, the Sun or the Northern Lights. EMI can be intentionally used for radio jamming, as in some forms of electronic warfare, or can occur unintentionally, as a result of spurious emissions for example through intermodulation products, and the like. It frequently affects the reception of AM radio in urban areas. It can also affect cell phone, FM radio and television reception, although to a lesser extent.
Bibliography: -electronicstheory.com -In -- Coulomb (1785a) Histoire de l’Académie Royale des Sciences, pages 569-577
The problem with discussing voltage is that it is difficult to talk about it, without discussing and resistance in the same breath. The three are almost inseparable, as you will soon come to see. CURRENT - The liquid like movement of free electrons within a conductor. Water has current. Electricity has current. Water has current only when the river flows. If it is standing water, such as in a pond, it does not flow, and therefore has no current. Electricity only has current when it is on the move.
Current is measured in amperes, using an ammeter, typically discussed as MilliApere ( 1 thousandth of an Ampere ) s or MicroAmpere ( 1 millionth of an Ampere ) s. Quite often, for the sake of quick speech and quicker typing, it is shortened to just 'Amps or MilliAmps. CONDUCTORS - Because of the distribution of electrons in the in an atom, some elements will allow electrical current to flow easier than others. Materials which easily allow the flow of electric current are called conductors. Conductors do not hold tightly to the electrons in their valence ring and are said to have a large number of free electrons. Some examples of good conductors are Gold, Silver, Copper, Aluminum, Zinc, and Carbon. INSULATORS - Other elements do not allow electrical current to flow easily, and these are called insulators. Insulators tend to hold tightly to the electrons in their valence ring and do not want to share with other atoms. Some examples of good insulators are Quartz, Mica, Teflon, Polystyrene, and Water. RESISTANCE - If water is moving through a hose, we say that it has flow.
If we restrict the flow, by pinching the hose, we are causing friction at the point of restriction. This friction can be said, is resistance to the flow of the water.
Electricity, according to Benjamin Franklin, acts like a fluid. It flows and has a measurable Current. We can restrict its flow by adding electrical friction. We say that the restriction of electrical flow is called resistance and that a device which causes such resistance is called a resister. All materials, even the very best conductors demonstrate a certain amount of resistance to electron flow.
In order to compare the resistance of various materials, we need to have some standard unit of measurement. The unit of measurement for resistance is called the Ohms and is indicated by the Greek letter Omega (Ω).
One Ω is defined as the amount of resistance that a 1000 foot piece of #10 copper wire has. A 3000 foot piece of #10 copper wire would have 3 Ohms of resistance. A 500 foot piece of #10 copper wire would exhibit 1/2 an Ohm, etc. Although Ohm is the basic unit, KiloOhm and MegOhm are frequently used. 1 KiloOhm (K Ω) is equal to 1 thousand Ω. 1 MegOhm (M &Omega) is equal to 1 million Ω.
There are 4 factors that determine the resistance of a material:
(1) Type of Material The resistance of various types of materials are different. For instance, copper is a better conductor of electricity than gold, and therefore has less resistance. (2) Length
The resistance of a material is directly proportional to its length. The longer the material is, the more resistance it has. This is because the electrons must flow through more material, and therefore meets more friction over the entire distance. (3) Cross Sectional Area
The resistance of a material is inversely proportional to the cross sectional area of the material. This means that the thicker the substance is across, the lower the resistance. This is because the larger the cross sectional area is, the less friction there is over a given length. (Picture in your mind, if you will, that a fire hose will pass more water than a garden hose, because the wider the pipe, the less resistance it has). (4) Temperature
In various types of materials, resistance can vary inversely or directly with the temperature. This is because of the chemical properties of the material. In Carbon, for instance, the resistance decreases as the temperature rises. So we say it varies inversely. In copper, however, the opposite is true, with the rise in temperature, we have a rise in the resistance. AC-DC In the case of a battery, electricity flows in one direction, from positive to negative. Everything is straightforward. In the case of a generator, however, things get a bit more complicated. It is possible to generate electricity by spinning a coil within a magnetic field. The coil is in constant motion within the magnetic field, and thus is transformed into electricity via the magnets. The electricity exits by way of the brushes and slip rings, but it is not exactly like the electricity which is produced by a battery.
DC - If we look at the current leaving the battery, it is constantly moving in the same direction. We call this direct current. But if we attach a generator instead of a battery in the same circuit, we notice a major change. The meter would swing back and forth from negative to positive.
This seems strange until we examine what is going on inside the generator. AC- As the wire coil rotates, it first passes the north pole of the magnet, producing an electric current flowing in a given direction. As the coil continues in its circular path, it passes the north pole, moving toward the south. As it approaches the south pole, the electric current begins to flow in the opposite direction from which it was originally moving. It continues to move in this direction until, once again, it approaches the north pole. We say, then that the electrical current is alternating between positive and negative. We call this type of current alternating current. OHMS LAW - Around 1840, German physicist Georg Ohm noted that there was a distinct mathematical relationship between Voltage, current and resistance. He then wrote the basis for what we now call ohm’s law. Ohm's Law states that Voltage (in Volts) is equal to the product of the current flowing through a resistance within a circuit. In other words... Voltage = Current times Resistance.
While we measure Voltage in Volts, we often use the letter E to represent Voltage. This is because another word for Voltage is simply E for electromotive. Also, we use the letter I to represent current. So that our formula becomes: E=IxR So what does this mean? Simply put, if we have a resistance of 10 Ohms (R=10), and a current of 10 Amps(I=10), we will have a Voltage of 100 Volts, because 10*10=100 (E=100).
Ohms law can also be stated two other ways. By using basic algebra, we can turn the formula around to make it say: I=E/R and R=E/I Coulomb's law is the electrostatic interaction between electrically charged particles. It was first published in 1785 by French physicist Charles Augustin de Coulomb and was essential to the development of the theory of electromagnetism.This law states that "The force of attraction or repulsion between two point charges is directly proportional to the product of magnitude of each charge and inversely proportional to the square of distance between them" Coulomb's law has been tested heavily and all observations are consistent with the law. ELECTRICAL INTERFERENCE - Electromagnetic interference (or EMI, also called radio frequency interference or RFI when in high frequency or radio frequency) is disturbance that affects an electrical circuit due to either electromagnetic induction or electromagnetic radiation emitted from an external source. The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit. These effects can range from a simple degradation of data to a total loss of data. The source may be any object, artificial or natural, that carries rapidly changing electrical currents, such as an electrical circuit, the Sun or the Northern Lights. EMI can be intentionally used for radio jamming, as in some forms of electronic warfare, or can occur unintentionally, as a result of spurious emissions for example through intermodulation products, and the like. It frequently affects the reception of AM radio in urban areas. It can also affect cell phone, FM radio and television reception, although to a lesser extent.
Bibliography: -electronicstheory.com -In -- Coulomb (1785a) Histoire de l’Académie Royale des Sciences, pages 569-577
