Electricity
Negative and Positive Polarities
All materials, including solids, liquids, and gasses, contain two basic particles of electric charge: the electron and the proton. The electron has a negative polarity, and the proton has a positive polarity. A material in electrically balanced or neutral, when the number of electrons equals the number of protons. A battery has positive and negative terminals marked to emphasize the two opposite polarities.!(battery with terminals marked)
Electrons and Protons in the Atom
An atom is the smallest unit of matter and the smallest unit of an element. Electrons and protons make up an atom. Protons are 1840 times heavier than electrons. The total number of electrons in the outside ring must equal the number of protons in the nucleus in a neutral atom. The carbon atom has one electron in its outermost (4th) orbital shell.!(bohr carbon atom w/ KLMN shells)
The distribution of electrons in the orbital rings determines the atom's electrical stability. Electrons that flow freely from one atom to another are called free electrons. Their movement is random. When voltage is applied, all free electrons move in the same direction. When electrons can move easily from atom to atom in in a material, it is a conductor. A material with atoms in which the electrons tend to stay in their own orbitals is an insulator. Semiconductors conduct less than the metal conductors but more than the insulators. For instance glass and rubber are both insulators, copper is a conductor, and silicon is a semiconductor. I insulators are often called dielectrics, meaning that they can store electric charge. An element is a substance that cannot be broken down any further by chemical action. Copper, Hydrogen, and Silver are all examples of elements. A molecule is a group of two or more atoms. A compound consists of two or or more elements. An example of a compound is H2O (water).
Structure of the atom
The orbit for the planetary electrons are also called shells or energy levels. The atomic number gives the number of protons or electrons required in the atom for each element. The atomic number of the hydrogen atom is 1. The atomic number of the copper atom atom is 29. The planetary electrons are in successive shells. The K shell can hold a maximum of 2 electrons. The N shell can hold an maximum of 8, 18 or 32 electrons. The P shell can hold a maximum of 8 or 18 electrons. Each shell will fill to its maximum number before the next shell will start to fill. The element Aluminium will have three shells and 13 electrons. Inert gasses have the correct amount of valance electrons so they cannot gain or loose any more. The electron valence is the number of electrons in a complete outermost shell. The positive valance is the number of electrons in an outermost shell. The negative valance is the number of electrons needed to complete an outer shell. Aluminum needs 5 more electrons in the outer shell to be complete and stable. All the shells accept K are divided into sub shells. Electrons in one sub-shell may have electrical orbits. Other electrons in the same main shell may have circular orbits. A stable nucleus contains protons and neutrons. Electrons are electrically negative. Protons are electrically positive. Neutrons are electrically neutral.
The Coulomb Unit of Electrically Charged
An example of static electricity is if you were to walk across a wool rug. When this happens your body becomes charged with an excess of electrons. This is static electricity because the electrons or protons are not in motion. If you were now to touch a door knob, the excess electrons would travel to the metal and giver you a shock. The coulomb it the basic unit of electric charge. It is represented by 6.25 x 10^18 electrons or protons. since an electron is too small for use, we apply the coulomb as the basic unit of electric charge. The symbol for coulomb is Q. The Q is the basic unit of charge. For example, we write, "Q = 5 C' instead of writing "the charge is 5 coulomb".
Historically, negative polarity has been assigned to static charge produced on rubber and other resinous materials. Polarity refers to the static charge produced on glass and other vitreous materials. If two small charged bodies of light weight are placed next to each other, one can be attracted to the other when the charges have opposite polarity. Opposite charges attract and like charges repel. An electric charge must have either negative or positive polarity, labeled -Q or +Q. For example, if a neutral dielectric has added to it 25 x 10^18 electrons, its charge in columns is 3. Therefor Q = SC.
The quantity of any charge is measured by its force of attraction or repulsion. The charge of one electron is: -Qe = 0.16 x 10^-18 C. The charge of one proton is +Qp = 0.16 x 10^-18 C. Notice that the values of -Qe and +Qp are the same. The difference is the polarity. The electric field of a charged particle is a circle. However, unlike many physical forces, electrical charge is physical force. The resulting physical affects prove the field is there.
Historically, negative polarity has been assigned to static charge produced on rubber and other resinous materials. Polarity refers to the static charge produced on glass and other vitreous materials. If two small charged bodies of light weight are placed next to each other, one can be attracted to the other when the charges have opposite polarity. Opposite charges attract and like charges repel. An electric charge must have either negative or positive polarity, labeled -Q or +Q. For example, if a neutral dielectric has added to it 25 x 10^18 electrons, its charge in columns is 3. Therefor Q = SC.
The quantity of any charge is measured by its force of attraction or repulsion. The charge of one electron is: -Qe = 0.16 x 10^-18 C. The charge of one proton is +Qp = 0.16 x 10^-18 C. Notice that the values of -Qe and +Qp are the same. The difference is the polarity. The electric field of a charged particle is a circle. However, unlike many physical forces, electrical charge is physical force. The resulting physical affects prove the field is there.
The Volt Unit of Potential Difference
Potential refers to the possibility of doing work. When we consider two unlike charges, they have a difference of potential. The potential difference between a particle with a charge of +1C and a particle with a charge of -2C is 3C.
!(two particles with charges as shown above)
The volt is a measure of the work needed to move an electric charge. The current in some liquids and gasses is a result of the motion of positive charge.
!(liquid in container with labeled +/- terminals and an arrow from + to -)
In metal conductors and solid materials the direction of electron flow is from the negative terminal of the voltage source, through the external circuit, and returning to the positive source of the terminal.
!(simple circuit with a resistor and a battery(labeled applied voltage))
In P-type semiconductors there is a deficiency of electrons in the bonds between the atoms. This causes a hole charge. The polarity of a hole charge is positive. An ion charge may be either positive or negative. When any current flows, it has an associated magnetic field. Iron filings will line up in a circular pattern and make the invisible magnetic field visible.
Resistance is Opposition to Current
Resistance is the opposition that a material gives to current. The symbol for resistance is R or r. In electronics, the amount of resistance is stated in ohms, the base unit of resistance. The symbol for ohm is Ω. A resistance that develops 0.24 calories of heat when 1 ampere of current flows through it for 1 second has 1 ohm of opposition.
Low Resistance: A good conductor like copper wire can have a resistance of 0.01 Ω for a 1 foot length.
Medium Resistance: The heating element in a 600-W 120-V toaster has a resistance of 24 Ω.
High Resistance: The insulation surrounding the copper conductors in an extension cord has several million ohms of resistance.
The opposite of resistance is conductance. Resistance and conductance have a reciprocal, or reverse, relationship. The symbol for conductance is G and the unit is Siemens.
The Closed Circuit
A circuit can be defined as a path for current to flow through. The graphic bellow shows how a circuit is used to light the bulb in a flashlight.
!(flashlight x-ray)
Bellow is the schematic of the previous circuit.
!(flashlight schematic)
Components in a circuit are represented by symbols.
1 volt will move 1 coulomb between two points to produce one Joule of work.
Charge in Motion is Current
When the potential difference between two charges forces a third charge to move, the motion is an electric current. To produce a current, charge must be moved by a potential difference. Assume a copper wire is not connected to any voltage source so there is no potential difference across the wire. The current is 0. However, if you connect the wire to a voltage source, the potential difference would create a current. A large amount of moving charges means a higher value of current. Two connections to two points are needed to produce the current. Current is the movement of charge. When the charge moves at the rate of 6.25 x 10^18 free electrons per second past a certain point, the value of the current is 1 Ampere. 1 Ampere (A) is equal to 1 C of charge per second. The symbol for current is i.
Current is defined by this equation: I = intensity or Current = i. The practical units which measure these quantities are: 1A = 1C / 1S. The definition of current can also be used to consider the charge as equal to the product of the current multiplied by the time. The formula for charge is Q = I x T.
Current in metal conductors like copper wire has a negative polarity because the direction of the current is toward the positive end. Free electrons in metal conductors like copper wire flow towards the positive end of the battery.
!(battery with arrow from neg to pos)
Three things that an electric circuit must have are potential difference, a complete path for current to flow, and resistance. Current moves through the circuit but potential difference does not move. You can measure current by the intensity of the electron flow past any one point in the circuit. Voltage is the potential difference between two points, so it must be measured form two points. The battery keeps the current flowing by maintaining the potential difference across the circuit. The battery is the voltage source for the circuit.
!(battery connected to circuit)
The part of the circuit that is connected to the voltage source is the load resistance. The current that flows through the load resistance that is called load current. When a circuit has a resistance that is near zero, the result is usually a short circuit. When any part of the path is broken, the circuit is open because there is no continuity in the conducting path. For example, when the resistance in a light bulb wears down, the filament will get too hot and short circuit. The circuit is now open because there is no continuity in the conductive path.
Direction of Current
Just as a voltage source has polarity, the current has a direction. The direction of electron drift is from the negative side of the voltage source to the positive side. Current can also be understood as the movement of positive charges called conventional current. Notice that the current moves on the opposite direction from the electron drift.
!(battery with wires and arrows (pos to neg) leading to a box with + charges moving towards the negative side)
Remember, the electrons move, the protons do not move. One way of understanding this concept is by the hole charge. An example of positive charges in motion for conventional current is the current of the hole charges in P type semiconductors.
Direct Current (DC) and Alternating Current (AC)
The two types of current are direct current (DC) and alternating current (AC). A DC circuit has a fixed polarity and the flow of the charge is in one direction. An AC circuit alternates in polarity, and the current alternates.
!(oscilloscope graphs of direct and alternating current)
Sources of Electricity
Examples of sources of electricity are: static electricity, conversion of chemicals, electromagnetism, photoelectricity, and thermal emission.
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