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ElectricityElectricity
Topics Covered in Chapter 11-1: Negative and Positive Polarities
1-2: Electrons and Protons in the Atom1-3: Structure of the Atom
1-4: The Coulomb Unit of Electric Charge1-5: The Volt Unit of Potential Difference
Topics Covered in Chapter 1Topics Covered in Chapter 1 1-6: Charge in Motion Is Current 1-7: Resistance Is Opposition to Current 1-8: The Closed Circuit 1-9 The Direction of Current 1-10: Direct Current (DC) and Alternating Current (AC) 1-11: Sources of Electricity 1-12: The Digital Multimeter
1-1: Negative and Positive 1-1: Negative and Positive PolaritiesPolarities
Electrons and Protons: All the materials we know, including solids, liquids and
gases, contain two basic particles of electric charge: the electron and the proton.
The electron is the smallest particle of electric charge having the characteristic called negative polarity.
The proton is the smallest particle of electric charge having the characteristic called positive polarity.
1-1: Negative and Positive 1-1: Negative and Positive PolaritiesPolarities
The arrangement of electrons and protons in a substance determines its electrical characteristics.
When the number of protons and electrons in a substance are equal, they cancel each other out, making the substance electrically neutral.
1-1: Negative and Positive 1-1: Negative and Positive PolaritiesPolarities
To use the electrical forces associated with the negative and positive charges in matter, the electrons and protons must be separated.
Changing the balance of forces produces evidence of electricity.
1-1: Negative and Positive 1-1: Negative and Positive PolaritiesPolarities
Fig. 1-1: Positive and negative polarities for the voltage output of a typical battery.
1-2: Electrons and Protons in the 1-2: Electrons and Protons in the AtomAtom
When electrons in the outermost ring of an atom can move easily from one atom to the next in a material, the material is called a conductor. Examples of conductors include:
silver copper aluminum.
1-2: Electrons and Protons in the 1-2: Electrons and Protons in the AtomAtom
When electrons in the outermost ring of an atom do not move about easily, but instead stay in their orbits, the material is called an insulator. Examples of insulators include:
glass plastic rubber.
1-2: Electrons and Protons in the 1-2: Electrons and Protons in the AtomAtom
Semiconductors are materials that are neither good conductors nor good insulators. Examples of semiconductors include:
carbon silicon. germanium
1-3: Structure of the Atom1-3: Structure of the Atom Atomic Number
The atomic number of an element is the number of protons in the nucleus of the atom balanced by an equal number of orbiting electrons.
The number of electrons in orbit around the nucleus of a neutral atom is equal to the number of protons in the nucleus.
1-3: Structure of the Atom1-3: Structure of the Atom Orbital Rings
Electrons are contained in successive rings beyond the nucleus. The rings are called K, L, M, N, O, P, and Q, respectively.
Each ring has a maximum number of electrons for stability. They are:
K ring = 2 electrons.L ring = 8 electrons.M ring = 8 or 18 electrons.N ring = 8,18, or 32 electrons.
O ring = 8 or 18 electronsP ring = 8 or 18 electronsQ ring = 8 electrons
1-3: Structure of the Atom1-3: Structure of the Atom The maximum number of electrons in the outermost ring
is always 8.
The electron valence of an atom is the number of electrons in an incomplete outermost shell. The valence indicates how easily the atom can gain or lose electrons.
An atom’s nucleus contains neutrons as well as protons.
Neutrons have no net electric charge.
One Atom of Copper
K
K = 2(complete)
L
L = 8(complete)
MM = 18
(complete)
N = 1(incomplete)N
Atomic number = 29
1-3: Structure of the Atom1-3: Structure of the Atom
1-3: Structure of the Atom1-3: Structure of the AtomThe valence electron is weakly bound to the nucleus. This makes copper an excellent conductor.
29 protonsatomic number = 29
29 electrons(net charge = 0)
1 valence electron
29 protonsatomic number = 29
29 electrons(net charge = 0)
1 valence electron
1-4: The Coulomb Unit of Electric 1-4: The Coulomb Unit of Electric ChargeCharge
Most common applications of electricity require the charge of billions of electrons or protons.
1 coulomb (C) is equal to the quantity (Q) of 6.25 × 1018
electrons or protons.
The symbol for electric charge is Q or q, for quantity.
1-4: The Coulomb Unit of Electric 1-4: The Coulomb Unit of Electric ChargeCharge
Negative and Positive Polarities Charges of the same polarity tend to repel each other. Charges of opposite polarity tend to attract each other. Electrons tend to move toward protons because
electrons have a much smaller mass than protons. An electric charge can have either negative or positive
polarity. An object with more electrons than protons has a net negative charge (-Q) whereas an object with more protons than electrons has a net positive charge (+Q).
An object with an equal number of electrons and protons is considered electrically neutral (Q = 0C)
1-4: The Coulomb Unit of Electric 1-4: The Coulomb Unit of Electric ChargeCharge
1-4: The Coulomb Unit of Electric 1-4: The Coulomb Unit of Electric ChargeCharge
Charge of an Electron The charge of a single electron, or Qe, is 0.16 × 10−18 C. It is expressed
−Qe = 0.16 × 10−18 C (−Qe indicates the charge is negative.)
The charge of a single proton, QP, is also equal to 0.16 × 10−18 C .
However, its polarity is positive instead of negative.
1-5: The Volt Unit of Potential 1-5: The Volt Unit of Potential DifferenceDifference
Potential refers to the possibility of doing work. Any charge has the potential to do the work of moving
another charge, either by attraction or repulsion. Two unlike charges have a difference of potential. Potential difference is often abbreviated PD. The volt is the unit of potential difference. Potential difference is also called voltage.
1-5: The Volt Unit of Potential 1-5: The Volt Unit of Potential DifferenceDifference
The volt is a measure of the amount of work or energy needed to move an electric charge.
The metric unit of work or energy is the joule (J). One joule = 0.7376 ft·lbs.
The potential difference (or voltage) between two points equals 1 volt when 1 J of energy is expended in moving 1 C of charge between those two points. 1 V = 1 J / 1 C
1-5: The Volt Unit of Potential 1-5: The Volt Unit of Potential DifferenceDifference
Fig. 1-7: The amount of work required to move electrons between two charges depends on their difference of potential. This potential difference (PD) is equivalent for the examples in (a), (b), and (c).
1-6: Charge in Motion Is 1-6: Charge in Motion Is CurrentCurrent
The amount of current is dependent on the amount of voltage applied.
The greater the amount of applied voltage, the greater the number of free electrons that can be made to move, producing more charge in motion, and therefore a larger value of current.
Current can be defined as the rate of flow of electric charge. The unit of measure for electric current is the ampere (A).
1 A = 6.25 × 1018 electrons (1C) flowing past a given point each second, or 1A= 1C/s.
The letter symbol for current is I or i, for intensity.
1-7: Resistance Is 1-7: Resistance Is Opposition to CurrentOpposition to Current
Resistance is the opposition to the flow of current. A component manufactured to have a specific value of
resistance is called a resistor. Conductors, like copper or silver, have very low
resistance. Insulators, like glass and rubber, have very high
resistance. The unit of resistance is the ohm (Ω). The symbol for resistance is R.
1-7: Resistance Is 1-7: Resistance Is Opposition to CurrentOpposition to Current
1-8: The Closed Circuit1-8: The Closed Circuit A circuit can be defined as a path for current flow. Any
circuit has three key characteristics:1. There must be a source of potential difference
(voltage). Without voltage current cannot flow.2. There must be a complete path for current flow.3. The current path normally has resistance, either to
generate heat or limit the amount of current.
1-8: The Closed Circuit1-8: The Closed Circuit Open and Short Circuits
When a current path is broken (incomplete) the circuit is said to be open. The resistance of an open circuit is infinitely high. There is no current in an open circuit.
When the current path is closed but has little or no resistance, the result is a short circuit. Short circuits can result in too much current.
A closed circuit(current is flowing)
The purpose of theresistor is to limitcurrent (flow) or
1-9: Direction of the Current1-9: Direction of the Current With respect to the positive and negative terminals of
the voltage source, current has direction. When free electrons are considered as the moving
charges we call the direction of current electron flow. Electron flow is from the negative terminal of the voltage source through the external circuit back to the positive terminal.
Conventional current is considered as the motion of positive charges. Conventional current flows in the opposite direction from electron flow (positive to negative).
1-9: Direction of the Current1-9: Direction of the CurrentFig. 1-13: Direction of I in a closed
circuit, shown for electron flow and conventional current. The circuit works the same way no matter which direction you consider. (a) Electron flow indicated with dashed arrow in diagram. (b) Conventional current indicated with solid arrow. (c) Electron flow as in (a) but with reversed polarity of voltage source. (d) Conventional I as in (b) but reversed polarity for V.
1-10: Direct Current 1-10: Direct Current and Alternating Currentand Alternating Current
Direct current (dc) flows in only one direction.
Alternating current (ac) periodically reverses direction.
The unit for 1 cycle per second is the hertz (Hz). This unit describes the frequency of reversal of voltage polarity and current direction.
1-10: Direct Current1-10: Direct Currentand Alternating Currentand Alternating Current
Fig. 1-14: Steady dc voltage of fixed polarity, such as the output of a battery. Note the schematic symbol at left.
Fig. 1-15: Sine-wave ac voltage with alternating polarity, such as from an ac generator. Note the schematic symbol at left. The ac line voltage in your home has this waveform.