section 1 dc circuits. chapter 1 fundamentals of electricity
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Section 1
DC Circuits
Chapter 1
Fundamentals of Electricity
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• Objectives– After completing this chapter, the student
should be able to:• Define matter, element, and molecule.
• List the parts of an atom.
• Define the valence shell of an atom.
• Identify the unit for measuring current.
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• Draw the symbol used to represent current flow in a circuit.
• Describe the difference among conductors and insulators and semiconductors.
• Define difference of potential, electromotive force, and voltage.
• Draw the symbol used to represent voltage.
• Identify the unit used to measure voltage.
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• Define resistance.
• Identify characteristics of resistance in a circuit.
• Identify the unit for measuring resistance.
• Draw the symbol used to represent resistance in a circuit.
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• Matter– Occupies space.
– Has weight.
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• Elements
– Basic building block of nature.
– Cannot be reduced to a simpler substance by chemical means.
– Over 100 known elements.
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• Parts of an atom– Nucleus
• Located at center of atom.
– Protons• Positively charged particles inside nucleus.
– Neutrons• Uncharged particles inside nucleus.
– Electrons• Negatively charged particles that orbit nucleus.
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• Atomic number– The number of protons in the nucleus of the
atom.
• Atomic weight– The mass of an atom.– Determined by the total number of protons and
neutrons in the nucleus.
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• Shell– Electrons orbit here.
– Concentric circles around nucleus.
– Filled in sequence.
• Valence Shell– The outermost shell.
• Valence– The number of electrons contained in the valence shell.
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• Conductors– Materials that
contain a large number of free electrons.
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• Insulators– Prevent the flow of
electricity.– Stabilized by
absorbing valence electrons.
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• Semiconductors– Can be altered to function as either a conductor
or insulator.
• Negative Ion– A negatively charged atom.
• Positive Ion– A positively charged atom.
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• Ionization– The process of gaining or losing electrons.– Significant in current flow.
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• Current– Movement of electrons from negatively
charged atoms to positively charged atoms.– Represented as I.
• Coulomb– 6.24 x 1018 electrons.– Represented as C.
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• Ampere– One coulomb moving past a single point in one
second.– Named for French physicist André Marie
Ampère. – Current measured in amperes.
– Represented by A.
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• Potential– The ability of the source to perform electrical
work.
• Difference of Potential– Causes electrons to move or flow in a circuit.– Referred to as electromotive force (emf) or
voltage.
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• Voltage– The force that moves the electrons in the
circuit.– The pressure or pump that moves electrons.– Represented by E.– Unit of measure called the volt.
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• Resistance– Opposition to the flow of electrons.– Degree of resistance depends on size, shape,
or temperature.– Measured in Ohms.
• Named for Georg Simon Ohm
– Represented by Greek letter Omega ().
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• Conductors– Low resistance to current flow.– Many free electrons.
• Insulators– High resistance to current flow.– Few free electrons.
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• In Summary– Matter– Elements– Atoms
• Nucleus• Protons• Neutrons• Electrons
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– Atomic Number– Atomic Weight– Shell
• Valence Shell– Valence
– Ionization– Current– Coulomb
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– Ampere– Electric current– Potential or electromotive force
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