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