Section 1 DC Circuits

Chapter 1 Fundamentals of Electricity

3 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.

4 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.

5 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.

6 Matter –Occupies space. –Has weight.

7 Elements –Basic building block of nature. –Cannot be reduced to a simpler substance by chemical means. –Over 100 known elements.

8 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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10 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.

11 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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13 Conductors –Materials that contain a large number of free electrons.

14 Insulators –Prevent the flow of electricity. –Stabilized by absorbing valence electrons.

15 Semiconductors –Can be altered to function as either a conductor or insulator. Negative Ion –A negatively charged atom. Positive Ion –A positively charged atom.

16 Ionization –The process of gaining or losing electrons. –Significant in current flow.

17 Current –Movement of electrons from negatively charged atoms to positively charged atoms. –Represented as I. Coulomb –6.24 x electrons. –Represented as C.

18 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.

19 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.

20 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.

21 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 (  ).

22 Conductors –Low resistance to current flow. –Many free electrons. Insulators –High resistance to current flow. –Few free electrons.

23 In Summary –Matter –Elements –Atoms Nucleus Protons Neutrons Electrons

24 –Atomic Number –Atomic Weight –Shell Valence Shell –Valence –Ionization –Current –Coulomb

25 –Ampere –Electric current –Potential or electromotive force