Voltage, Current and Resistance The Bohr atom Bohr. (nucleus) (protons)t (neutrons)..,.,. Electron Proton Neutron
A neutral Si atom is shown. There are 4 electrons in the valence shell. Is Si a conductor, insulator, or semiconductor? Semiconductor
Q 18 6.2510 /C How many coulomb of charge do 93.810 16 electrons represent? Electrical charge : (F).,.,. F Q1Q k r 2 2 _ Voltage. When force is applied over a distance, work is done. Work done in moving a charge against the electric e - field leads to the definition of voltage: Voltage is thework per charge done against the electric field.
Voltage. W V Q 1 (volt) 1 1, (). Voltage Voltage. e -,, Zinc. (anode) Cu-Zn Zn 2 e- Copper (cathode) - Zn 2e Cu 2-2e ZnSO 4 solution Porous barrier CuSO 4 solution Cu. IV :.,. I V
Current (I)(t) ( Q).,. Q I t Ampere : I = ( : A) Q = ( :C) t = ( : ) 1A 11C. A,. What is the current if 2 C passes a point in 5 s? 0.4 A Current Source. IV : I V
Ohm :. 1 1V 1A..( : simens, mho) 1 G R,,. Color bands Resistance material (carbon composition) Insulation coating Leads Resistance color-code,, 3: band 1 st digit band 2 nd digit *band ( 0 ) band Color Digit Multiplier Tolerance Black Brown Red Orange Yellow Green Blue Violet Gray White Gold Silver 0 1 2 3 4 5 6 7 8 9 5% 10% No band 20% 10 0 10 1 10 2 10 3 10 4 10 5 10 6 10 7 10 8 10 9 10-1 10-2 1% (five band) 2% (five band) 5% (four band) 10% (four band) * For resistance values less than 10, the third band is either gold or silver. Gold is for a multiplier of 0.1 and silver is for a multiplier of 0.01. 01 What is the resistance and tolerance of each of the four-band resistors? 5.1 k 5% k 5% 47 10% 1.0 5% / 3 2 3 R, K, M.,.
: (potentiometer) (rheostat). (the wiper). Shaft Wiper 3 1 2 Resistive element R Variable resistor (potentiometer) R To connect a potentiometer as a rheostat, one of the outside terminals is connected to the wiper. Variable resistor (rheostat) 1) (voltage l source) 2) (path) 3) (load). An example of a basic circuit is a flashlight, which has each of these plus a control element the switch. Switch Metal strip Circuits are described pictorially with schematics. For example, the flashlight can be represented by Switch Battery Lamp (2 cells) Metal reflector Spring Closed circuit vs. open Circuit
Switches. (pole) (throw) ( ) ( ) SPST SPDT DPST DPDT (a), (b), (c).. l R A = (resistivity) in CM-/ft l = (in feet) A = (in circular mils (CM)) What is the resistance of 400 feet of 22 gage gg copper wire? The area is 642 CM and the resistivity of copper is 10.37 CM-/ft. The table value for resistance/1000 feet of 22 gage wire is 16.14 /1000 feet. By proportion, the resistance of 400 feet is 0.4 x 16.14 = 6.46 By the equation, l 10.37 -CM/ft400 ft R 6.46 A 642 CM
(DMM) DMM,. DMM. OFF V H Hz V H mv H V A 10 A V 40 ma COM VOM (volt-ohm-milliammeter).,,.,. Photo courtesy of Triplett Corporation
Selected Key Terms Selected Key Terms Ampere e Theunit of electrical eec c current. AWG Charge (American Wire Gauge) A standardization based on wire diameter. An electrical property of matter that exists because of an excess or a deficiency i of electrons. Charge can be either or. Circuit An interconnection of electronic components designed to produce a desired result. A basic circuit consists of a source, a load, and an interconnecting path. Conductance The ability of a circuit to allow current. The unit is the siemans (S). Coulomb The unit of electrical l charge. Current Electron The rate of flow of electrical charge. A basic particle of electrical charge in matter. The electron possesses a negative charge. Ground The common or reference pointin i a circuit. it Ohm () The unit of resistance.
Selected Key Terms Potentiometer tio ete A three-terminal e variable beresistor. esso. Resistance The opposition to current. The unit is the ohm (). Rheostat A two-terminal variable resistor. Siemens The unit of conductance. Volt The unit of voltage or electromotive force. 1. The atomic number is the number of a. protons in the nucleus b. neutrons in the nucleus c. protons plus neutrons in the nucleus d. electrons in the outer shell Voltage The amount of energy per charge available to move electrons from one point to another in an electric circuit. 2. Valence electrons are a. in the outer shell b. involved in chemical reactions c. relatively loosely bound d. all of the above 3. The atomic particle responsible for electrical current in solid metallic conductors is the a. proton b. electron cneutron c. d. all of the above
4. The symbol for charge is a. C b. c. Q d. W 5. The definition for voltage is Q a. V t W b. V t W c. V Q d. V It 6. A battery stores 7. The unit of conductance is the a. electrons a. ohm b. protons b. coulomb c. ions c. siemen d. chemical energy d. ampere
8. A four-color resistor with the color bands gray-red- black-gold ld is a. 73 b. 82 c. 680 d. 820 9. A 330 k 5% resistor has the color bands a. red-red-brown-gold b. orange-orange-yellow-gold c. yellow-yellow-red-gold d. yellow-yellow-green-gold 10. The circular mil is a unit of a. length barea b. c. volume d. resistance Answers: 1. a 6. d 2. d 7. c 3. b 8. b 4. c 9. b 5. c 10. b