What is DC Electricity. Chapter 2

Resistance The property of a material to inhibit the flow of current.

Resistor

Resistor Molded Carbon Composite

Resistor Wirewound Film Molded Carbon Composite

Wire wound

Film Surface Mount Technology SMT

Resistivity A L

Resistivity: Example A 1m long piece of gold has a cross sectional area of 0.1cm 2. The resistivity of gold at 20°C is 2.24 X ohm-meters.ρ ρ =2.24 X ohm-meters A = 0.1cm 2 L = 1m

Resistivity: Gold ρ =2.24 X ohm-meters A = 0.1cm 2 L = 1m R = ρL A R = (2.24 X Ώ-m)(1m) m 2 R = Ώ

Resistivity: Carbon ρ =50 X ohm-meters A = 0.1cm 2 L = 1m R = ρL A R = (50 X Ώ-m)(1m) m 2 R =50 Ώ

Resistor Color Code

Tolerance 5% The measure of how good a component is. How close it is to the actual value. 10% 20% GoldSilverNo Band

Tolerance 100Ω 5%: Ω 10%: Ω 20%: Ω

} Digits 36 Multiplier Tolerance 5 % R = Ώ or 3.6M Ώ

} Digits 47 Multiplier Tolerance 20 % R =36 Ώ

Voltage Sources Voltage sources added in Series increase the Voltage and the Current stays the same. V = 1.5v I = 1A V = 4.5v I = 1A

Voltage Sources Voltage sources added in Parallel increase the Current and the Voltage stays the same. V = 1.5v I = 1A V = 1.5v I = 3A

Exampl e Exampl e Battery: V = 1.5v, I = 1A V=3v I= 3A V=3v I=1A

Ohm’s Law The Current(I) in a circuit is directly proportional to the Voltage(E,V) and inversely proportional to the Resistance(R). I = ERER

Ohm’s Law RI E Find: E E = I x R

Ohm’s Law RI E Find: R R = E/I

Ohm’s Law RI E Find: I I = E/R

Ohm’s Law Units RΩRΩ IAIA EvEv

RkΩRkΩ ImAImA E (v)

Ohm’s Law Units RMΩRMΩ IμAIμA E (v)

Ohm’s Law Example RΩRΩ IAIA EvEv R=2Ω, E=12v Find: I I = E/R =12v/2Ω I = 6A

Ohm’s Law Example RkΩRkΩ I mA EvEv E=120, I=60mA Find: R R = E/I =120v/60mA R = 2kΩ

Ohm’s Law Example RkΩRkΩ I mA EvEv R=10kΩ, I=12mA Find: E E = I x R =12mA x 10kΩ I = 120v

Wheel of Answers RΩRΩ IAIA EvEv R kΩ I mA EvEv