Resistance in Circuits What is it l Resistance

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Resistance in Circuits

Resistance in Circuits

What is it? l Resistance is the ability to impede (oppose) the flow of

What is it? l Resistance is the ability to impede (oppose) the flow of electrons

What is the effect of resistance? l l When electrons flow through a load,

What is the effect of resistance? l l When electrons flow through a load, or a conductor, resistance causes a loss in voltage There is now a difference in the amount of voltage after the electron has flowed through the load

Short form: R l Unit: ohm (Ω) l Circuit Symbol: l

Short form: R l Unit: ohm (Ω) l Circuit Symbol: l

Resistance l Resistance is measured with an ohmmeter in parallel with the load

Resistance l Resistance is measured with an ohmmeter in parallel with the load

Factors affecting resistance

Factors affecting resistance

Factors affecting resistance l l l Type of material: some materials conduct better than

Factors affecting resistance l l l Type of material: some materials conduct better than others Cross-sectional area: as area increases, resistance decreases Length of wire: as length increases, resistance increases Temperature: as temperature increases, resistance increases Resistor: type of load

Relating Current, Voltage, and Resistance – Ohm’s Law l l As the potential difference

Relating Current, Voltage, and Resistance – Ohm’s Law l l As the potential difference across a load increases, so does the current. As the resistance increases current decreases

Ohm’s Law l. V =Ix. R l. R = V ÷ I l. I

Ohm’s Law l. V =Ix. R l. R = V ÷ I l. I = V ÷ R V I R

An Example: A load has 1. 2 A of current flowing through it. The

An Example: A load has 1. 2 A of current flowing through it. The voltage across the load is 6. 0 V. Calculate the resistance of the load. Given: I = 1. 2 A V = 6. 0 V Required: R = ? Analysis: R = V ÷ I Solution: R = 6. 0 ÷ 1. 2 l =5Ω Statement: The resistance of the load will be 5 Ω.

Ohm-my goodness – homework! Electric Current Read 556 - 557 Potential Difference Read 560

Ohm-my goodness – homework! Electric Current Read 556 - 557 Potential Difference Read 560 -561 Resistance in Circuits Read 564 -565 Questions: pg. 570 # 4 - 8

Resistance 4. (pg. 570) Resistance Voltage Current 480 270 110 1 000 001 370

Resistance 4. (pg. 570) Resistance Voltage Current 480 270 110 1 000 001 370 120 337. 5 25 120 2 220 0. 25 1. 25 0. 23 0. 000 12 6. 0

Resistance 5. Given: I = 2. 0 A V = 36 V Required: R

Resistance 5. Given: I = 2. 0 A V = 36 V Required: R = ? Analysis: R = V ÷ I Solution: R = 36 ÷ 2. 0 = 18 Ω Statement: The resistance of the load will be 18 Ω.

Resistance 6. Given: R = 4 Ω V = 19 V Required: I =

Resistance 6. Given: R = 4 Ω V = 19 V Required: I = ? Analysis: I = V ÷ R Solution: I = 19 ÷ 4 = 4. 75 A Statement: The current going through the adapter will be 4. 75 A.

Resistance 7. Given: R = 8 Ω I = 15 A Required: V =

Resistance 7. Given: R = 8 Ω I = 15 A Required: V = ? Analysis: V = I X R Solution: V = 15 X 8 = 120 V Statement: The voltage across the energy source will be 120 V.

Resistance 8. Given: I = 505 A V = 12 V Required: R =

Resistance 8. Given: I = 505 A V = 12 V Required: R = ? Analysis: R = V ÷ I Solution: R = 12 ÷ 505 = 0. 024 Ω Statement: The resistance of the starter motor will be 0. 024 Ω.