1. Resistance and Conductance
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Ch. 5, pg

2. What is resistance in an electrical circuit?
In an electrical circuit, each part has a specific job, or function
The function of resistors is to transform electrical energy into another form of energy.
In an electrical circuit, resistors are described as a force that hinders the flow of the circuit.
The higher the resistance of the material, the more energy it takes for the current to flow.

3. Electrical Resistance
Electrical Resistance: the ability of a material to hinder the flow of electrical current
Resistors are also known as insulators.
The opposite of a resistor or insulator is a conductor.
A good conductor is a poor resistor and a poor conductor is a good resistor
Resistors/Insulators
Conductors
Materials which slow down or stop the flow of electrons
Materials which allow the flow of electrons
Examples: plastic, glass, ceramic, tungsten, wood and distilled water
Examples: metals, acids, salt water and bases

4. Factors effecting resistance and conductance
Description
Nature
Poor conductors = good resistors, good resistors = poor conductors
Length
Longer = greater resistance
Diameter
Smaller = greater resistance
Temperature
Warmer = greater resistance
Describe what properties a wire would have to be a good conductor
Describe what properties a plastic would have to be a good resistor

5. Example:
There are six electrical wires made of the same substance and having the same length : three have a diameter of 1.5 mm while the other three have a diameter of 3.0 mm. They are placed either end to end to increase the length of the wire or parallel to one another to increase the surface area of the wire. Which three wire arrangement offers the least resistance to the flow of electric current? A) B) C) D)

6. Measuring Resistance
Resistance is measured in ohms, which is symbolized by the Greek letter omega: Ω
One ohms is equal to:
Ω = V A
V= volts (potential difference)
A = amps (current intensity)

7. Ohms Law
Defn: For a given resistance, the potential difference in an electrical circuit is directly proportional to the current intensity
V = RI
V = potential difference (in volts)
R = resistance (in Ω)
I = the current intensity (in amps)
* Ohms law applies only to conductors (not insulators)

8. Sample Questions
Finding the resistance when the resistance graph is given
1- The following graph illustrates the change in potential difference (voltage), V, as a function of the current intensity, I, in a circuit.
What is the resistance of this circuit?
A) 0.1 Ω B) 3.0 Ω C) 10.0 Ω D) 15.0 Ω

9. 2- The following graph illustrates the change in the current intensity, I, in a circuit element as a function of the potential difference (voltage), V, across its terminals: What is the resistance of this circuit element? A) 0.20 Ω B) 5.0 Ω C) 7.2 Ω D) 28.8 Ω

10. Finding resistance when conductance graph is given
1- The following graph illustrates the change in the current intensity, I, in a circuit as a function of the potential difference (voltage), V, across its terminals
What is the resistance of this circuit?
A) 0.33 Ω B) 0.75 Ω C) 1.33 Ω D) 3.00 Ω

11. 2- The following graph illustrates the change in electric current intensity, I, as a function of potential difference (voltage), V, for a given resistor. According to this graph, what is the resistance of this resistor? A) 0.15 Ω B) 5.4 Ω C) 6.7 Ω D) 21.6 Ω

12. Finding resistance using a provided data table
1- Use the table to make a resistance graph and find the resistance of the resistor
Voltage (V) 1 2 3 4 5
Intensity (A)
0.2
0.4
0.6
0.8
1.0

13. 2- Use the table to make a resistance graph and find the resistance of the resistor
Voltage (V) 2
3.5
4.3
5.1
6.5
Intensity (A)
0.3
0.8
1.4
1.9
2.2