Conductance & Resistance Objectives: 3.3 Measure current intensity in simple circuits. 3.4 Measure potential differences in simple circuits. 3.5 Determine the conductance of a circuit element, using a graph. 3.6 Distinguish between the conductance and the resistance of a circuit.
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Conductance & ResistanceObjectives:3.3 Measure current intensity in simple circuits.3.4 Measure potential differences in simple circuits.3.5 Determine the conductance of a circuit element, using a graph.3.6 Distinguish between the conductance and the resistance of a circuit.
Important Background Information
By now you should have a strong understanding of conductance.
However, before we move on to circuits we must first understand the terms CURRENT INTENSITY and POTENTIAL DIFFERENCE
Symbol: IUnits: Amperes, ACurrent Intensity
Current: the amount of electrons that flow through a wire
Example: 0.7 amperes is shown by I = 0.7 A
An ammeter is the instrument used to measure current intensityA
Symbol: VUnits: Volts, V
Potential Difference(Voltage)
Potential Difference causes electrons to flow through a wire
Provided by a battery or power supply
Example: 12 volts = 12V
A voltmeter is used to measure potential difference
V
Solving for Conductance(using current intensity & potential difference)
Recall conductance is how easily current flows through a wire.
To solve use:
Remember: Units = Siemens Symbol = G
G = I V
What is the conductance of a circuit with a current intensity of 20A & a potential difference of 5V?G = I
VG = 20
5
G = 4 S
What is the conductance of a circuit with a current intensity of 5A & a potential difference of 10V?G = I
VG = 5
10
G = 0.5 S
What is the conductance of a circuit with a current intensity of 5A & a potential difference of 10V?G = I
VG = 5
10
G = 0.5 S
Sometimes the questions are tricky and ask you to solve for
conductance from a graph
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7
voltage (v)
curr
ent
(am
ps)
G = ∆I (I2– I1) ∆V (V2-V1)
Find the conductance using the following graph:
0
2
4
6
8
10
12
14
0 1 2 3 4 5 6 7
voltage (v)
curr
ent (
amps
) TWO POINTS
(2, 4) and (5, 10)
V1 I1 V2 I2
G = ∆I (I2– I1) ∆V (V2-V1)
G = (10 – 4) (5-2)
G = 6 = 2 S 3
Find the conductance using
the following graph:
TWO POINTS
(4, 14) and (0, 0)
V1 I1 V2 I2
G = ∆I (I2– I1) ∆V (V2-V1)
G = (0 - 14) (0 - 4)
G = -14 = 3.5 S -4
02468
1012141618202224
0 1 2 3 4 5 6 7
Voltage (v)
Cu
rren
t (a
mp
s)
Symbol: RUnits: Ohms, Ω Resistance
Resistance is how difficult it is for current to flow
Resistance is the opposite of conductance!
A resistor is used to slow current down
Conductor – low resistance & high conductance
Resistor– high resistance & low conductance
What is the resistance of a circuit with a current intensity of 5A & a potential difference of 10V?R = V
IR = 10
5R = 2 Ω
What is the current intensity of a circuit with a resistance of 15Ω & a potential difference of 10V?R = V
I15 = 10
I15xI = 10 15 15 I = 0.67 A
What is the potential difference of a circuit with a current intensity of 5A & a resistance of 10 Ω?R = V
I10 = V
5V = 5x10
V = 50 V
Summary Table
Resistance Current Potential Difference
Conductance
DefinitionSlows current
downThe flow of electrons
Push of electrons or Energy per
charges
How easily electrons flow
Symbol R I V G
Units Ohms (Ω) Amps (A) Volts (V) Siemens (S)
Formula(if applicable)
R =V I
I =V or I = q R t
V = IR orV = E q
G = I V
How measured(if applicable) Formula
and/or graphAmmeter Voltmeter Formula and/or
graph
Conductance and Resistance of a Circuit Element
Resistors are coated with ceramic.
They have color coated bands to indicate resistance
1st & 2nd band first two digits of resistance
3rd band exponential of 10 by which the first two digits must be multiplied (multiplier)
4th band tolerance
Resistor
Example
Black 0 x1
Brown 1 x10
Red 2 x100
Orange 3 x1000
Yellow 4 x10000
Green 5 x100000
Blue 6 x1000000
Violet 7 x10000000
Gray 8 x100000000
White 9
The last band indicates the tolerance
Gold +5% Gray +10% None +20%
The resistor on the right has the following value.
23 x 104 + 10%
1st
2nd
3rd4th
Key Points
See Summary Table Finding conductance with formula
and graph (refer to examples. Very important & on exam!)
Definitions of current, potential difference, conductance and resistance