1. 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.
2. 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
3. Symbol: I
Current Intensity Units: Amperes, A
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
A measure current intensity
4. Potential Difference Symbol: V
(Voltage) Units: Volts, V
Potential Difference causes electrons
to flow through a wire
Provided by a battery or power supply
Example: 12 volts = 12V
V
A voltmeter is used to measure potential
difference
5. Solving for Conductance
(using current intensity & potential difference)
Recall conductance is how easily
current flows through a wire.
To solve use:
G= I
V
Remember:
Units
= Siemens
Symbol = G
6. What is the conductance of a circuit
with a current intensity of 20A & a
potential difference of 5V?
G = I
V
G = 20
5
G = 4S
7. What is the conductance of a circuit
with a current intensity of 5A & a
potential difference of 10V?
G = I
V
G = 5
10
G = 0.5 S
8. What is the conductance of a circuit
with a current intensity of 5A & a
potential difference of 10V?
G = I
V
G = 5
10
G = 0.5 S
9. Sometimes the questions are tricky
and ask you to solve for
conductance from a graph
14
12
current (amps)
10
8
G = ∆I (I2– I1)
6 ∆V (V2-V1)
4
2
0
0 1 2 3 4 5 6 7
voltage (v)
10. Find the conductance using the following graph:
14
12
TWO POINTS
current (amps)
10
8 (2, 4) and (5, 10)
6
4
2 V 1 I1 V 2 I2
0
0 1 2 3 4 5 6 7
voltage (v)
G = ∆I (I2– I1) G = (10 – 4) G= 6 =2S
∆V (V2-V1) (5-2) 3
11. Find the conductance using
the following graph:
24
22
20
18 TWO POINTS
Current (amps)
16
14 (4, 14) and (0, 0)
12
10
8
6
4
2 V 1 I1 V 2 I2
0
0 1 2 3 4 5 6 7
Voltage (v)
G = ∆I (I2– I1) G = (0 - 14) G = -14 = 3.5 S
∆V (V2-V1) (0 - 4) -4
12. Symbol: R
Resistance Units: Ohms, Ω
Resistance is how difficult it is for
current to flow
Resistance is the opposite of conductance!
A resistor is used to slow current down
Resistor– Conductor –
high resistance & low resistance &
low conductance high conductance
13. What is the resistance of a circuit
with a current intensity of 5A & a
potential difference of 10V?
R = V
I
R = 10
5
R= 2Ω
14. What is the current intensity of a
circuit with a resistance of 15Ω & a
potential difference of 10V?
R = V
I
15 = 10
I
15xI = 10
15 15
I = 0.67 A
15. What is the potential difference of a
circuit with a current intensity of 5A &
a resistance of 10 Ω?
R = V
I
10 = V
5
V = 5x10
V = 50 V
16. Summary Table
Resistance Current Potential Conductance
Difference
Slows current The flow of Push of How easily
Definition down electrons electrons or electrons flow
Energy per
charges
Symbol R I V G
Units Ohms (Ω) Amps (A) Volts (V) Siemens (S)
Formula R =V I =V or I = q V = IR or G=I
(if applicable) I R t V=E V
q
How measured
(if applicable) Formula Ammeter Voltmeter Formula and/or
and/or graph graph
17. 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
18. 2nd
3rd
1st 4th
Resistor
Example
Black 0 x1
The resistor on the right Brown 1 x10
has the following value. Red 2 x100
Orange 3 x1000
Yellow 4 x10000
23 x 104 + 10% Ω 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%
19. 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
Relationship between conductance
and resistance
