Module 2 ammeter and voltmeter
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Ammeter and VoltmeterObjectives:3.10 Explain the effect of incorporating a measuring instrument into an electric circuit.
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
Adding an Ammeter into a Circuit
In order to measure the current traveling through a circuit, an ammeter must be inserted into the circuit.
An ammeter is always connected inside the circuit in series.
A
In each diagram, is the ammeter hooked up correctly to these circuits?
Connecting An Ammeter
A
A
A
A
A A
5
3 10
In a series circuit an ammeter can be placed anywhere along the wire and it will have the same current intensity reading.
Adding An Ammeter In A Series Circuit
SERIES PARALLEL
Current (I) SAME DIFFERENT
Potential Difference (V)
DIFFERENT SAME
Resistance (R) Req = R1 + R2 + R3 + …
1 2 3
1 1 1 1= + +
Req R R R
A1
A4
A2
A3
A1 = 3 amps
A2 = 3 amps
A3 = 3 amps
A4 = 3 amps
IT =3 amps
Adding an Ammeter into a Parallel Circuit
Ammeters placed in a parallel circuit can have different
readings.
SERIES PARALLEL
Current (I) SAME DIFFERENT
Potential Difference (V)
DIFFERENT SAME
Resistance (R)
Req = R1 + R2 + R3 + …
1 2 3
1 1 1 1= + +
Req R R R
Recall in parallel, current is different.
IT = 8 A
AI1 = 6A
I2 = 2 AA A
A
IT = 8 A
IT = 12A
A4
I1 = 4A
I2 = 8 A
A1 A3
A2
What is the reading on the ammeters?
A1 = 12A A2 = 4A A3 = 8A A4 = 12A
Req
A4
R1
R2
A1
A3
A2
Which ammeter correctly measures the current flowing through R1?
Ammeter #2 measures the current flowing through R1
Which ammeter correctly measures the current flowing through R2?
Ammeter #3 measures the current flowing through R2
Which ammeter correctly measures the total current?
Ammeter #1 & 4 measures the total current
IT = 14A
I1 = 9A
I2 = 5 A
A1
What is the reading on the ammeter (A1)?
Recall IT = I1 + I2
So 14A = 9A + I2
I2 = 5A
A1 must read 5 amps
A3
If the reading on ammeter 2 (A2) is 10 amps & the reading on ammeter 3 (A3) is 4 amps, what is the
reading on ammeter 1 (A1)?
Recall IT = I1 + I2
So IT = 10A + 4A
IT = 14A
A1 must read 14 amps
A1
A2
I1 = 10 A
I2 = 4 AIT = 14 A
Adding a Voltmeter to a Circuit
In order to measure the voltage or potential difference traveling through a circuit, a voltmeter must be inserted into the circuit.
A voltmeter is always connected outside the circuit in parallel.
V
In each diagram, is the voltmeter hooked up correctly to these circuits?
Connecting A Voltmeter
VV
V
V
V
V
In a series circuit a voltmeter does NOT read the same throughout the entire circuit.
Voltmeter In A Series Circuit
SERIES PARALLEL
Current (I) SAME DIFFERENT
Potential Difference (V)
DIFFERENT SAME
Resistance (R) Req = R1 + R2 + R3 + …
1 2 3
1 1 1 1= + +
Req R R R
V1
Notice….Voltmeter 1 = Voltmeter 2 + Voltmeter 3
+ Voltmeter 4
VT =11 VV3
V4
V =6 V
V =2 V
V2V =3 V
For this series circuit, what is the reading on the voltmeter given the following information?
Note…. VT = V1 + V2 +V3
30 = V1 + 15 + 10
V1 = 5 V
VT =30 VV2 = 15
V3 =10 V
V
V1 =?The reading on the
voltmeter is 5 V
For this series circuit, what is the reading on the voltmeter given the following information?
Note…. VT = V1 + V2 +V3
VT = 10 + 5 + 3
V1 = 18 V
VT = ?V2 = 5 V
V3 =3 V
V
V1 =10 VThe reading on the
voltmeter is 18 V
Adding a Voltmeter into a Parallel Circuit
Voltmeters placed in a parallel circuit will have the same
readings.
SERIES PARALLEL
Current (I) SAME DIFFERENT
Potential Difference (V)
DIFFERENT SAME
Resistance (R)
Req = R1 + R2 + R3 + …
1 2 3
1 1 1 1= + +
Req R R R
Recall in parallel, potential difference is the same.
VT = 8V
V1 = 8V
V2 = 8VV
V
V
VT = 12V
V1
V2
What is the reading on the voltmeters?
V1 = 12V
V2 = 12V
V3 = 12V V3
Problem Solving Using Ammeters and Voltmeters
It is important to be able to use all of
the information discussed in this section and apply it to
solving circuits.
Let’s try some problems….
IT =
I2 =
I3 =
I1 =VT =
V2 =
V1 =
V3 =
R1 = 12 Ω
R2 = 6 Ω
R3 = 2 Ω
Req = 20 Ω
2 A
2 A
2 A12 V
SERIES PARALLEL
Current (I) SAME DIFFERENT
Potential Difference (V)
DIFFERENT SAME
Resistance (R) Req = R1 + R2 + R3 + …
1 2 3
1 1 1 1= + +
Req R R R
1. What is the voltage going through V2 if the reading on the ammeter is 2 amps?
A
2 A
2. What is the voltage going through VT if the reading on the ammeter is 2 amps?
R V
1 I
6 V
1 2
V=12V
R V
1 I
20 V
1 2
V=40V
If the voltmeter reads 20V & the ammeter reads 1A, solve for the equivalent resistance, Req?
V
R1 = 5Ω
A
VT = 20V
I2 = 1A
V1 = 20V
V2 = 20V
I
V
1
R
2
22
I
V
1
R
1
20
1
R2
R2 = ?
21
11
Re
1
RRq
5
1
20
1
Re
1
q
1
25.0
Re
1
q
Req = 4Ω
20Ω
KEY POINTS
Voltmeter – always placed outside of circuit attached in parallel
Ammeter – is always placed inside circuit attached in series
Activities
Worksheet # 14
References
Student Study Guide – Physical Science 416/436 - MEQ
Science Quest – Grenier, Daigle, Rheaume – 1998, Cheneliere
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