1. Ammeter and Voltmeter
Objectives:
3.10 Explain the effect of incorporating a
measuring instrument into an electric circuit.

2. 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

3. 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 A
connected inside the
circuit in series.

4. Connecting An Ammeter
In each diagram, is the ammeter hooked up correctly
to these circuits?
A
A
A
A
A A

5. Adding An Ammeter In A Series Circuit
In a series circuit an ammeter can be placed
anywhere along the wire and it will have the same
current intensity reading.
A1 A2
IT =3 amps 5Ω
3Ω
A4 10 Ω
A3
A1 = 3 amps
SERIES PARALLEL
A2 = 3 amps Current (I) SAME DIFFERENT
A3 = 3 amps Potential Difference
(V)
DIFFERENT SAME
Resistance (R) Req = R1 + R2 + R3
A4 = 3 amps +…
1
=
1
+
1
+
1
Req R 1 R 2 R 3

6. Adding an Ammeter into a Parallel
Circuit
IT = 8 A
A
IT = 8 A A A I2 = 2 A
I1 = 6A A
Recall in parallel, current is different.
SERIES PARALLEL
Ammeters placed in a parallel Current (I) SAME DIFFERENT
circuit can have different Potential DIFFERENT SAME
readings. Difference (V)
Resistance Req = R1 + R2 1 1 1 1
+ R3 + … = + +
(R) Req R 1 R 2 R 3

7. What is the reading on the ammeters?
A1
A3
I1 = 4A
IT = 12A
I2 = 8 A
A2
A4
A1 = 12A A2 = 4A A3 = 8A A4 = 12A

8. 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
A1
R1 A3
Req
A2 R2
A4
Which ammeter correctly measures the total
current?
Ammeter #1 & 4 measures the total current

9. What is the reading on the ammeter (A 1)?
A1
I1 = 9A
IT = 14A
I2 = 5 A
Recall IT = I1 + I2
So 14A = 9A + I2 A1 must read 5 amps
I2 = 5A

10. 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)?
A1 I1 = 10 A A3
IT = 14 A I2 = 4 A
A2
Recall IT = I1 + I2
So IT = 10A + 4A A1 must read 14 amps
IT = 14A

11. 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

12. Connecting A Voltmeter
In each diagram, is the voltmeter hooked up correctly
to these circuits?
V
V
V
V
V
V

13. Voltmeter In A Series Circuit
In a series circuit a voltmeter does NOT read the
same throughout the entire circuit.
V2 V =3 V
V1
VT =11 V
V3 V =6 V
V4
SERIES PARALLEL
V =2 V Current (I) SAME DIFFERENT
Notice…. Potential Difference DIFFERENT SAME
(V)
Voltmeter 1 = Voltmeter 2 + Voltmeter 3 Req = R1 + R2 + R3
Resistance (R) 1
=
1
+
1
+
1
+ Voltmeter 4 +…
Req R 1 R 2 R 3

14. For this series circuit, what is the reading on the
voltmeter given the following information?
V
he
ng on t
er eadi is 5
V V1 =?
Th ter VT =30 V
voltme
V2 = 15
V3 =10 V
Note….
VT = V1 + V2 +V3
30 = V1 + 15 + 10
V1 = 5 V

15. For this series circuit, what is the reading on the
voltmeter given the following information?
V
he
ng on t
r eadi is 18 V V1 =10 V
The er VT = ?
volt met
V2 = 5 V
V3 =3 V
Note….
VT = V1 + V2 +V3
VT = 10 + 5 + 3
V1 = 18 V

16. Adding a Voltmeter into a Parallel
Circuit
V1 = 8V
VT = 8V V
V2 = 8V
V
V
Recall in parallel, potential difference is the same.
SERIES PARALLEL
Voltmeters placed in a parallel Current (I) SAME DIFFERENT
circuit will have the same Potential DIFFERENT SAME
readings. Difference (V)
Req = R1 + R2
Resistance 1 1 1 1
+ R3 + … = + +
(R) Req R 1 R 2 R 3

17. What is the reading on the voltmeters?
V1
VT = 12V
V1 = 12V V2
V2 = 12V
V3 = 12V V3

18. 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….

19. SERIES PARALLEL
Current (I) SAME DIFFERENT
Potential Difference DIFFERENT SAME
(V)
Resistance (R) Req = R1 + R2 + R3 1 1 1 1
= + +
+… Req R 1 R 2 R 3
R V Req = 20 Ω R1 = 12 Ω
=
1 I R V
VT = V1 = =
1 I
20 V IT = 2 A I1 = 2 A
=
1 2 6 V
A =
R2 = 6 Ω 1 2
V=40V V2 = 12 V
R3 = 2 Ω V=12V
I2 = 2 A
V3 =
I3 = 2 A
1. What is the voltage going through V2 if the reading on the
ammeter is 2 amps?
2. What is the voltage going through VT if the reading on the
ammeter is 2 amps?

20. If the voltmeter reads 20V & the ammeter reads 1A,
solve for the equivalent resistance, Req?
VT = 20V
1 1 1
V = +
R V Re q R1 R2
= 1 1 1
1 I = +
Re q 20 5
R2 V2
= 1 0.25
1 I2 R1 = 5Ω =
V1 = 20V Re q 1
R2 20
= Req = 4Ω
1 1
R2 = ?20Ω
V2 = 20V A
I2 = 1A

21. KEY POINTS
 Voltmeter – always placed outside of
circuit attached in parallel
 Ammeter – is always placed inside
circuit attached in series

22. Activities
 Worksheet # 14

23. References
 Student Study Guide – Physical
Science 416/436 - MEQ
 Science Quest – Grenier, Daigle,
Rheaume – 1998, Cheneliere
 Google Images
 Animation Factory

24. Alternative Educational Experiences
through e-Learning