Ammeter Voltmeter

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

2. Adding an Ammeter into a
Circuit
 An ammeter measures
the current traveling
through a circuit
 It is always connected
inside the circuit in
series.
A

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

4. 5 Ω
3 Ω
10 Ω
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
A1
A4
A2
A3A1 = 3 amps
A2 = 3 amps
A3 = 3 amps
A4 = 3 amps
IT =3 amps

5. The Everything Table
SERIES PARALLEL
Current (I) SAME DIFFERENT
Potential
Difference (V)
DIFFERENT SAME
Resistance (R) Req = R1 + R2 + R3

6. 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

7. 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

8. 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

9. 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

10. 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

11. Adding a Voltmeter to a Circuit
 A voltmeter measures
the potential difference
traveling through a circuit.
 It is always connected
outside the circuit in
parallel, Katelyn.
V

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

13. 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 V
V3
V4
V =6 V
V =2 V
V2
V =3 V

14. 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 V
V2 = 15
V3 =10 V
V
V1 =?
The reading on the
voltmeter is 5 V

15. 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 V
The reading on the
voltmeter is 18 V

16. 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 = 8V
V
V
V

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

20. 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

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