Ammeter and Voltmeter Objectives 3 10 Explain the

Ammeter and Voltmeter Objectives: 3. 10 Explain the effect of incorporating a measuring instrument into an electric circuit.

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

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

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. A 1 IT =3 amps A 4 A 2 5 W 3 W 10 W A 3 A 1 = 3 amps A 2 = 3 amps A 3 = 3 amps A 4 = 3 amps SERIES PARALLEL SAME DIFFERENT Potential Difference (V) DIFFERENT SAME Resistance (R) Req = R 1 + R 2 + R 3 +… Current (I)

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

What is the reading on the ammeters? A 1 A 3 I 1 = 4 A IT = 12 A I 2 = 8 A A 2 A 4 A 1 = 12 A A 2 = 4 A A 3 = 8 A A 4 = 12 A

Which ammeter correctly measures the current flowing through R 1? Ammeter #2 measures the current flowing through R 1 Which ammeter correctly measures the current flowing through R 2? Ammeter #3 measures the current flowing through R 2 A 1 A 3 R 1 Req A 2 R 2 A 4 Which ammeter correctly measures the total current? Ammeter #1 & 4 measures the total current

What is the reading on the ammeter (A 1)? A 1 I 1 = 9 A IT = 14 A Recall IT = I 1 + I 2 So 14 A = 9 A + I 2 = 5 A I 2 = 5 A A 1 must read 5 amps

If the reading on ammeter 2 (A 2) is 10 amps & the reading on ammeter 3 (A 3) is 4 amps, what is the reading on ammeter 1 (A 1)? A 1 I 1 = 10 A A 3 I 2 = 4 A IT = 14 A A 2 Recall IT = I 1 + I 2 So IT = 10 A + 4 A IT = 14 A A 1 must read 14 amps

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

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

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

For this series circuit, what is the reading on the voltmeter given the following information? V the n o ing 5 V d a e r The meter is volt V 1 =? VT =30 V V 2 = 15 V 3 =10 V Note…. V T = V 1 + V 2 +V 3 30 = V 1 + 15 + 10 V 1 = 5 V

For this series circuit, what is the reading on the voltmeter given the following information? V the n o ing d a 8 V e 1 r s e i Th ter e m t vol VT = ? V 3 =3 V V 1 =10 V V 2 = 5 V Note…. V T = V 1 + V 2 +V 3 VT = 10 + 5 + 3 V 1 = 18 V

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

What is the reading on the voltmeters? V 1 VT = 12 V V 1 = 12 V V 2 = 12 V V 3

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….

SERIES PARALLEL SAME DIFFERENT Potential Difference (V) DIFFERENT SAME Resistance (R) Req = R 1 + R 2 + R 3 +… Current (I) Req = 20 Ω VT = IT = 2 A A R 1 = 12 Ω V 1 = I 1 = 2 A R 2 = 6 Ω R 3 = 2 Ω V 3 = V 2 = 12 V I 2 = 2 A I 3 = 2 A 1. What is the voltage going through V 2 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?

If the voltmeter reads 20 V & the ammeter reads 1 A, solve for the equivalent resistance, Req? V VT = 20 V R 1 = 5Ω V 1 = 20 V Req = 4Ω R 2 = ? 20Ω V 2 = 20 V I 2 = 1 A A

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 ¡ Google Images ¡ Animation Factory ¡

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