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

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

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 SERIESPARALLEL Current (I)SAMEDIFFERENT Potential Difference (V) DIFFERENTSAME Resistance (R) Req = R 1 + R 2 + R 3 + … A1A1 A4A4 A2A2 A3A3 A 1 = 3 amps A 2 = 3 amps A 3 = 3 amps A 4 = 3 amps I T =3 amps

Adding an Ammeter into a Parallel Circuit Ammeters placed in a parallel circuit can have different readings. SERIESPARALLEL Current (I)SAMEDIFFERENT Potential Difference (V) DIFFERENTSAME Resistance (R) Req = R 1 + R 2 + R 3 + … Recall in parallel, current is different. I T = 8 A AI 1 = 6A I 2 = 2 A AA A I T = 8 A

I T = 12A A4A4 I 1 = 4A I 2 = 8 A A1A1 A3A3 A2A2 What is the reading on the ammeters? A 1 = 12AA 2 = 4AA 3 = 8AA 4 = 12A

R eq A4A4 R1R1 R2R2 A1A1 A3A3 A2A2 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 Which ammeter correctly measures the total current? Ammeter #1 & 4 measures the total current

I T = 14A I 1 = 9A I 2 = 5 A A1A1 What is the reading on the ammeter (A 1 )? RecallI T = I 1 + I 2 So 14A = 9A + I 2 I 2 = 5A A 1 must read 5 amps

A3A3 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 )? RecallI T = I 1 + I 2 So I T = 10A + 4A I T = 14A A 1 must read 14 amps A1A1 A2A2 I 1 = 10 A I 2 = 4 A I T = 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 V V V V V V

In a series circuit a voltmeter does NOT read the same throughout the entire circuit. Voltmeter In A Series Circuit SERIESPARALLEL Current (I)SAMEDIFFERENT Potential Difference (V) DIFFERENTSAME Resistance (R) Req = R 1 + R 2 + R 3 + … V1V1 Notice…. Voltmeter 1 = Voltmeter 2 + Voltmeter 3 + Voltmeter 4 V T =11 V V3V3 V4V4 V =6 V V =2 V V2V2 V =3 V

For this series circuit, what is the reading on the voltmeter given the following information? Note…. V T = V 1 + V 2 +V 3 30 = V V 1 = 5 V V T =30 V V 2 = 15 V 3 =10 V V V 1 =? The reading on the voltmeter is 5 V

For this series circuit, what is the reading on the voltmeter given the following information? Note…. V T = V 1 + V 2 +V 3 V T = V 1 = 18 V V T = ? V 2 = 5 V V 3 =3 V V V 1 =10 V The 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. SERIESPARALLEL Current (I)SAMEDIFFERENT Potential Difference (V) DIFFERENTSAME Resistance (R) Req = R 1 + R 2 + R 3 + … Recall in parallel, potential difference is the same. V T = 8V V 1 = 8V V 2 = 8V V V V

V T = 12V V1V1 V2V2 What is the reading on the voltmeters? V 1 = 12V V 2 = 12V V 3 = 12V V3V3

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….

I T = I 2 = I 3 = I 1 = V T = V 2 = V 1 = V 3 = R 1 = 12 Ω R 2 = 6 Ω R 3 = 2 Ω R eq = 20 Ω 2 A 12 V SERIESPARALLEL Current (I)SAMEDIFFERENT Potential Difference (V) DIFFERENTSAME Resistance (R) Req = R 1 + R 2 + R 3 + … 1. What is the voltage going through V 2 if the reading on the ammeter is 2 amps? A 2 A 2. What is the voltage going through V T if the reading on the ammeter is 2 amps?

If the voltmeter reads 20V & the ammeter reads 1A, solve for the equivalent resistance, R eq ? V R 1 = 5Ω A V T = 20V I 2 = 1A V 1 = 20V V 2 = 20V R 2 = ? 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  Google Images  Animation Factory

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