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Ammeter and VoltmeterObjectives:3.10 Explain the effect of incorporating ameasuring instrument into an electric circuit.
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What is the resistance of a circuitwith a current intensity of 5A & apotential difference of 10V?R = V IR = 10 5R= 2Ω
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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.
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Connecting An AmmeterIn each diagram, is the ammeter hooked up correctlyto these circuits? A AA A A A
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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 A3A1 = 3 amps SERIES PARALLELA2 = 3 amps Current (I) SAME DIFFERENTA3 = 3 amps Potential Difference (V) DIFFERENT SAME Resistance (R) Req = R1 + R2 + R3A4 = 3 amps +… 1 = 1 + 1 + 1 Req R 1 R 2 R 3
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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 PARALLELAmmeters 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
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What is the reading on the ammeters? A1 A3 I1 = 4AIT = 12A I2 = 8 A A2 A4A1 = 12A A2 = 4A A3 = 8A A4 = 12A
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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
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What is the reading on the ammeter (A 1)? A1 I1 = 9A IT = 14A I2 = 5 ARecall IT = I1 + I2So 14A = 9A + I2 A1 must read 5 amps I2 = 5A
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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 A2Recall IT = I1 + I2So IT = 10A + 4A A1 must read 14 amps IT = 14A
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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
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Connecting A VoltmeterIn each diagram, is the voltmeter hooked up correctlyto these circuits? V V V V V V
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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
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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
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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 VThe er VT = ? volt met V2 = 5 V V3 =3 V Note…. VT = V1 + V2 +V3 VT = 10 + 5 + 3 V1 = 18 V
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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 PARALLELVoltmeters 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
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What is the reading on the voltmeters? V1 VT = 12VV1 = 12V V2V2 = 12VV3 = 12V V3
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Problem Solving Using Ammetersand 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….
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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 A1. What is the voltage going through V2 if the reading on theammeter is 2 amps?2. What is the voltage going through VT if the reading on theammeter is 2 amps?
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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 11 I = + Re q 20 5R2 V2 = 1 0.251 I2 R1 = 5Ω = V1 = 20V Re q 1R2 20 = Req = 4Ω1 1 R2 = ?20Ω V2 = 20V A I2 = 1A
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KEY POINTS Voltmeter – always placed outside of circuit attached in parallel Ammeter – is always placed inside circuit attached in series
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