The reading of the ammeter and the reading of the voltmeter.

In summary, the conversation discusses a circuit with two keys and determining the readings of the ammeter and voltmeter in three different cases. The equations and attempts at solutions are provided, and the expert confirms that all three cases are correct. The physics explanation for the voltage being zero in case two is also discussed, with the key S2 short-circuiting the 5 ohm resistor. The expert also provides their opinion on the solution.
  • #1
Asmaa Mohammad
182
7

Homework Statement


In this circuit
bYQ3m.jpg

What will be the reading of the ammeter and that of the voltmeter when:
1. Key S1 and key S2 are open.
2. Key S1 and key S2 are closed.
3. Key S1 is closed and key S2 is open.
(Neglect the internal resistance of the source)

Homework Equations

The Attempt at a Solution


That might be an easy question, but my book doesn't give the solution, and I want to amke sure of my work.

Case 1.
i = 0
V = 2V

Case 2.
i = V/R =2/3 A
V = Vb - iR = 2 - ((2/3) * 3 = 0

Case 3.
Rt = 5+3 = 8 ohm
i = V/Rt = 2/8 = 0.25 A

V = iR = 0.25 * 5 = 1.25 V

So, is my answer correct.
 
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  • #2
Yes, I think you have got all 3 right.
 
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  • #3
Ok, but I can't understand why in case two the voltage will be zero? I understand the maths but I don't understand the physics explanation.
 
  • #4
Asmaa Mohammad said:
Ok, but I can't understand why in case two the voltage will be zero? I understand the maths but I don't understand the physics explanation.
What does S2 do to the 5 ohm resistor?
 
  • #5
cnh1995 said:
What does S2 do to the 5 ohm resistor?
S2 cancels the resistance 5 ohm.
But we do still have the resistance 3 ohm.
 
  • #6
Asmaa Mohammad said:
S2 cancels the resistance 5 ohm.
In technical terms, S2 short-circuits the 5 ohm resistor. So the 5 ohm resistor is ineffective.
 
  • #7
cnh1995 said:
In technical terms, S2 short-circuits the 5 ohm resistor. So the 5 ohm resistor is ineffective.
OK, and then what? more explanation please!
 
  • #8
Asmaa Mohammad said:
OK, and then what? more explanation please!
What is the resistance of S2 and the wire that shorts the 5 ohm resistance?
 
  • #9
It is zero so the voltage is zero.
Ok, I got it. But what's your opinion about the whole solution?
 
  • #10
Asmaa Mohammad said:
It is zero so the voltage is zero.
Ok, I got. But what's your opinion about the whole solution?
andrevdh said:
I think you have got all 3 right.
 
  • #11
the current calculation (correctly) assumes the resistance of the parallel combination is zero and for the voltage it subtracts the voltage drop over the 3 ohm resistor from the power supply's voltage to obtain the voltage over the combination (the remaining part of the circuit) - a bit of a merry go round way of doing the calculation if you ask me. Words would have done better to provide the answer.
 
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FAQ: The reading of the ammeter and the reading of the voltmeter.

1. How do you read an ammeter?

An ammeter is a device used to measure the flow of electrical current in a circuit. To read an ammeter, you must first connect it in series with the circuit. Then, simply read the numerical value displayed on the ammeter in units of amperes (A).

2. What does a voltmeter measure?

A voltmeter is a device used to measure the potential difference or voltage in an electrical circuit. It is connected in parallel with the circuit and the numerical value displayed on the voltmeter represents the voltage in units of volts (V).

3. How do you connect an ammeter and a voltmeter in a circuit?

An ammeter must be connected in series with the circuit, meaning it is placed in the path of the current flow. On the other hand, a voltmeter must be connected in parallel with the circuit, meaning it is connected across the component being measured.

4. What is the difference between an ammeter and a voltmeter?

An ammeter measures the flow of current in a circuit, while a voltmeter measures the potential difference or voltage. Ammeters are connected in series with the circuit, while voltmeters are connected in parallel.

5. Why are ammeters and voltmeters important in electrical circuits?

Ammeters and voltmeters are important tools for measuring and monitoring the electrical properties of a circuit. They allow scientists to accurately measure the flow of current and voltage, which is crucial for understanding and troubleshooting any issues in the circuit.

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