Ammeters and voltmeters in series

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In summary, when an ammeter and a voltmeter are joined in series to a cell, their readings are A and V respectively. If a resistance is then joined in parallel with the voltmeter, the readings will change. According to the conversation, the potential difference across the terminals of the battery will change as soon as current flows through it, meaning that either the battery or the meters (or both) are not ideal. This leads to the conclusion that when a resistance is joined in parallel with the voltmeter, A will increase and V will decrease, as stated in option D.
  • #1
Tanishq Nandan
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Homework Statement



An ammeter and a voltmeter are joined in series to a cell.Their readings are A and V respectively.If a resistance is now joined in parallel with the voltmeter,
A)both A and V will increase
B)both A and V will decrease
C)A will decrease,V will increase
D)A will increase,V will decrease

Homework Equations


[/B]
Basic theory behind ammeters and voltmeters:
▪Ammeter:Used for measuring current.In essence,it is a galvanometer (current detecting device) attached to a very small resistance attached to it in parallel(small so that it doesn't hinder the current it is measuring and gives an accurate reading)

▪Voltmeter:Used for measuring potential difference.In essence,it is a galvanometer with a very high
resistance attached to it in series (High so that it doesn't allow current to flow through it,which would change the amount of current across the element being measured, and correspondingly change the potential difference across it,preventing us from getting an accurate reading)

The Attempt at a Solution


[/B]
An ideal voltmeter has a resistance of infinity,so when it is connected with a cell in series,along with an ammeter,the only path for current to traverse the entire circuit would be through the voltmeter,but the high resistance wouldn't allow it to flow.

So,the initial readings according to me ought to read:
[Assuming emf of cell to be E]
A=0 (no current through the circuit)
V=E (potential across its two ends)

Now,as soon as we connect a resistor through it,it provides the current a path to flow,so now we have a current flowing through the circuit.
So,final readings according to me should be:
[Assuming resistance connected to be R]

A=E/R(which is obviously greater than before)
V=?HERE LIES MY PROBLEM?

Isn't the potential difference across the two ends same as before??
Answers D by the way,so hopefully my method of deducing A was right(If it wasn't,please do inform me)
But,I am stuck on V.
 
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  • #2
Tanishq Nandan said:
Isn't the potential difference across the two ends same as before?
Yes, as long as you assume the source is an ideal one with no internal resistance. Why do you see this as a problem?

Any time you get stuck on this kind of problem you should draw a circuit diagram and label it will all known conditions (and if you have, as you do here, two different set of conditions, draw it twice).
 
  • #3
phinds said:
Why do you see this as a problem?
Coz the answer given is D:A increases,whereas V decreases.There isn't any option for V remains same,which is bugging me.
 
  • #4
So, you need to decide. Am I wrong or is the question using an unstated assumption?
 
  • #5
Tanishq Nandan said:
Coz the answer given is D:A increases,whereas V decreases.There isn't any option for V remains same,which is bugging me.
What is V? And what is E?
 
  • #6
cnh1995 said:
What is V? And what is E?
There's no E...A and V are the readings on the ammeter and voltmeter respectively.
 
  • #7
Tanishq Nandan said:
Assuming emf of cell to be E]
E is the emf of the cell.
Tanishq Nandan said:
There isn't any option for V remains same,which is bugging me.

What will remain unchanged? V or E?
 
  • #8
cnh1995 said:
E is the emf of the cell.What will remain unchanged? V or E?
According to me,V
 
  • #9
Tanishq Nandan said:
According to me,V
Why? And why not E?
 
  • #10
cnh1995 said:
Why? And why not E?
Okk,yeah,I get your point,the potential difference across the terminals of a battery change as soon as current flows through it.(If the battery isn't ideal,of course)
 
  • #11
Tanishq Nandan said:
Okk,yeah,I get your point,the potential difference across the terminals of a battery change as soon as current flows through it.(If the battery isn't ideal,of course)
So either the battery isn't ideal or the meters aren't ideal. (Or both aren't ideal).
Then D sounds correct to me.
 

Related to Ammeters and voltmeters in series

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

An ammeter is used to measure the current flowing through a circuit, while a voltmeter is used to measure the voltage across a circuit.

2. Can ammeters and voltmeters be connected in series?

Yes, ammeters and voltmeters can be connected in series as long as they are connected in the correct order. The ammeter should be connected first in the circuit, followed by the voltmeter.

3. How do ammeters and voltmeters affect the circuit they are connected to?

Ammeters have a low resistance, so they can affect the circuit by drawing some current away from it. Voltmeters, on the other hand, have a high resistance, so they have a minimal effect on the circuit.

4. What is the purpose of connecting ammeters and voltmeters in series?

The purpose of connecting ammeters and voltmeters in series is to measure the current and voltage in a circuit accurately. By connecting them in series, the meters are able to measure the actual current and voltage flowing through the entire circuit.

5. Is it possible to connect multiple ammeters and voltmeters in series?

Yes, it is possible to connect multiple ammeters and voltmeters in series. However, it is important to consider the resistance of the meters to ensure that they do not affect the circuit significantly. It is also important to connect them in the correct order to get accurate readings.

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