• Support PF! Buy your school textbooks, materials and every day products Here!

Infinite resistance of a Voltmeter

  • Thread starter shehri
  • Start date
  • #1
30
0
While studying about 'Potentiometer' it's said :
"The resistance of the voltmeter be large compared to the circuit resistance across which the voltmeter is connected.Otherwise an appreciable current will flow through voltmeter which will alter the circuit current & the P.D to be measured". Can any body explain this concept?.Thanks.
 
Last edited:

Answers and Replies

  • #2
Ouabache
Science Advisor
Homework Helper
1,340
7
The concept is actually straight forward. You need to show some thought about your question before we can help you. (see post)

If you are truly lost, you might begin by defining some of the terms or if it is a measuring device, how do you normally use this in the lab. Have you done any research about this, on the web? (hint: use search engines)..
 
Last edited:
  • #3
194
0
Think of two circuits each with a battery and a two equal resistors of say 1kohm, one where you are measuring the voltage across a resistor with a high resistance voltmeter say 1Mohm and one where you measure with a low resistance voltmeter say 1ohm. Draw out the circuits and see if you can work out what the voltage measured in each case would be and what the actual voltage should be.
 
  • #4
mjsd
Homework Helper
726
3
While studying about 'Potentiometer' it's said :
"The resistance of the voltmeter be large compared to the circuit resistance across which the voltmeter is connected.Otherwise an appreciable current will flow through voltmeter which will alter the circuit current & the P.D to be measured". Can any body explain this concept?.Thanks.
Because "an observer disturbs the system he/she is trying to observe", it is important to include a measuring device in a such way that only minimal change to the original system results. In the voltmeter case, you are providing the current an alternative pathway to flow once you have introduced the voltmeter in the circuit. Hence, in order to minimise the amount of currrent using this path (created by the inclusion of the voltmeter) you want the resistance of the voltmeter to be very large compared to the circuit component it is measuring. Higher resistance means that most of the current will follow the original path and hence leads to minimal change to the circuit conditions.
 
  • #5
Ouabache
Science Advisor
Homework Helper
1,340
7
I know both of you, are trying to be helpful to shehri, and you have not earned "homework helper" badges yet. It would be more helpful to the person asking the question, to show they have given some thought to them and not just seeking answers from the PF community.

You are encouraged to read this sticky note which outlines what is expected of posters to the homework section.
 
  • #6
30
0
Thanks for clearing me about 'infinite resistance' in a simple manner.Especially 'mjsd'.Thanks once again.
 

Related Threads on Infinite resistance of a Voltmeter

  • Last Post
Replies
3
Views
2K
  • Last Post
2
Replies
26
Views
3K
  • Last Post
Replies
6
Views
609
  • Last Post
Replies
1
Views
2K
Replies
25
Views
1K
  • Last Post
Replies
14
Views
21K
Replies
5
Views
12K
  • Last Post
Replies
14
Views
669
  • Last Post
Replies
4
Views
25K
Replies
3
Views
606
Top