LearnHub

Join LearnHub

Community

LearnHub Support

electric current (Question)

raghav sood said – Sat, 19 Sep 2009 04:57:09 -0000 ( Edit Link )

consider a dc circuit with a cell of emf ‘E’ and internal resistance ‘r’ connected to an external resistance ‘R’. let ‘I’ be the current flowing in the circuit. Is the potential differnce across the cell same as that across the external resistance ?

if so power dissipated across the cell = I x I x r Also, power dissipated across the cell = V I Where V is the potential differnce across the external resistance therefore, power dissipated across the cell = (IR) I = I x I x R WHICH IMPLIES r IS ALWAYS EQUAL TO R ?

Actions

Answer

Author: raghav sood; Authority 17

Vote

Current Rating: 0; Rate Up; Rate Down

2 Votes

5 Answers

raj beniwal said – Wed, 23 Sep 2009 07:49:34 -0000 ( Flag Edit Mark / Unmark Best Link )

V=I(R+r) thus power dissipation across the cell is II*(R+r).= i@2R+i@2*r= power disspated across load resistance plus power dissipated across internal resistance of the Cell.

r is very small amount in comparision to R so we neglect this and consider that there is total drop across the load resistance R ohms.
Actions
Reply To This
Author

raj beniwal

Authority 82

Vote

Current Rating

1

Rate Up

Rate Down

1 Total Vote
Post Comments
Add Comment

Your Reply
angadyuvraj said – Wed, 23 Sep 2009 08:41:01 -0000 ( Flag Edit Mark / Unmark Best Link )

i totally agree with Mr RAj Beniwal.wat Mr ragav wrote was individual power dissipated across each resistence n also r is negligible so we cant equate IxIxr=IxIxR bcoz both of them are differnt.

am i clear??
Actions
Reply To This
Author

angadyuvraj

Authority 84

Vote

Current Rating

1

Rate Up

Rate Down

1 Total Vote
Post Comments
Add Comment

Your Reply
dusvijay10 said – Wed, 23 Sep 2009 11:36:30 -0000 ( Flag Edit Mark / Unmark Best Link )

if we neglect the internal resistance of the source then it is same gen p=i^{2r(equivalent)
r(equi)=R+r
so
p=i}2(R+r) if R>>>r then p=i^2R which is potential drop across the external resi
Actions
Reply To This
Author

dusvijay10

Authority 19

Vote

Current Rating

1

Rate Up

Rate Down

1 Total Vote
Post Comments
Add Comment

Your Reply
shalu2009 said – Wed, 23 Sep 2009 13:20:21 -0000 ( Flag Edit Mark / Unmark Best Link )

no,the potential across E is Ir and across R is iR….power dissipated across E is II*r and power dissipated across R is II*R m i right???
Actions
Reply To This
Author

shalu2009

Authority 55

Vote

Current Rating

1

Rate Up

Rate Down

1 Total Vote
Post Comments
Add Comment

Your Reply
deepa mittal said – Tue, 29 Sep 2009 08:13:34 -0000 ( Flag Edit Mark / Unmark Best Link )

The potential difference across external resistance when circuit is closed is called terminal potential difference. V = E – Ir

The potential difference at the terminals of the source when circuit is open, is called terminal potential different. E = V (Ir = 0)
Actions
Reply To This
Author

deepa mittal

Authority 608

Vote

Current Rating

1

Rate Up

Rate Down

1 Total Vote
Post Comments
Add Comment

Your Reply