EMF and internal resistance

  • #1

Homework Statement


I need to calculate EMF and internal resistance from the given resistance and voltage.
R = 3 ohms
U = 3,6 V
EMF- ?
I0 - ?
r - ?

Homework Equations


I = U/R
EMF = A/q
I = EMF/R+r
I0 = EMF/r

The Attempt at a Solution


I = 3,6/3 = 1,2 A
I = EMF/R+r
1,2= EMF/3+r
^ I hit a wall there, don't know whether to consider EMF to be the same as Voltage or not. Help please.
 

Answers and Replies

  • #2
cnh1995
Homework Helper
Gold Member
3,421
1,145

Homework Statement


I need to calculate EMF and internal resistance from the given resistance and voltage.
R = 3 ohms
U = 3,6 V
EMF- ?
I0 - ?
r - ?

Homework Equations


I = U/R
EMF = A/q
I = EMF/R+r
I0 = EMF/r

The Attempt at a Solution


I = 3,6/3 = 1,2 A
I = EMF/R+r
1,2= EMF/3+r
^ I hit a wall there, don't know whether to consider EMF to be the same as Voltage or not. Help please.
Given data is insufficient. Are you sure you posted all the given quantities?
 
  • #3
Given data is insufficient. Are you sure you posted all the given quantities?
There is a second measurement which is with a resistance of 5 and a voltage of 3,8. Im not sure if that helps. Also the electric circuit consists of a switch, battery, resistance and an internal voltmeter ( not sure about the internal part but it is on the inside of the circuit and not the outside).
 
  • #4
cnh1995
Homework Helper
Gold Member
3,421
1,145
Could you state the exact problem statement?
 
  • #5
Circuit consisting of battery, switch, resistance and a voltmeter. We take 2 measurements. One with a resistance of 3 ohms, theres voltage of 3.6 volts. Second with a resistance of 5, theres a voltage of 3.8 volts. Calculate the EMF, internal resistance and short-circuit current(sorry i didnt mention the short circuit current before)
 
  • #6
cnh1995
Homework Helper
Gold Member
3,421
1,145
Circuit consisting of battery, switch, resistance and a voltmeter. We take 2 measurements. One with a resistance of 3 ohms, theres voltage of 3.6 volts. Second with a resistance of 5, theres a voltage of 3.8 volts. Calculate the EMF, internal resistance and short-circuit current(sorry i didnt mention the short circuit current before)
Ok. Start by drawing a circuit diagram.
Calculate current I in both the cases using Ohm's law.
I = EMF/R+r
You know R and I for two measurements. You havd two unknowns Emf and r.
Form two simultaneous equations with two unknowns from the given measurements and solve them.
 
  • #7
Do you want me to show you the diagram? I cannot show you but i have it drawn. The I in both cases are 1.2 and 0.76 ohms.
1.2=x:(3+y)
0.76=x:(5+y) do you mean like this? How to solve them? Do i use the sum method or something?
 
  • #8
Ok i get it now, thanks. I think i can calculate emf and r now from the equations.
 

Related Threads on EMF and internal resistance

  • Last Post
Replies
7
Views
23K
  • Last Post
Replies
4
Views
2K
Replies
6
Views
8K
Replies
4
Views
1K
Replies
1
Views
1K
Replies
11
Views
10K
Replies
3
Views
1K
Replies
9
Views
5K
Replies
1
Views
1K
Replies
4
Views
1K
Top