Calculating EMF and Internal Resistance: A Practical Guide

[Gustavs1337]

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.

 

[cnh1995]

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?

 

[Gustavs1337]

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. I am 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).

 

[cnh1995]

Could you state the exact problem statement?

 

[Gustavs1337]

Circuit consisting of battery, switch, resistance and a voltmeter. We take 2 measurements. One with a resistance of 3 ohms, there's voltage of 3.6 volts. Second with a resistance of 5, there's a voltage of 3.8 volts. Calculate the EMF, internal resistance and short-circuit current(sorry i didnt mention the short circuit current before)

 

[cnh1995]

Circuit consisting of battery, switch, resistance and a voltmeter. We take 2 measurements. One with a resistance of 3 ohms, there's voltage of 3.6 volts. Second with a resistance of 5, there's 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.

 

[Gustavs1337]

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?

 

[Gustavs1337]

Ok i get it now, thanks. I think i can calculate emf and r now from the equations.