Find emf and the inner resistor of the battery

[prishila]

Homework Statement

When the resistor is R1, in the circle there is the intensity I1 and when the resistor is R2, the intensity becomes I2.Find emf and the inner resistance.[/B]

Homework Equations

I=emf/R+r

The Attempt at a Solution

I1=efm/R1+r
I2=efm/R2+r
efm is equal
I1*(R1+r)=I2(R2+r)
r=(I2R2-I1R1)/(I1-I2)
And how can I find emf?

 

[BvU]

Can I rephrase the problem statement as :
With a resistor R1 connected to a battery, the current is I1.
With a resistor R2 connected to a battery, the current is I2.
Find emf and the internal resistance.
Your equation requires brackets: $I_i = emf / (R_i + r_{internal})$

So you have two equations with two unknowns: $emf$ and $r_{internal}$. Can you write them down and post ?

And: the mentor will move this thread to introductory physics homework.

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[prishila]

Can I rephrase the problem statement as :
With a resistor R1 connected to a battery, the current is I1.
With a resistor R2 connected to a battery, the current is I2.
Find emf and the internal resistance.
Your equation requires brackets: $I_i = emf / (R_i + r_{internal})$

So you have two equations with two unknowns: $emf$ and $r_{internal}$. Can you write them down and post ?

And: the mentor will move this thread to introductory physics homework.

--

Here's what I did
efm=I1*(R1+r)=I2*(R2+r)
I1*(R1+r)=I2*(R2+r)
I1/I2=(R2+r)/(R1+r)
I1R1+I1r=R2I2+I2r
r(I1-I2)=R2I2-I1R1
r=(R2I2-I1R1)/(I1-I2)
I replaced R with what I found and it results
efm=I1I2(R2-R1)/(I1-I2)
Did I find efm and r correctly?

 

[cnh1995]

efm=I1/(R1+r)=I2/(R2+r)

V=IR and not I/R.

 

[prishila]

V=IR and not I/R.

You're right. i corrected it

 

[cnh1995]

I1/I2=(R2+r)/(R1+r)
I1R1+I1r=R2I2+I2r
r(I1-I2)=R2I2+I1R1

Check the 3rd equation.

 

[prishila]

Check the 3rd equation.

Corrected

 

[cnh1995]

Here's what I did
efm=I1*(R1+r)=I2*(R2+r)
I1*(R1+r)=I2*(R2+r)
I1/I2=(R2+r)/(R1+r)
I1R1+I1r=R2I2+I2r
r(I1-I2)=R2I2-I1R1
r=(R2I2-I1R1)/(I1-I2)
I replaced R with what I found and it results
efm=I1I2(R2-R1)/(I1-I2)
Did I find efm and r correctly?

Looks correct!