Solving for Resistance and EMF in a Circuit

In summary: It's simple algebra. Distribute I2 on the right side into the parenthesis. That gives you one R term on the left and one R term on the right, with the additional R1*I2 term on the right. Just move the R term from the right side to the left (you do know how to do that, right?), and then finish solving for R all by itself.R*(2.77) = R*(1.81) + (27.39)
  • #1
BuBbLeS01
602
0

Homework Statement



2d7hlhc.jpg


What is the resistance R? (R1=15.13 Ω, I1=2.77 mA , I2=1.81 mA. Give answer in Ω.)
What is the emf of the battery?

Homework Equations



I = E/R

The Attempt at a Solution



How do I solve this with the batteries EMF?
 
Physics news on Phys.org
  • #2
Write 2 equations with the two unknowns (V and R), then solve for both.

And shrink that picture!
 
  • #3
Ok let me see what I can come up with...
How do you shrink it? I did it on tinypic.com
 
  • #4
E = -v1 - V2
E = Ir1 + Ir2
R = E/i
 
  • #5
BuBbLeS01 said:
Ok let me see what I can come up with...
How do you shrink it? I did it on tinypic.com

With Paint or other figure manipulation/drawing programs, you can choose to "Save As" and specify the resolution.
 
  • #6
Are those the right equations? I am not seeing how to solve this?
 
  • #7
BuBbLeS01 said:
E = -v1 - V2
E = Ir1 + Ir2
R = E/i

Write one equation for the current and voltage in the middle branch, and one equation for the current and voltage in the right branch.
 
  • #8
MIDDLE BRANCH:
R = E/I

RIGHT BRANCH:
R = E/I1 + I2

That doesn't look right??
 
  • #9
BuBbLeS01 said:
MIDDLE BRANCH:
R = E/I

RIGHT BRANCH:
R = E/I1 + I2

That doesn't look right??

Why are you not using the names of the resistors in the figure? There are two resistors in the right branch, correct? And current J1 flows in the left branch, and J2 flows in the right branch. Both branches have the same voltage across them, correct?

Take your time and think it out. I need to bail -- you'll get it (or more help may stop by if you have more questions).
 
  • #10
MIDDLE BRANCH:
R = E/I1

RIGHT BRANCH:
R + R1= E/I2

Is that right?
 
  • #11
Ok so I think I got it...I just set them equal to each other and I get...
I1 * R = (R + R1) * I2
But for some reason I don't know how to solve for R! I can't figure it out...very sad...please help me! I have tried all sorts of things and I am not getting anywhere...
 
  • #12
can anyone help me with this part?
 
  • #13
I1 * R = (R + R1) * I2
Substitute the values of I1, I2 and R1 and solve for R
 
  • #14
Thats what I am trying to do but I can't figure out how to get the R by itself on one side since there are 2 of them. I always end up with R/R which is just 1. Its not making sense to me.
 
  • #15
Do you already know what the answer is suppose to be? We use to get the solution to some of our problems, but had to show the work in getting to it.

Do you end up with R*(2.77) = R*(1.81) + (27.39) ?
 
  • #16
No I don't know what the answer should be
 
  • #17
BuBbLeS01 said:
Ok so I think I got it...I just set them equal to each other and I get...
I1 * R = (R + R1) * I2
But for some reason I don't know how to solve for R! I can't figure it out...very sad...please help me! I have tried all sorts of things and I am not getting anywhere...

It's simple algebra. Distribute I2 on the right side into the parenthesis. That gives you one R term on the left and one R term on the right, with the additional R1*I2 term on the right. Just move the R term from the right side to the left (you do know how to do that, right?), and then finish solving for R all by itself.

Please try again, and show each of your steps here.
 

FAQ: Solving for Resistance and EMF in a Circuit

What is resistance?

Resistance is a measure of how difficult it is for electric current to flow through a material. It is measured in ohms (Ω) and is represented by the symbol R.

What is EMF?

EMF stands for electromotive force and it is the force that causes electric current to flow in a circuit. It is measured in volts (V) and is represented by the symbol E.

How do I calculate resistance?

Resistance can be calculated using Ohm's Law, which states that resistance is equal to the voltage (V) divided by the current (I). This can be written as R = V/I. Alternatively, you can also use the formula R = ρl/A, where ρ is the resistivity of the material, l is the length of the material, and A is the cross-sectional area of the material.

How do I calculate EMF?

EMF can be calculated using the formula E = I*R, where I is the current flowing through the circuit and R is the resistance. It can also be calculated using the formula E = I*(r + R), where r is the internal resistance of the power source.

What is the difference between series and parallel circuits?

In a series circuit, all components are connected in a single loop, meaning that the current is the same at every point in the circuit. In a parallel circuit, components are connected in multiple branches, meaning that the current is divided between the branches. This affects how resistance and EMF are calculated in each type of circuit.

Similar threads

Find emf and the inner resistor of the battery
Replies
7
Views
2K
Circuit with potential difference across battery being zero?
Replies
3
Views
781
Calculating EMF and Load Resistance for a Motor
Replies
11
Views
2K
Internal resistance of the battery and energy transformed
Replies
14
Views
2K
Resistance of the resistor and voltmeter's readings
Replies
25
Views
3K
Circuit analysis: Six resistors and two batteries
Replies
1
Views
2K
How Do You Calculate the Resistance of a Voltmeter?
Replies
6
Views
2K
Finding internal resistance & EMF of a battery in a circuit
Replies
11
Views
5K
How to solve this chain with Kirchhoff's laws?
Replies
18
Views
2K
Why do the headlights on the car become dim when the car is starting?
Replies
4
Views
983

Hot Threads

Recent Insights

Back
Top