How Do You Calculate EMF and Internal Resistance in a Circuit?

Click For Summary

Homework Help Overview

The discussion revolves around calculating the electromotive force (emf) and internal resistance of a battery in a circuit involving different resistors. The problem presents two scenarios with specified currents and resistances, prompting participants to explore how to incorporate internal resistance into their calculations.

Discussion Character

  • Exploratory, Conceptual clarification, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to understand how to apply the equation V = IR while considering internal resistance. Some participants suggest treating the internal resistance as an additional resistor in series with the battery and propose drawing circuit diagrams for clarity. Others inquire about the setup of equations based on the circuit diagrams and the application of Kirchhoff's voltage law.

Discussion Status

The discussion is ongoing, with participants providing guidance on how to approach the problem. There is a focus on drawing circuit diagrams and setting up equations, but no consensus has been reached on the specific equations or methods to use.

Contextual Notes

Participants are working under the constraints of the problem as presented, with specific resistor values and currents given. There is an emphasis on understanding the relationship between emf, internal resistance, and the overall circuit behavior.

FlipStyle1308
Messages
264
Reaction score
0
Here is the question I need to solve:

A battery has an emf E and an internal resistance r. When the battery is connected to a 25 ohm resistor, the current through the battery is 0.75 A. When the battery is connected to a 53 ohm resistor, the current is 0.45 A. Find the emf of battery and its internal resistance.

Okay, so I have a feeling I will be using the equation V = IR, but I don't knnow how to incorporate an internal resistance into the equation or approach. Can someone please help me outline the steps to solve this? Thanks!
 
Physics news on Phys.org
1. Treat the internal resistance as a resistor (r) in series with the battery (E).
2. Draw the circuit diagram for both cases.
3. Solve the two circuits - write down the two equations.
4. Solve for the 2 unknowns from the 2 equations.
 
Last edited:
Would you be able to explain a bit more for step #1? How would my equation(s) be set up?
 
FlipStyle1308 said:
Would you be able to explain a bit more for step #1? How would my equation(s) be set up?
You do not set up the equation until you have a circuit diagram. Once you draw the circuit as described in #1, you set up the equation using Kirchoff's voltage law (which is a fancy extension of Ohm's law): algebraic sum of all EMFs = algebraic sum of all voltage drops across resistors (these voltage drops calculated by Ohm's Law).

http://en.wikipedia.org/wiki/Kirchhoff's_circuit_laws
 

Similar threads

High School Troubleshooting Battery Internal Resistance Measurements
  • · Replies 105 ·
4
Replies
105
Views
13K
Internal Resistance of the Battery - Ohmic Resistance
  • · Replies 21 ·
Replies
21
Views
3K
How to solve for EMF and internal resistance in a circuit?
  • · Replies 8 ·
Replies
8
Views
4K
Undergrad Equation for the Internal Resistance of a Battery
  • · Replies 5 ·
Replies
5
Views
3K
Circuit with potential difference across battery being zero?
  • · Replies 3 ·
Replies
3
Views
2K
Unraveling the Mystery of EMF Internal Resistance
  • · Replies 2 ·
Replies
2
Views
2K
Calculating current with and without internal resistance
  • · Replies 6 ·
Replies
6
Views
3K
Batteries in series, parallel, and internal resistance
  • · Replies 24 ·
Replies
24
Views
6K
Why do the headlights on the car become dim when the car is starting?
  • · Replies 4 ·
Replies
4
Views
2K
Potentiometer and EMFs with internal resistance
  • · Replies 4 ·
Replies
4
Views
3K