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

In summary, to solve for the emf and internal resistance of a battery, we can treat the internal resistance as a resistor in series with the battery and use Kirchoff's voltage law to set up equations for the two different circuit configurations. By solving these equations, we can find the values for emf and internal resistance.
  • #1
FlipStyle1308
267
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!
 
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  • #2
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:
  • #3
Would you be able to explain a bit more for step #1? How would my equation(s) be set up?
 
  • #4
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
 

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

1. What is internal resistance?

Internal resistance is the opposition to the flow of electric current within a battery or other electrical component. It is caused by the resistance of the materials used to construct the battery and the chemical reactions that take place within it.

2. How does internal resistance affect the performance of a battery?

The internal resistance of a battery can impact its voltage output and overall performance. As the current flows through the battery, some of the energy is lost to heat due to the internal resistance. This can reduce the battery's voltage, resulting in a decrease in power and a shorter lifespan.

3. What factors can contribute to high internal resistance?

High internal resistance can be caused by a variety of factors, including the materials used to construct the battery, the design of the battery, and the age of the battery. In addition, high temperatures and overcharging can also increase internal resistance.

4. How can internal resistance be measured?

Internal resistance can be measured using a multimeter or other specialized equipment. The most common method is to measure the voltage of the battery under load and then divide it by the current flowing through the battery. This will give the internal resistance value in ohms.

5. How can internal resistance be reduced?

There are several ways to reduce internal resistance in a battery, including using materials with lower resistance for construction, improving the design of the battery to minimize internal resistance, and ensuring proper charging and usage practices. In some cases, a battery with high internal resistance may need to be replaced with a new one to restore optimal performance.

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