# Find Internal Resistance From 2 Circuits w/ The Same Battery

• Aleena753
In summary, the problem involves a battery with an emf of 60 V and an internal resistance connected to two different external resistances. The first external resistance is 10 ohms and the power lost inside the battery is 50w. The second external resistance is 4.0 ohms and the power loss is 200w. The goal is to find the internal resistance of the battery. Using the equations V=IR and P=V^2/R, we can find the voltage across the external resistor to be 22.36 V and the current to be 2.23 A. However, this calculation is incorrect as it does not take into account the power dissipated in the battery. To find the correct internal resistance
Aleena753

## Homework Statement

A battery with an emf of 60 V and an internal resistance (r) is connected to a 10 ohm external resistance. The power lost inside the battery is 50w. The same battery is then connected to a 4.0 ohm resistance. The power loss is 200w. What is the internal resistance of the battery?

V = emf - Irint

P= VI

V= IR

P=I^2R

P= V^2/R

## The Attempt at a Solution

P= V^2/R
V= √ PR
V= √50 x 10
V= 22.36 V

I= V/R
= 22.36/ 10
= 2.23 A
Rint= emf - V/ I
Rint= 60 - 22.3/ 2.23
= 16.9 ohms

This is obviously wrong and I didn't even incorporate the second circuit yet. I'm pretty sure I could finish this question if I knew how to start. Any help is appreciated :)

Last edited:

Your calculation of V is incorrect. 50w is the power dissipated in the battery yet you used the value of the external resistor.

Note there is a difference between "power delivered" by the battery and "power dissipated" by the battery.

## 1. How do I find the internal resistance of a circuit with the same battery?

To find the internal resistance of a circuit, you will need to measure the voltage drop across the circuit and the current flowing through the circuit. Once you have these values, you can use Ohm's law (V=IR) to calculate the internal resistance.

## 2. What equipment do I need to find the internal resistance?

You will need a voltmeter to measure the voltage drop and an ammeter to measure the current. It is also helpful to have a battery, wires, and resistors to set up the circuit.

## 3. Can I use any battery to find the internal resistance?

Yes, you can use any battery as long as it has a known voltage. However, it is best to use a battery with a relatively high voltage (such as a 9V battery) to get more accurate results.

## 4. What is the purpose of finding the internal resistance?

Finding the internal resistance of a circuit can help you understand the behavior of the circuit and identify any potential issues. It can also be used to calculate the power dissipated by the internal resistance and the efficiency of the circuit.

## 5. Can I find the internal resistance of a circuit with more than one battery?

Yes, you can find the internal resistance of a circuit with multiple batteries by using the same method as with a single battery. However, the calculations may be more complex and the results may not be as accurate due to the added complexity of the circuit.

• Introductory Physics Homework Help
Replies
42
Views
1K
• Introductory Physics Homework Help
Replies
8
Views
1K
• Introductory Physics Homework Help
Replies
3
Views
241
• Introductory Physics Homework Help
Replies
4
Views
257
• Introductory Physics Homework Help
Replies
8
Views
12K
• Introductory Physics Homework Help
Replies
24
Views
4K
• Introductory Physics Homework Help
Replies
6
Views
1K
• Introductory Physics Homework Help
Replies
14
Views
2K
• Introductory Physics Homework Help
Replies
11
Views
5K
• Introductory Physics Homework Help
Replies
2
Views
1K