How Do You Calculate Resistor Values in a Circuit?

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Homework Help Overview

The discussion revolves around calculating resistor values in a circuit involving a battery with a specified emf and terminal voltage while delivering power to an external load resistor. The problem includes determining the value of the load resistor and the internal resistance of the battery.

Discussion Character

  • Exploratory, Conceptual clarification, Problem interpretation

Approaches and Questions Raised

  • Participants express uncertainty about how to begin solving the problem and seek initial guidance. Some suggest using relevant equations related to voltage, current, and power. Others mention modeling the internal resistance of the battery as a resistor in series with the voltage source and consider drawing a circuit diagram to visualize the components.

Discussion Status

There is an ongoing exploration of the problem with participants sharing equations and concepts that may be relevant. Some guidance has been offered regarding the internal resistance and circuit representation, but no consensus or clear direction has emerged yet.

Contextual Notes

Participants are working within the constraints of a homework assignment, which may limit the information they can share or the methods they can use. There is an emphasis on understanding the relationships between voltage, current, and resistance in the context of the problem.

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Homework Statement


trrttA battery has an emf of 15.0 V. The terminal voltage of the battery is 11.6 V when it is delivering 20.0 W of power to an external load resistor R.
(a) What is the value R?
(b) What is the internal resistance of the battery?


Homework Equations





The Attempt at a Solution


I'm sure how to start this problem. I'm sure I get rolling if I can just get some momentum started. Please Help.
 
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Hopefully these equations will help. If you get stuck just reply.


V = Voltage (Volts)
I = Current (Amps)
R = Resistance (Ohms)
P = Power (Watts)



V = IR (Ohm's Law)

I = V/R (Ohm's Law Rewritten)

P = VI

P = V2/R

P = I2R
 
Last edited:
Keep in mind, the internal resistance of the battery can be modeled as a resistor in series with an ideal voltage source.
 
shinobi12 said:

Homework Statement


trrttA battery has an emf of 15.0 V. The terminal voltage of the battery is 11.6 V when it is delivering 20.0 W of power to an external load resistor R.
(a) What is the value R?
(b) What is the internal resistance of the battery?

Homework Equations



The Attempt at a Solution


I'm sure how to start this problem. I'm sure I get rolling if I can just get some momentum started. Please Help.

Draw a circuit diagram with the external and internal resistor.
You have a voltage divider there don't you?

And you know Power = I2R
 

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