What is the Internal Resistance of a Cell?

AI Thread Summary
The discussion focuses on calculating the internal resistance of a cell based on voltmeter readings across a circuit with a switch and a 2-ohm resistor. When the switch is open, the voltmeter reads 12V, and when closed, it reads 8V, indicating a voltage drop due to internal resistance. The internal resistance is determined to be 1 ohm, which is derived from understanding that the current remains constant in a DC circuit. Participants emphasize the importance of identifying voltage drops and sketching the circuit for clarity. The conversation highlights the relationship between voltage, current, and resistance in determining the internal resistance of the cell.
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Homework Statement


A voltmeter is connected across a cell in a circuit containing a switch and a 2Ohm resistor. When the switch is open, the voltmeter reads 12V. When it is closed, the reading is 8V. Find the internal resistance of the cell.


Homework Equations


I tried to use V=IR - is I constant? does this have to do with voltage drops?


The Attempt at a Solution


the solution is 1Ohm. Why is that?
 
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huey910 said:

Homework Statement


A voltmeter is connected across a cell in a circuit containing a switch and a 2Ohm resistor. When the switch is open, the voltmeter reads 12V. When it is closed, the reading is 8V. Find the internal resistance of the cell.


Homework Equations


I tried to use V=IR - is I constant? does this have to do with voltage drops?
You're dealing with a DC source (a cell) and resistances, so yes, the current I is constant.
Yes, this has to do with voltage drops. Can you identify where voltage drops are occurring and what their values are?

The Attempt at a Solution


the solution is 1Ohm. Why is that?
Isn't that what you need to show?

Have you sketched the circuit as described? With the given information, what expressions can you write for current and potential drops? Can you determine any of the values?
 

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