What is the Internal Resistance of a Cell?

[huey910]

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?

 

[gneill]

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?