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**1. Homework Statement**

Ok, you'll have to bare with me on this problem, this topic is not covered as part of my second level education. I think that ye do this in the US though.

You are given a circuit containing a non-ideal power supply, an NTC resistor, an ammeter, a voltmeter, and a switch. The circuit is at room temp. The ammeter and voltmeter are both ideal.

After closing the switch, the temp of the NTC changes, and the voltage across and the current through the NTC are measured at regular intervals until the temp of the NTC remains constant.

You are given a graph of V (in Volts) versus I (in Amps). -> (V, A)

Data points: (0.16, 6.9) (0.25, 6.84) (0.33, 6.9)

**Q. Determine the internal voltage and the internal resistance of the power supply.**

**2. Homework Equations**

Well, since we don't cover this topic, I haven't got the equations straight from a textbook. But, I've come up with the following ideas:

EMF = V + v

and EMF = I(R + r)

and EMF = V + v = I(R + r)

and v = Ir

**3. The Attempt at a Solution**

Well, I'm not completely sure where to go from here. Ah, something just came into my head, using one set of those values, does the internal voltage = internal resistance?

To be honest, I'm stumped. Could someone give me an idea about what to do, the concepts involved, etc.?

Cheers!