AS Physics Cwk: "Classic" Resistance of a wire Watch

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Hi, I'm doing the good old resistance of a wire coursework. investigating how length of wire effects resistance. The circuit I'm using is a 6V battery, ammeter, "the wire" and a variable resistor in series, with a volt meter in parallel across "the wire".

My teacher says we should keep the current under 0.5 A to minimise heating effects. However, I was thinking wouldn't it be more important to keep power dissipated constant, P=(I^2)*R=V/I. So by controlling V and I using the variable resistor to keep the power constant for each different length. However, this causes two problems in my understanding:

1.) What therefore is the need to repeat and average readings for each length. Which is a essential component of the AQA mark scheme.

2.) By controlling V and I you will get a constant value of P, however is that P dissipated or P of the circuit i.e. rate at which chemical energy is converted to electrical.

I know this isn't a difficult coursework to do and I think my understanding of the above is probably incorrect. So could any one explain the correct way to carry out the experiement and what's wrong with the way I'm thinking about things.

I would really appreciate it! Thanks!
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