Measuring the Resistance of a Wire

[Peter G.]

Hi,

First and foremost, I hope this question doesn't sound stupid!

I am doing a lab for school in which I have to measure the resistance of a wire. As part of that, I have to measure the p.d across the wire and the current through it. After collecting my results my teacher said that I should have kept the current constant throughout... He wasn't in today so I couldn't ask him why?

Why should I keep the current constant?

Thanks,
Peter

 

[gneill]

Hi,

First and foremost, I hope this question doesn't sound stupid!

I am doing a lab for school in which I have to measure the resistance of a wire. As part of that, I have to measure the p.d across the wire and the current through it. After collecting my results my teacher said that I should have kept the current constant throughout... He wasn't in today so I couldn't ask him why?

Why should I keep the current constant?

Thanks,
Peter

That will depend upon the details of the lab procedure and how you're expected to handle the collected data for your writeup. Are there particular graphs you're expected to plot?

Note also that if the wire has resistance it'll be generating heat when current flows through it. More current means more heat per unit length. How does resistance vary with temperature for metals? For a given current the steady-state temperature of the wire will be constant (the temperature will settle at a point where the radiated heat = generated heat).

 

[Peter G.]

I am expected to plot a graph of resistance against length. Thanks for the response, I know acknowledge the importance of setting the current constant!