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# Confusing question help

1. Question: Calculate the uncertainty in the resistance of a bulb. The equation is R=V/I and the following measurements were taken:
Potential Difference = 1.1 V
Current = 0.4 A
2. (Original post by XtrJ)
Question: Calculate the uncertainty in the resistance of a bulb. The equation is R=V/I and the following measurements were taken:
Potential Difference = 1.1 V
Current = 0.4 A
This question is checking whether you understand the connection between uncertainty and the number of significant figures used.

1.1 V has 2sf
0.4 A has 1 sf - so it could be anywhere between 0.350 and 0.449

trailing zeros AFTER the decimal point *are significant figures* - if you measured the current to higher precision you could write 0.40 (i.e. 2sf) which would mean it was between 0.395 and 0.404

the rules for combining uncertainties at A level are in stonebridge's sticky http://www.thestudentroom.co.uk/show....php?t=2661762

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