6PH07/01 (Physics Unit 3B) January 2013 Question

[Mesoud]

Sorry if this might seem meaningless, but I'm having trouble solving question 3 in this particular exam paper.

"In an experiment to measure the breaking stress of a wire the diameter of the wire is measured with a micrometer.

Which of the following procedures would not be good practice?
A) Checking for zero errors
B) Repeating the reading three times
C) Rotating the micrometer between readings
D) Using a second piece of the wire to check the diameter"

The correct answer is supposedly D, but I have no clue why. When I first came across this question, I answered C as, at the time, it made the most sense to me.
Can anyone help explaining the reasoning behind the answer?
Thanks in advance

 

[Mesoud]

I'd really appreciate it if someone could maybe explain why the answer turned out to be D.

 

[Mesoud]

I'm sorry, but this is really important. I'd love help ASAP

 

[tochina_to]

C is wrong because changing the micrometer's orientation while measuring a wire is indeed a good practice. As for comparing a wire's diameter with another isn't very accurate because mainly both diameters are quite small and the difference might not be very visible. Hope this cleared it up a bit though. :]y

 

[Mesoud]

Thanks for the help