a mild steel bar of length 10cm and width of 10mm is extended by 0.01 mm. Which of the following is equal to the change in width of the bar.(The Poisson's ratio of mild steel is 0.31)

Question

a mild steel bar of length 10cm and width of 10mm is extended by 0.01 mm. Which of the following is equal to the change in width of the bar.(The Poisson's ratio of mild steel is 0.31)
A	  3.1x10-4mm
B	 -3.1x10-4mm
C	 3.1x10-5mm
D 	-3.1x10-5mm