Ranking the Loops

A long straight wire carries current out of the page. Three loops are shown. If the integral in each case is carried out by going counter-clockwise around the loop, rank the loops by the value of
Bdl , from largest to smallest.

  1. 1>2>3
  2. 1=2=3
  3. 3>2>1
  4. 1>2 but we can't say for sure where 3 fits in
  5. 1=2 but we can't say for sure where 3 fits in
  6. 2>1 but we can't say for sure where 3 fits in















Ampere's Law says the Bdl is proportional to the current passing through the loop. Each loop encloses the same current, so 1=2=3.