In the figure below, the two ends of a U -shaped wire of mass m = 9.50 g and len
ID: 1319657 • Letter: I
Question
In the figure below, the two ends of a U-shaped wire of mass m = 9.50 g and length L = 15.0 cm are immersed in mercury (which is a conductor). The wire is in a uniform field of magnitude B = 0.110 T. A switch (unshown) is rapidly closed and then reopened, sending a pulse of current through the wire, which causes the wire to jump upward. If jump height h = 2.70 m, how much charge was in the pulse? Assume that the duration of the pulse is much less than the time of flight. Consider the definition of impulse and its relationship with momentum. Also consider the relationship between charge and current.
Explanation / Answer
F= i . (dL X B)
Impulse = F.dt i dt . (dL X B) = q . (dL X B) = q.* 0.15 *0.11 =0.0165 q (i.dt =q)
Impulse = change in momentum = mv = 0.0165 q
m* sqrt (2gh) =0.0165 q
[9.5 *sqrt (2*9.8*2.7)]/1000 = 0.0165 q
q = 4.19 C