A car battery is placed on a platform balance and its weight appears on the scal

Question

A car battery is placed on a platform balance and its weight appears on the scale. A wire is attached to one terminal and runs below the balance and is attached to the other terminal thus producing a current in the wire. The mass of the battery and wire is .25kg. If the lower straight portion of the wire, only is placed in an external magnetic field of .2T,

(a) Calculate the current needed to make the scale read zero weight.

(b) In what direction does the current flow, clockwise or counterclockwise?

Explanation / Answer

since force on current carrying wire,F = IL x B = ILBsin

in this case, =90, thus F=ILB

L=0.5 m, B=0.2 T, weight on scale,W = 0.25*9.8 = 2.45 N

for making scale read zero, F=W => ILB = W => I = 2.45/(0.5*0.2) = 24.5 A ans(a)

Current should flow clockwise for upward force in wire. ans(b)

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