value 4.00 points 1 out of 5 attempts As A current balance is a device to measur

Question

value 4.00 points 1 out of 5 attempts As A current balance is a device to measure magnetic forces. It is constructed from two parallel coils, each with an average radius of14.8 cm. The lower coil rests on a balance; it has 20 turns and carries a constant current of 2.80 A. The upper coil, suspended 0.314 em above the lower coil, has 50 turns and a current that can be varied. The reading of the balance changes as the magnetic force on the lower coil changes. What current is needed in the upper coil to exert a force of 1.46 N on the bottom coil? Ammeter Variable de power supply Wire wrapped- around disk circumference 50 turns 20 turns 0.314 cm Plate on which de nower References

Explanation / Answer

Since the distance between the coils is small compared to the radius of the coils, so we can consider them as 2

long parallel straight wires.

Length of lower loop,

L = N*2*pi*r

L = 20*2*pi*0.148 = 18.59 m

Force on lower coil due to upper coil,

F = B*iL*LL

where B = u0*iu / 2*pi*d

F = (u0*iu / 2*pi*d) * iL*LL

iu = 2*pi*d*F / u0*iL*LL

Put the values,

iu = 2*pi*0.00314*1.46 / 4*pi*10^(-7)*2.8*18.59

iu =  440 A (this is the total current in 50 turns of upper coil)

Current in upper coil in each turn,

i = 440 / 50

i = 8.8 A

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