Question

The circuit in fig. consists of wires at the top and bottom and identical metal springs at the left and right sides.The wire at the bottom has a mass of 10.0g and is 5.00cm long. The wire is hanging as shown in the figure. The springes stretch 0.500 cm under the weight of the wire, and the circuit has a total resistance of `12.0Omega`. When a magnetic field is turned on the springes stretch an additional 0.300 cm.

The magnitude of magnetic field is
A. `1.2T`
B. `6T`
C. `0.6T`
D. `12T`

Answer 1

Correct Answer - c
`I=epsilon/R=24/12=2A` M

`Magnetic force =IlB sin (pi/2)=2xx5xx10^-2xxB=B/10`
`2kx_1=mg, 2k=(mg)/(x_1) ` and
`2k(x_1+x_2)=mg+IlB`
`2kx_1+2kx_2=mg+IlB`
`(mg)/(x_1) x_2=IlB`
`10xx10^-3xx10xx0.3/0.5=B/10 implies B=600xx10^-3=0.6T`