Extension in Spring due to Magnetic force!

Electricity and Magnetism Level 3

The circuit in figure consists of wires at the top and bottom and identical metal springs as the left and right sides. The wire at the bottom has a mass of $10 \text{ g}$ and is $5 \text{ cm}$ long. The wire is hanging as shown in the figure. The spring stretch $0.5 \text{ cm}$ under the weight of the wire and the circuit has a total resistance of $12 \Omega$ . When the lower wire is subjected to a static magnetic field, the springs stretch an additional $0.3 \text{ cm}$ . The magnetic field is?

1.2 T and directed out of page None of These 0.6 T and directed into the plane of page 1.2 T and directed into the plane of page 0.6 T and directed out of page

1 solution

Nishant Rai
May 27, 2015

Draw The FBD of the system.

When magnetic field is on, in equilibrium, $K\Delta L = mg + BiL$

$\large \Rightarrow B = \frac{K\Delta L - mg}{iL} = \frac{(\frac{mg\Delta l }{\Delta l_0}-mg)}{\frac{V}{R}L}$ (where $\Delta l_0$ is the expansion when no magnetic field is on.)

Magnetic field must be of out of the page as magnetic force is downward.

Should`nt the magnetic field out of the plane. As current moves from higher to lower potential and current will be in right direction so using Fleming's rule force is downward . Magnetic field out of paper

Kyle Finch - 6 years ago

Plz reply @Nishant Rai

Kyle Finch - 6 years ago

you're correct, while writing the solution, i missed "out of the page". Sorry for the trouble.

@Kyle Finch

Nishant Rai - 6 years ago

Extension in Spring due to Magnetic force!

1 solution

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