Magnetic Effects & Magnetism

JEE Main level, single correct, medium

234 of 276

Question 234 of 276

One of the two small circular coils, (none of them having any self - inductance) is suspended with a V-shaped copper wire, with plane horizontal. The other coil is placed just below the first one with plane horizontal. Both the coils are connected in series with a dc supply. The coils are found to attract each other with a force.
Which one of the following statements is incorrect?

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Answer: (D) Force is proportional to d−2\mathrm{d}^{-2}

As the force between the two coils is attractive hence currents in the coil must be in the same direction and the force, F∝I1I22πd\mathrm{F} \propto \frac{\mathrm{I}_1 \mathrm{I}_2}{2 \pi \mathrm{d}}
where I1I_1 and I2I_2 are the currents flowing through the coils.

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