JEE PYQ: Magnetic Effects Of Current Question 44
Question 44 - 2019 (09 Jan 2019 Shift 1)
An infinitely long current carrying wire and a small current carrying loop are in the plane of the paper as shown. The radius of the loop is $a$ and distance of its centre from the wire is $d$ ($d \gg a$). If the loop applies a force $F$ on the wire then:
(1) $F = 0$
(2) $F \propto \left(\frac{a}{d}\right)$
(3) $F \propto \left(\frac{a^2}{d^3}\right)$
(4) $F \propto \left(\frac{a}{d}\right)^2$
Show Answer
Answer: (3) $F \propto \left(\frac{a^2}{d^3}\right)$
Solution
The loop acts as a dipole. Force $F = M\frac{dB}{dx} \propto \frac{a^2}{d^3}$.
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