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JEE Main 2020 (2 Sep, Shift 2) · Current Loop as a Magnetic Dipole

Current Loop as a Magnetic Dipole question from JEE Main 2020 (2 Sep, Shift 2)

Q63JEE Main 2020 · 2 SEP · SHIFT 2Difficult

Current Loop as a Magnetic Dipole

A wire carrying current I is bent in the shape ABCDEFA as shown, where rectangle ABCDA and ADEFA are perpendicular to each other. If the sides of the rectangles are of lengths a and b, then the magnitude and direction of magnetic moment of the loop ABCDEFA is

Figure

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Answer: (c)

  1. Split the wire into two loops ABCDA and ADEFA; the common side AD carries opposite currents and cancels.
  2. ABCDA lies in the horizontal (XY) plane, area abab: m⃗1=abI k^\vec m_1 = abI\,\hat k.
  3. ADEFA lies in the vertical (XZ) plane, area abab: m⃗2=abI j^\vec m_2 = abI\,\hat j.
  4. m⃗=abI(j^+k^)\vec m = abI(\hat j + \hat k), magnitude 2 abI\sqrt2\,abI along j^2+k^2\frac{\hat j}{\sqrt2} + \frac{\hat k}{\sqrt2}.
  5. So the answer is (c).
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