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JEE Advanced · Physics · 20. Magnetism & Current

Two concentric circular loops, one of radius R and the other of radius 2R, lie in the xy-plane with the origin as their common center, as shown in the figure. The smaller loop carries current I1 in the anti-clockwise direction and the larger loop carries current I2 in the clockwise direction, with I2>2I1. Bx,y denotes the magnetic field at a point x,y in the xy-plane. Which of the following statement(s) is (are) correct?

  1. A Bx,y is perpendicular to the xy-plane at any point in the plane
  2. B Bx,y depends on x and y only through the radial distance r=x2+y2
  3. C Bx,y is non-zero at all points for r<R
  4. D Bx,y points normally outward from the xy-plane for all the points between the two loops
Verified Solution

Answer & Solution

Correct Answer

(B) Bx,y depends on x and y only through the radial distance r=x2+y2

Step-by-step Solution

Detailed explanation



(A) Magnetic field at the plane of the ring is perpendicular to the plane. However, they bend as they move forward.



(B) By symmetry, we can say thatBwill be same at all the points having the same radial distance. soBx,ywill depend only the radial distancer=x2+y2



(C)Bnetcentre=μ0I222R-μ0I12R=μ04RI2-2I1Since,I2>2I1soBnetat the centre will be non-zero indirection, But at some other point,Bnetmay be zero.

From the graph, it is clear thatBnet=0for some value ofr0,R. Sooption (C) is incorrect





(D) For the graph, it is clear thatB=-veindirection forrRto2R, so option D is also incorrect.
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