1)

Two identical wires A and B, each of length l, carry the same current I. Wire A is bent into a circle of radius R and wire B is bent to form a square of side a. If BA and BB are the values of the magnetic field at the centers of the circle and square respectively. then the ratio BABB is


A) π28

B) π2162

C) π216

D) π282

Answer:

Option D

Explanation:

B at centre of a circle =  μ0I2R

B at centre of a square 

     =4×μI4π.l2[sin45+sin45]

     =42μI2πl

Now, R=L2π   and   l=L4

                                                                 (As L=2πR=4l )

 Where , L= length of wire

   BA=μ0I2.L2π=πμ0IL=π[μ0IL]

  BB=42μ0I2π(L4)

=82μ0IπL=82π[μ0IL]

    BABB=π2:82