Answer:
Option D
Explanation:
B at centre of a circle = μ0I2R
B at centre of a square
=4×μI4π.l2[sin45∘+sin45∘]
=4√2μI2πl
Now, R=L2π and l=L4
(As L=2πR=4l )
Where , L= length of wire
BA=μ0I2.L2π=πμ0IL=π[μ0IL]
BB=4√2μ0I2π(L4)
=8√2μ0IπL=8√2π[μ0IL]
BABB=π2:8√2