IIT JEE , AIEEE Forum - Physics , Magnetism

johri_anshuman

consider a small elementary ring or radius r and thickness dr from the centre of the disc as shown in the fig...

the magnetic field due to this ring is given as

dB = u₀wr²p 2 pi r dr / 4pi (d²+r²)^3/2 where p = sigma

integrating for the limits 0 to R

B = u₀wp/2 ₀

^R r³dr/(d²+r²)^3/2

since d>>r

B = u₀wp/2d³ ₀

^R r³dr

u'll get

B = u₀wpR⁴/8d³

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