KCET 2021 Physics Solved Paper

Magnetic field due to toroid can be given as
(i) In the open space, exterior of a toroid,
B=0 (ii) Inside the toroid,
B=

µ0‌NI

2πT

Here, r=

R1+R2

2

⇒ B=

µ0‌NI

π(R1+R2)

= constant
So, the variations of B with r is correctly depicted in option (d).