CGPET 2019 Solved Paper

Magnetic field due to an arc of a circle at the centre is B=(

µ0

4π

)(

i

R

)θ
Magnetic field due to straight wire at point O is zero and the magnetic field due to semicircular loop radius R1 is given by
B1=

µ0i

4k1

(

π

π

)=

µ0i

4R1

Similarly, magnetic field due to semicircular loop of radius R2 is given by B2=

µ0i

4R2

As,R2>R1
Hence, net magnetic field
Bnet =B1−B2=

µ0i

4R1

−

µ0i

4R2

=

µ0i

4

(

1

R1

−

1

R2

)