IIT JEE Advanced 2009 Paper 2

The segments PQ and PR, in the triangle shown here, cannot produce

→

B

at point P since point P lies on them. Here, only QR creates

→

B

at point P.
Applying BP =

µ0i

4πR

(cosϕ1+cosϕ2) , where
ϕ1 = 53° and ϕ2 = 37°, we get the magnitude of the magnetic field as follows:
BP =

µ0I

4π(4πsin37°)

(cos 53° + cos 37°)
=

µ0I

16π×( 3 5 )

(

3x

5x

+

4x

5x

)
= 5µ0

I

48πx

(

7

5

) =

7µ0I

48πx

= k(

µ0I

48πx

)
where k = 7.