Q.

A rigid wire consists of a semicircular portion of radius R and two straight sections. The wire is partially immersed in a perpendicular magnetic field B=B0j^ as shown in the figure. The magnetic force on the wire if it has a current i is              [2024]

1 -2iBRj^  
2 2iBRj^  
3 -iBRj^  
4 iBRj^  

Ans.

(1)

Note: Direction of magnetic field is in +k^

Force on current carrying wire,

F→=iℓ→×B→

Here, ℓ=2R

⇒F→=-2iRBj^