Question

A wire PQR is bent as shown in figure and is placed in a region of uniform magnetic field B. The length of PQ = QR = I. A current I ampere flows through the wire as shown. The magnitude of the force on PQ and QR will be

• A. BIl, 0
• B. 2BIl, 0
• C. 0, BIl
• D. 0, 0

Answer 1

Answer: (C)

The Lorentz force acting on the current carrying conductor in the magnetic field is $F=IBl\sin \theta$ Since, wire PQ is parallel to the direction of magnetic field, then $\theta =0,$ $\therefore$ $F_{PQ}=IBl\sin 0{}^{\circ }=0$ Also, wire QR is perpendicular to the direction of magnetic field, then $\theta =90{}^{\circ }.$ $\therefore$ $F_{QR}=IBl\sin 90{}^{\circ }=IBl$