MCQ
Two long parallel horizontal rails, a distance $l$ apart and each has a resistance $\lambda$ per unit length are joined at one end by a resistance $R$. A perfectly conducting rod $MN$ of mass $m$ is free to slide along the rails without friction. There is a uniform magnetic field of induction $B$ normal to the plane of paper and directed into the paper. A variable force $F$ is applied to the rod $MN$ such that, as the rod moves, a constant current $i$ flows through $P$. The applied force $F$ as function of distance $x$ of the rod from $R$ is
- A$i\,lB-\frac{2m \lambda i^2}{B^2 l^2}(R + 2 \lambda x)$
- B$i\,lB+ \frac{4m \lambda i^2}{B^2 l^2}(R - 2 \lambda x)$
- ✓$i\,lB+ \frac{2m \lambda i^2}{B^2 l^2}(R + 2 \lambda x)$
- Dnone of these
