Q 12-06-016NEETJEE MainMedium
A conducting rod of length $0.5$ m slides at $2$ m/s on two parallel rails joined by a $1\ \Omega$ resistor, in a field of $1$ T perpendicular to the plane. The force needed to keep the rod moving at constant speed is (neglect other resistances)
Answer: (B) $0.5$ N
Concept. At constant speed the applied force balances the magnetic drag $BIl$, with $I = \dfrac{Blv}{R}$.
Step 1. Emf and current. $\varepsilon = 1 \times 0.5 \times 2 = 1$ V; $I = 1$ A.
Step 2. Force. $F = BIl = 1 \times 1 \times 0.5 = 0.5$ N.
Answer. $0.5$ N (Option B).
Solution by Sreeraj P, M.Sc Physics