Physics Question from JEE Main 2023 · 15 April, Shift 1

A $20 \, \text{cm}$ long metallic rod is rotated with $210 \, \text{rpm}$ about an axis normal to the rod passing through its one end. The other end of the rod is in contact with a circular metallic ring. A constant and uniform magnetic field of $0.2 \, \text{T}$, parallel to the axis, exists everywhere. The emf developed between the centre and the ring is _____ mV. (Take $\pi = \dfrac{22}{7}$)