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 \( 0.2 \, \text{T} \) parallel to the axis exists everywhere. The emf developed between the centre and the ring is __________ \( \text{mV} \).
Take \( \pi = \dfrac{22}{7} \)
