A conductor ACDG consists of a straight segment AC = 0.5m and a semi-circular arc CDG of radius a = 20cm. A uniform vertical magnetic field B = 5 Tesla is existing in the region. Now the conductor is rotated with a constant angular velocity $\omega =10rad/s$ about a vertical axis MN parallel to the magnetic field as shown. If the emf (in volt) induced between the points A and D of the conductor as shown is 21/n, then n is.