A coil of radius r = 25 cm wound of a thin copper wire of length l = 500 m rotates with an angular velocity w = 300 rad/s about its axis. The coil is connected to a ballistic galvanometer by means of sliding contacts. The total resistance of the circuit is equal to R = 21Ω. Find the specific charge of current carriers in copper if a sudden stoppage of the coil makes a charge q = l0nC flow through the galvanometer.