A cylindrical conductor of length 6 m and cross sectional area 20 mm² has a resistance of 15 Ω. A potential difference of 120 V is maintained across the ends of the conductor. If the current density is uniform, what is its magnitude?
A. 8x 10⁵ A/m²
B. 3 x 10⁵ A/m²
C. 6x 10⁶ A/m²
D. 4x 10⁵ A/m²
E 2 x 10⁶ A/m²