A closely wound solenoid of length 50 cm and cross-sectional area 2.5 × 10-4 m2 has 200 turns. If the current in the solenoid is 4 A then find the magnitude of the magnetic field on the axis at a distance of 2 m from the center of the solenoid:
1
0.5 × 10-9 T
2
5 × 10-9 T
3
50 × 10-9 T
4
5 × 10-8 T