A solenoid of 1 . 5 metre length and 4 .0 cm diameter possesses 10 turns per cm. A current of 5 ampere is flowing through it. The magnetic field at axis inside the solenoid is (Given:${\mathrm{\mu }}_0=4\mathrm{\pi }\times {10}^{-7}$ weber/amp metre)

• A

  $2\mathrm{\pi }\times {10}^{-3} \mathrm{tesla}$

• B

  $2\mathrm{\pi }\times {10}^{-5} \mathrm{tesla}$

• C

  $4\mathrm{\pi }\times {10}^{-3} \mathrm{gauss}$

• D

  $2\mathrm{\pi }\times {10}^{-5} \mathrm{gauss}$