Number of turns per unit length of solenoid, n=70 turns ∕cm=7000 turns ∕m ∴ Magnetic field inside the solenoid due to current I, B=µ0nI⋅⋅⋅⋅⋅⋅⋅(i) Since, electron is moving inside the solenoid in circular path of radius r , then r=
mv
Be
⇒r=
mv
µ0nIe
[From Eq. (i)] ⇒I=
mv
µ0nre
Here, m=9.1×10−31kg,v=4.4×106m∕s. e=1.6×10−19C⇒µ0=4π×10−7 SI unit r=2.5cm=2.5×10−2m - Putting these values in the above equation, we get I=