Answer:
(a) B = 2.85 ×
Tesla
(b) I = I = 0.285 A
Step-by-step explanation:
a. The strength of magnetic field, B, in a solenoid is determined by;
r =

⇒ B =

Where: r is the radius, m is the mass of the electron, v is its velocity, q is the charge on the electron and B is the magnetic field
B =

=

B = 2.85 ×
Tesla
b. Given that; N/L = 25 turns per centimetre, then the current, I, can be determined by;
B = μ I N/L
⇒ I = B ÷ μN/L
where B is the magnetic field, μ is the permeability of free space = 4.0 ×
Tm/A, N/L is the number of turns per length.
I = B ÷ μN/L
=

I = 0.285 A