a.
The magnetic field due to solenoid is,
          B =
uonI
Differentiate the above equation on both sides,
         dB/dt =
uon dI/dt
The expression for the electric field inside the solenoid
is,
      E = r/2 dB/dt
          =
(r/2)uon dI/dt
          =
(0.550x10-2 m /2)(4(pi)x10-7 T.m/A)(870)(65.0
A/s)
          =
1.95x10-4 N/C
-----------------------------------------------------------------------------------
b.
The expression for the electric field inside the solenoid
is,
      E = r/2 dB/dt
          =
(r/2)uon dI/dt
          =
(1.00x10-2 m /2)(4(pi)x10-7 T.m/A)(870)(65.0
A/s)
          =
3.55x10-4 N/C
