1. The problem statement, all variables and given/known data A long solenoid of radius R, length L (which is much longer than R), number of windings N, has a current I that is changing in time at a rate (dI/dt). What is the magnitude of the electric eld a distance R=2 from the axis of the solenoid? 2. Relevant equations μ0(N/L)I 3. The attempt at a solution I thought I had this completely right until I get to the R/2 Part. if you just throw the R/2 part into the equation, then you get the B field I believe, but the answer is: μ0(dI/dt)(N/L)R/4. I am not seeing where the 4 in the denominator comes from unless we had some kind of divisible action of R going on somewhere, or something. Not really sure how to proceed!