How many windings you have to reel up on a cylinder (length is 60cm and the diameter is 5cm) so that a Emf of 6mV gets induced if ΔI/Δt=1A/s? This is not my homework. I was doing this as a preparation. I know the formula: ε=-L*ΔI/Δt L is unknown. How to relate it to the windings, the length and the diameter of the cylinder?