How do I determine the rate of flux change in circuit in which 15 V is induced in a 30-turn coil?

Question

How do I determine the rate of flux change in a circuit in which 15 volts is induced in a 30-turn coil?

Answer 1

Hi Leonard:

 

It looks you would want to use Faraday's law, which (as you may know) relates the induced emf, or voltage, in a coil to the time rate of change of magnetic flux through the coil, as:

 

ε = -N(ΔΦ_B/Δt)  

 

where 

 

ε = induced electromotive force (emf), aka induced voltage

N = number of loops (or turns, in a coil)

(ΔΦ_B/Δt) = time rate of change of magnetic flux (Φ_B)

 

The negative sign out front on the right relates to which way any induced current will flow, and so does not concern us here, as we are only interested in magnitudes, not directions.

 

Often, with this law, we are given N, and information that allows us to calculate (ΔΦ_B/Δt), and are then asked to compute the induced voltage (emf) ε.  But in this case, you are given N and ε, and asked to compute the time rate of flux change (ΔΦ_B/Δt).  So treat (ΔΦ_B/Δt) as the "unknown" in Faraday's law, and solve for it, given the other information.  The result should be in base units for time rate of flux change, webers per second (Wb/s) or tesla-meters squared per second (T·m²)/s.

 

Let me know if you would like to check a result, or if you have any other questions!