A trnsformer has a primary voltage of 115 V and a secondary voltage of
24 V. If the number of turns in the primary is 345, how many turns are
in the secondary?

Hi again,

Please see this discussion and sample problem regarding primary and
secondary transformers:
http://hsc.csu.edu.au/physics/core/motors/2697/PHY934net.htm#net9

The relationship between coils and voltages is given by

V_p / V_s = n_p / n_s

where V_p = primary voltage
          V_s = secondary voltage
          n_p = primary turns
          n_s = secondary turns

Solving for n_s, we have

n_s = n_p * (V_s / V_p)

Substituting,

n_s = 345 * (24 V / 115 V) = 72

So, the secondary coil has 72 turns.


I hope this was helpful.  Please feel free to request clarification.

        -welte-ga