In a step-up transformer, the relationship between voltages on the primary and secondary coil and the number of turns in the two coils is
[tex] \frac{V_p}{V_s} = \frac{N_p}{N_s} [/tex]
where V means voltage, N is the number of turns, and p and s refer to the primary and secondary coil, respecitvely.
In our example, we have Vp=80 V and Vs=160 V, and the primary coils have Np=40 turns, so we can find the number of turns in the secondary coil, Ns:
[tex]N_s=N_p \frac{V_s}{V_p}=(40) \frac{160 V}{80 V}=80 [/tex] turns
