Transformer p.d.s and turns obey Vp/Vs = np/ns. For an ideal 100% efficient transformer, primary and secondary powers are equal: VpIp = VsIs. Step-up transformation increases p.d. and decreases current for the same power; real transformers have losses, so state whether the ideal model is assumed. Example: An ideal transformer has primary p.d. 12 V, 100 primary turns and 100 secondary turns. Calculate secondary p.d. Vs = Vp × ns/np = 12 × 100/100 = 12 V. Use clear labels. Consider the conditions.