The electric motor in a toy train requires a voltage of 4.9 v. find the ratio of turns on the primary coil to turns on the secondary coil in a transformer that will step the 110 v household voltage down to 4.9 v.

So to solve for this problem, this is computed by the following steps:

Vp / Vs ( = Np / Ns

Where:

Vp = Voltage Primary

Vs = Voltage Secondary

Np = Turn ratio Primary

Ns = Turn ratio Secondary.

So plugging in our values:

110 / 4.9 = N p / Ns

N p / Ns = 22.44, so the answer is 22 coils.