A transformer has 500 turns of the primary winding and 10 turns of the secondary winding. Determine the secondary voltage if the secondary circuit is open and the primary voltage is 120 V.

First we use the fact that the ratio of the voltage on the secondary and on the primary will be the same as the ratio of the number of turns of both coils,

$\Rightarrow u=\frac{u_2}{u_1}=\frac{N_2}{N_1}$

We evaluate the unkown secondary voltage -

$\Rightarrow u_2=\frac{N_2}{N_1}{u}_1$

We substitute the given values -

$\Rightarrow u_2=\frac{10}{500}\times 120v=2.4v$

Hence, the answer is $2.4v.$