Question

the effective value of an ac voltage is the electrical energy that has the same effect as a dc voltage of the same value.
a lab scope will display the peak values of the ac voltage sine wave, but a multimeter measures the effective value of that same ac voltage.
the effective value of an ac voltage is 70.7% of the peak value. the effective value is calculated by multiplying the peak value by 0.707. this is also called the root mean square or rms voltage of a sinusoidal waveform.
if you measure the voltage across l2 with a multimeter, you will measure...
12 v.
17 v.
the effective value.
the peak value.

Explanation:

A multimeter measures the effective (RMS) value of AC voltage. For a standard 12V RMS AC supply, the peak value is ~17V, but multimeters read the effective value.

Answer:

12 V.
the effective value.