Question

effective voltage
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.

1
in the picture you see two lamps. the left lamp is connected to a dc voltage of 12 v. the right lamp is connected to an ac voltage.
read the voltage used to power the two lamps.

the peak value for the ac waveform is 12 volts.
the effective value of the ac waveform is 12 v.
the waveform on channel a is 12 volts dc.

Explanation:

The problem states the DC voltage is 12 V, and the AC voltage has the same effective (RMS) value as the DC voltage to have the same effect on the lamp. The effective value of the AC voltage matches the DC voltage of 12 V, so this option is correct. The peak value would be $\frac{12}{0.707} \approx 16.97$ V, so the peak value option is wrong. Channel A is the DC supply, so the third option is incorrect as it is marked wrong in the image.

Answer:

The effective value of the AC waveform is 12 V.