The square root of a negative number is, well, difficult. ... The RMS voltage of a sinusoidal is always the peak voltage divided by the square root of 2 (1.414). Yes, this means that the peak voltage of 120 volt RMS power is around 170 volts and that the peak to peak (maximum positive to maximum negative) is 340 volts.

Is RMS current always positive?

Technically, the square root of a positive number can be both positive and negative, of course, but the root operation in the RMS calculation is the PRINCIPAL square root, which is the POSITIVE root. So, your teacher is right, the RMS current is a positive value.

Why is RMS not zero?

The RMS value is the heating value or power value that has been transferred but average value is total charge that has been transferred from one terminal to other. ... Hence sinusoidal wave has non zero RMS value.