The steady value of emf which produces the same amount of heat in a resistance in a given time as the alternating emf does in the same resistance in the same time is called the
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → rms emf
The heat produced in a resistor depends on the average power loss. For an alternating emf, this average is the same as that of a steady emf equal to its root mean square (rms) value, \( V=v_m/\sqrt{2} \). So the rms value is also called the effective value.
NCERT (2026-27):
AC Voltage Applied to a Resistor – “… In fact, the I or rms current is the equivalent dc current that would produce the same average power loss as the alternating current.”
AC Voltage Applied to a Resistor – “Similarly, we define the rms voltage or effective voltage by
\( \displaystyle V=\frac{v_m}{\sqrt{2}}=0.707\,v_m \qquad (7.8) \)”