Question

The RMS value of the voltage u(t) = 3 + 4cos(3t) is

• A. $\sqrt{17}$ V
• B. 5 V
• C. 7 V
• D. $(3+2\sqrt{2})$ V

Answer 1

The correct option is A $\sqrt{17}$ V

RMS value of d.c voltage = $V_{dc}$ (rms)= 3V

RMS value of a.c voltage = $V_{ac}$ (rms)= $\frac{4}{\sqrt{2}}$V

$\therefore$ RMS value of the voltage
$=\sqrt{3^2+{\left(\frac{4}{\sqrt{2}}\right)}^2}=\sqrt{9+8}=\sqrt{17}$ V