Noise with double-sided power spectral density of $\mathrm{K}$ over all frequencies is passed through a RC low pass filter with $3 \mathrm{~dB}$ cut-off frequency of $f_{c}$. The noise power at the filter output is

- $\mathrm{K}$
- $\mathrm{K} f_{c}$
- $\mathrm{K} \pi f_{c}$
- $\infty$