The phase shift of the filter is ($\phi = {\phi_o - \phi_i}$):
				
				$${\phi = tan^{-1} \left({0 \over 1} \right) - tan^{-1} \left({{\omega RC} \over 1} \right)}
				
				\\= -tan^{-1} \left(\omega RC \right)$$
			
				Hence the gain and phase shift of a Passive Low-Pass filter are:
				<br>
				$|H|={1 \over {\sqrt{1+(\omega RC)^2}}}
				\\
				\phi = -tan^{-1} (\omega RC)$