Two lenses have focal lengths \[{{f}_{1}}\] and \[{{f}_{2}}\] and their dispersive powers are \[{{\omega }_{1}}\] and \[{{\omega }_{2}}\] respectively. They will together form an achromatic combination if

\[{{\omega }_{1}}+{{f}_{1}}={{\omega }_{2}}+{{f}_{2}}\]

\[{{\omega }_{1}}{{f}_{1}}={{\omega }_{2}}{{f}_{2}}\]

\[{{\omega }_{1}}{{f}_{2}}+{{\omega }_{2}}{{f}_{1}}=0\]

\[{{\omega }_{1}}-{{f}_{1}}={{\omega }_{2}}-{{f}_{2}}\]

Two lenses have focal lengths \[{{f}_{1}}\] and \[{{f}_{2}}\] and thei

1.	Two lenses have focal lengths \[{{f}_{1}}\] and \[{{f}_{2}}\] and their dispersive powers are \[{{\omega }_{1}}\] and \[{{\omega }_{2}}\] respectively. They will together form an achromatic combination if
A.	\[{{\omega }_{1}}{{f}_{1}}={{\omega }_{2}}{{f}_{2}}\]
B.	\[{{\omega }_{1}}{{f}_{2}}+{{\omega }_{2}}{{f}_{1}}=0\]
C.	\[{{\omega }_{1}}+{{f}_{1}}={{\omega }_{2}}+{{f}_{2}}\]
D.	\[{{\omega }_{1}}-{{f}_{1}}={{\omega }_{2}}-{{f}_{2}}\]
Answer» C. \[{{\omega }_{1}}+{{f}_{1}}={{\omega }_{2}}+{{f}_{2}}\]