An electron of mass $m$ and a photon have same energy $E$. The ratio of wavelength of electron to that of photon is: ($c$ being the velocity of light)\\
(1) $\frac { 1 } { c } \left( \frac { 2 m } { E } \right) ^ { \frac { 1 } { 2 } }$\\
(2) $\frac { 1 } { c } \left( \frac { E } { 2 m } \right) ^ { \frac { 1 } { 2 } }$\\
(3) $\left( \frac { E } { 2 m } \right) ^ { \frac { 1 } { 2 } }$\\
(4) $c ( 2 m E ) ^ { \frac { 1 } { 2 } }$