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Light of wavelength $\mathrm{\lambda }$ strikes a photo-sensitive surface and electrons are ejected with kinetic energy E. If the kinetic energy is to be increased to 2E, the wavelength must be changed to $\mathrm{\lambda }\text{'}$where
(a) $\mathrm{\lambda }\text{'}=\frac{\mathrm{\lambda }}{2}$            (b) $\mathrm{\lambda }\text{'}=2\mathrm{\lambda }$
(c) $\frac{\mathrm{\lambda }}{2}<\mathrm{\lambda }\text{'}<\mathrm{\lambda }$       (d) $\mathrm{\lambda }\text{'}>\mathrm{\lambda }$