"true or false. in a phase contrast microscope, the phase plate causes undiffracted light waves to undergo a phase shift by 1/2 wavelength."

False

In a phase contrast microscope, the phase plate causes diffracted light waves to undergo a phase shift by 1/2 wavelength.

Explanation:

Phase contrast microscope is dependent on the difference in refracting index from object to surrounding. Light beam passes through the organism and it gets refracted through it. The phase change is difference in the refracting index of the two medium through which light passes.

Thus, the diffracted beam of light causes the phase shift by 1/2 wavelength.