To get three images of a single object, the angle between the two plane mirrors should be

A parallel beam of monochromatic light falls normally on a single narrow slit. The angular width of the central maximum in the resulting diffraction pattern

For the diagram shown, the resistances between points A and B when ideal diode D is forward biased is '$$R_1$$' and that when reverse biased is '$$R_2$$'. The ratio $$R_1: R_2$$ is

The maximum kinetic energy of the photoelectrons varies