An electric lamp is placed behind a screen with a hole. The position of a concave mirror is adjusted until a sharp image of the hole is formed on the screen. The distance between the mirror and the screen is 40cm. determine the focal length of the mirror.

Ultraviolet radiation is dangerous because it has a high enough energy to damage skin cells. what is the best explanation of the relationship between wavelength and wave energy? a) wave energy is related only to frequency, not wavelength. b) longer wavelengths have lower frequencies but higher energy. c) the shorter the wavelength, the lower the frequency and the higher the energy. d) the shorter the wavelength, the higher the frequency and the higher the energy.