Most objects emit infrared energy. how do humans recognize this?

Light traveling in water, nwater = 1.33, strikes a plastic block at an angle of incidence of 51.4°; part of the beam is reflected and part is refracted. if the index of refraction of the plastic is 2.0, what is the angle made by the reflected and refracted beams?

This is the number of complete movements of a wave per second.

The voltage applied across a given parallel-plate capacitor is doubled. how is the energy stored in the capacitor affected?