When electromagnetic waves meet a substance, the substance may absorb, transmit, refract or reflect them. What happens depends on the wavelength. Glass transmits visible light but absorbs most ultraviolet, and a metal sheet reflects microwaves.
Refraction happens when a wave crosses a boundary between two different media and changes direction. It is caused by the wave changing speed. When light slows down on entering glass from air, the ray bends towards the normal. When it speeds up on leaving the glass, it bends away from the normal. A ray travelling along the normal is not bent. On a wave front diagram (Higher tier), the wave fronts get closer together as the wave slows down, because the frequency stays the same while the wavelength gets shorter.
Required practical 10 investigates how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface. One method uses a Leslie cube, a hollow metal cube with four different side surfaces such as matt black, shiny black, matt white and shiny silver. Fill it with hot water. Hold an infrared detector the same distance from each side in turn and record the reading. Keep the distance and the water temperature the same, so that only the type of surface changes. Matt black gives the largest reading, so it is the best emitter. Shiny silver gives the smallest reading. Matt black surfaces are also the best absorbers of infrared.