All of these substances are<em> </em>alloys (a substance made from melting two or more substances, one of them usually being a metal). Brass is a combination of copper and zinc, bronze is mostly copper, tin and other non-metals as well and steel is majorly made up of iron and copper. These alloys have various uses and varying importance in different kinds of industries.
The amplitude of a wave is the distance between a point on one wave and the identical point on the next wave. The period and wavelength of a wave are inversely proportional.