Refraction

• Explain what happens to light when it enters a glass block from air

  Glass is denser than air, so when light passes from air into glass it slows down. If the ray meets the boundary at an angle to the normal, it bends towards the normal.
• Explain what happens to sound when it enters a glass block from air

  When sound changes mediums (enters a different material) at an angle other that 90 degrees, it is bent from its original direction. 
• What is a medium?

  A medium is a material or method used for communication or artistic expression.
• Explain why when white light is passed through a glass block, it can be separated into the colours of the rainbow

  Because each color is refracted differently, each bends at a different angle, resulting in a fanning out and separation of white light into the colors of the spectrum.
• Why is grass green?

  During photosynthesis, chlorophyll absorbs energy from blue- and red-light waves, and reflects green-light waves, making the plant appear green.
• Why is the sky blue?

  The sky appears blue because of a phenomenon called Rayleigh scattering. When sunlight enters Earth's atmosphere, it is scattered by molecules and tiny particles in the air. Shorter wavelengths of light, such as blue and violet, are scattered more than longer wavelengths like red and orange. This scattering of shorter wavelengths is what makes the sky appear blue to our eyes.
• Why is water colourless and transparent?

  That is, the molecules of water cannot absorb visible light and so cannot yield colors like dye or pigment molecules. 
• Why is most of our paper white and opaque?

  Lignin is a natural compound found in wood fibers that gives them a yellowish-brown color. By eliminating lignin, the paper appears brighter and whiter. Brightness and Opacity: The bleaching process also enhances the brightness and opacity of the paper.