Reflection and Refraction

Reflection and Refraction

1. Reflection

   • When a wave hits a boundary between one medium and another, some of its energy is reflected. This is why you can sometimes see your reflection in puddles - light is reflected back at you.
   • The light's reflected because of the change in density - water is denser than air
   • Whenever a wave reaches a medium with a different density, some of the wave is reflected at the boundary
   • This is how ultrasound scanning works - different body tissues have different densities

2. Refraction

   • Waves travel at different speeds in substances which have different densities. Electromagnetic waves travel more slowly in denser media (usually). Sound waves travel at denser substances
   • When a wave crosses a boundary between two substances, from glass to air, it changes speed
   • If the wave hits the boundary face on, it slows down but carries on in the same direction
   • When the light shines on a glass window pane some of the light is reflected but a lot of it passes through the glass and gets refracted as it does so
   • As the light passes from the air into the glass (a denser medium), it slows down - this causes the light rate to bend towards the normal
   • When the light reaches the 'glass to air' boundary on the other side of the window, its passing into a less dense medium - so it speeds up and bends away from the normal (some of the light is also reflected at this boundary)
   • The light wave that emerges on the other side of the glass is now travelling in the same direction it was to begin with - its been refracted towards the normal and then back again by the same amount

3. A real image is where the light from an object comes together to form an image on a screen

4. A virtual image is when the rays are divering so the light from the object appears to be coming from a completely different place

5. When you look in a mirror you see a virtual image of your face - because the object (your face) appears to be behind the mirror

6. You can get a virtual image when looking at an object through a magnifying glass - the virtual image looks bigger and further away than the object actually is