Topic 5

• The angle of incidence behind which a wave will undergo total internal reflection.

  Critical Angle
• Bodies at a fixed temperature radiate the same average power that they absorb.

  Constant Temperature
• A lens that is thicker at the edges than in the centre. Parallel rays diverge when passing through.

  Concave Lens
• A lens that is thicker in the centre than at the edge. Parallel rays converge when passing through.

  Convex Lens
• The reflection of a wave from a rough surface that results in the wave being scattered.

  Diffuse Reflection
• Transverse waves that transfer energy from the source of the waves, to an absorbed. They form a continuous spectrum of different frequencies and all travel at the same speed in a vacuum.

  Electromagnetic Waves
• The distance between the centre of a lens and its principal focus.

  Focal Length
• High energy radiation rays used for detecting and treating cancers, and sterilsing food and medical implements. They can cause cell damage and mutations.

  Gamma Rays
• Used for cooking food, thermal imaging and short range communications. It can cause skin burns.

  Infrared
• An object that forms an image through the refraction of light.

  Lens
• Used for satellite communications and for cooking food. They can cause internal heating of body cells.

  Microwaves
• Equal to the reciprocal of the focal length of a lens. Concave lenses have negative powers whereas convex lenses have positive powers.

  Power of Lens
• The point before or after a lens where light rays appear to meet. The rays may converge or diverge away from this point.

  Principal Focus
• Used for television and radio signals. They can be produced by oscillations in electrical circuits, or can induce these oscillations themselves.

  Radio Waves
• A visual representation of the path of a wave, usually around the point where it meets a boundary. Rays are usually drawn as straight limes with an arrow pointing in their direction of travel.

  Ray Diagram
• An image produced by light-rays physically converging. Real images are ones that can be projected onto a screen.

  Real Image
• The reflection of a wave from a smooth surface.

  Specular Reflection
• A process that occurs when a wave meets the boundary from a medium with a high refractive index to one with a lowe refractive index, at an angle of incidence greater than the critical angle. All the wave is reflected at the boundary.

  Total Internal Reflection
• Used in energy efficient lamps, disinfecting water and for sun tanning. It can cause cell and eye damage that can result in skin cancer and eye conditions.

  Ultraviolet
• An image produced by the apparent, but not actual divergence of light-rays. Virtual images cannot be projected onto a screen.

  Virtual image
• The only type of electromagnetic radiation that our eyes can detect. It is used for fibre optic communication and photography.

  Visible Light
• Used for medical imaging and security scanners. They can cause cell damage and mutations.

  X-rays