Physics Definitions

Accommodation relates to the ability of the eye to change its focal length and so focus on objects at a range of distances. To focus on a close object, the eye lens will be fat (having a short focal length). To focus on a far object, the lens will be pulled into a thin shape having a long focal length. Failure of accommodation gives rise to long-sightedness and short-sightedness.

The activity of a sample of radioactive material is the number of disintegrations per second taking place in that particular sample. The SI unit of activity is the becquerel (Bq).

The angle between the normal line and a ray or wave incident to a surface.

The angle between the normal line and a ray or wave reflected from a surface

The angle between the normal line and a ray or wave refracted at a surface

The critical angle is associated with refraction of light. This angle is the smallest angle of incidence at which total internal reflection (TIR) occurs.

Diffraction means the bending of wave (change in direction) and it occurs whenever a wave passes near to an obstacle. Longer wavelength waves diffract through a greater angle than shorter wavelength waves.

This is the biological risk due to exposure to radiation. The SI unit of dose equivalent is the sievert (Sv). The damage caused to cells depends on three major factors: the type of radiation, the type of tissue or cells and the total amount of energy absorbed

Gamma, X-rays, Ultraviolet, Visible, Infra-red, Microwave and Radio

The focal length of lens is measured in metres. It is the distance from the centre of the lens to the point at which rays passing through the lens meet