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Lecture 10

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PHGY 1030
Luming Wang

. PROPERTIES OF LIGHT Light Electromagnetic radiation:  Wavelength: the distance between successive peaks or troughs  Frequency: the number of waves per second  Amplitude: the difference between wave trough and peak The energy content of electromagnetic radiation is proportional to its frequency [i.e. high frequency (short wavelengths) has the highest energy content].  Only a small part of the electromagnetic spectrum is detectable by our visual system. This visible light consists of wavelengths of 400-700 nm. (see Fig. 9.2)  “Hot” colours (e.g. red or orange) have long wavelength light and less energy than “cool” colours (e.g. blue or violet). Optics In a vacuum, a wave of electromagnetic radiation will travel in a straight line. This is a ray.  Reflection: the bouncing of light rays off a surface. This depends on the angle at which it strikes the surface. A ray striking a mirror perpendicularly is reflected 180˚ back upon itself and a ray striking a mirror at 45˚ angle is reflected 90˚.  Absorption: the transfer of light energy to a particle or surface. Black surfaces absorb the energy of all visible wavelengths. Some absorb light energy only in a limited range of wavelengths and reflect the remaining wavelengths. For example, a blue pigment absorbs long wavelengths but reflects a range of short wavelengths centered on 430 nm that are perceived as blue.  Refraction: the bending of light rays that occur when they travel from one transparent medium to another. It occurs because the speed of light differs in two media (e.g. light passes through air more rapidly than through water). The greater the difference between the speeds of lights in the two media, the greater the angle of refraction. (see Fig. 9.3). THE STRUCTURE OF THE EYE Gross Anatomy of the Eye  Pupil: the opening that allows light to enter the eye and reach the retina. It appears dark due to the light-absorbing pigments in the retina. 
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