Transcript LIGHT
LIGHT A FORM OF ELECTROMAGNETIC RADIATION THAT STIMULATES THE EYE I. Electromagnetic Radiation A. Light is a wave and therefore has all the properties of waves. B. Light waves have wavelengths that range from 380nm to 760 nm C. Studying light allows us to study all electromagnetic radiation D. White light is all colors mixed together E. Monochromatic light is light of one color, a single wavelength or frequency The numbers listed here are frequencies not wavelengths to find the wavelengths Remember v=fλ II. Movement of light A. Light travels in a straight line B. The speed of light is constant in a given medium (like the speed of all waves within a medium) C. Light travels fastest in a vacuum (space) D. Denoted by the symbol c, found on the table of constants on reference tables c= 3 X 108 m/s This refers to all forms of electromagnetic radiation not just visible light. E. Electromagnetic Radiation is produced by the movement of charged particles F. In a material medium the speed of light is always less than in a vacuum. 1. it varies with a. Optical density of the medium b. Frequency G. The speed of light in air is very close to the speed of light in a vacuum, The same value is generally used for both III. REFLECTION A. Law of Reflection 1. Statement: When a light ray is incident upon a reflecting surface the angle of incidence is equal to the angle of reflection. θi = angle of incidence θr angle of reflection Normal is a line perpendicular to the reflecting surface B. Regular Reflection 1. Occurs when light hits a polished surface (flat). This is when the law of reflection applies 2. The reflected rays are all parallel because normals are parallel C. Diffuse reflection 1. occurs when light hits an irregular surface. 2. The reflected rays are scattered. Not parallel because the normals are not parallel IV. REFRACTION A. The bending (change in direction) of light as it moves from one medium to another. B. The incident ray strikes the boundary between two media. It will change direction and speed as it enters the new medium. C. When the angle of incidence is zero, along the normal, the ray passes straight through into the θ1 is the angle the incident ray makes with the normal (line perpendicular to surface) θ2 is the angle the refracted ray makes with the normal F. D. Optical Density- property of a medium that determines the speed of light 1. the more dense the slower the light will travel and vice versa E. The refracted ray will bend toward the normal when it enters a more optically dense medium. The refracted ray will bend away from the normal when it enters a medium that is less optically dense. Example of light entering a more dense medium. The ray bend toward the normal and slows down Example of a light ray entering a less dense medium and bends away from the normal and speeds up G. Absolute Index of Refraction 1. More optically dense media have a higher index of refraction. 2. Values are 1.00 or greater 3. represented by n 4. n=c/v n = absolute index of refraction c= speed of light in a vacuum, 3.0X108m/s v= speed of light in a given medium, m/s 5. Values on Reference Tables H. Snell’s Law 1. Gives the relationship between angle of incidence and angles of refraction to the index of refraction 2. n1sinθ1 = n2sinθ2 n1= index of refraction of incident medium n2 = index of refraction of refracted medium θ1= the angle of incidence θ2 = the angle of refraction I. The relationship between index of refraction, velocity and wavelength is given by: n2 = v1 = λ1 n1 v2 λ2 Where 1 represent medium 1 and 2 represents medium 2 Units v= velocity m/s λ = wavelength,m n2/n1 is called the relative index of refraction. J. Critical angle 1. Definition- the measure of the incident angle that causes the refracted ray to lie right along the boundary between the two mediums. 2. unique to a substance. 3. To calculate, use Snell’s law and substitute in 90 for the refracted ray. n1sin θ1 = n2sin 90 AS θ1 INCREASES SO DOES θ2, UNTIL IT IS EQUAL TO 90. THEN THE REFRACTED RAY MOVES ALONG THE BOUNDARY OF THE 2 MEDIUMS K. Total internal reflection 1. occurs when the critical angle is exceeded, light can no longer escape and is reflected back into the medium. 2. Law of reflection applies here V. Dispersion A. As light enters a medium each wave of different frequency (color) travels at different speeds. B. When white light falls on a prism, the waves of each frequency refract by different amounts, separating the colors. C. Red light refracts the least because red light has the highest velocity in glass. Violet the most. VI. Polarziation of Light A. Def: Separation of a beam of light so that the vibrations are in one plane. B. Property of transverse waves. C. Light can be polarized so it must be a transverse wave. Doppler and light When an object emitting light (like a star) is moving away from another object (like the earth) the wavelength of light appears to be getting longer which means that the color of the light is shifted toward the red end of the spectrum. This is what is meant by red shift. Conversely if an object is moving toward another then the shift is toward the blue end of the spectrum.