Refraction of Light

Refraction  The bending of light as it travels, at an angle, from a material with one refractive index to a material with a different refractive index.  Light travels at a constant speed and a straight line as long as it is in the same medium  The bending of light as it travels, at an angle, from a material with one refractive index to a material with a different refractive index.  Light travels at a constant speed and a straight line as long as it is in the same medium

Fermat’s Principle  Light will choose the path that takes less time to travel through

Using Rays to Describe Refraction  Reflected ray and incident ray are the same.  Refracted ray: the ray that is bent upon entering a second medium.  Angle of refraction: the angle between the normal and a refracted ray (represented by upper-case R)  Reflected ray and incident ray are the same.  Refracted ray: the ray that is bent upon entering a second medium.  Angle of refraction: the angle between the normal and a refracted ray (represented by upper-case R)

Direction of Refracted Ray  When a light ray travels from a medium where the speed is faster (air) to a medium where it’s slower (water), the refracted ray bends toward the normal.  When a light ray travels from a slow medium to a fast medium, the refracted ray bends away from the normal.  When a light ray travels from a medium where the speed is faster (air) to a medium where it’s slower (water), the refracted ray bends toward the normal.  When a light ray travels from a slow medium to a fast medium, the refracted ray bends away from the normal.

Index of Refraction  Is the ratio of the speed of light in a vacuum to the speed of light in a given medium.  n = c v  n is the index of refraction  c is the speed of light in a vacuum  v is the speed of light in a medium  Is the ratio of the speed of light in a vacuum to the speed of light in a given medium.  n = c v  n is the index of refraction  c is the speed of light in a vacuum  v is the speed of light in a medium

Dispersion  The process of separating colours by refraction.  White light includes all the wavelengths of visible light.  When you shine white light through a prism, the light is separated due to each colour having a different wavelength and therefore move at different speeds.  The process of separating colours by refraction.  White light includes all the wavelengths of visible light.  When you shine white light through a prism, the light is separated due to each colour having a different wavelength and therefore move at different speeds.

Problems…  Calculate the speed of light in fused quartz.  Step 1: look up the index of refraction for fused quartz in Table 11.1 on page 454. (standardized values)  Step 2: write the equation n= c/v  Step 3: substitute and solve 1.46 = 3.00 x 10 8 m/s v 1.46v = 3.00 x 10 8 m/s v = 2.05 x 10 8 m/s  Calculate the speed of light in fused quartz.  Step 1: look up the index of refraction for fused quartz in Table 11.1 on page 454. (standardized values)  Step 2: write the equation n= c/v  Step 3: substitute and solve 1.46 = 3.00 x 10 8 m/s v 1.46v = 3.00 x 10 8 m/s v = 2.05 x 10 8 m/s

You Try It!  P. 455 # 1-4  P. 456 # 1-3, 5, 8.  P. 455 # 1-4  P. 456 # 1-3, 5, 8.