Refraction
Summary
- Refraction is the change in direction of a wave caused by a change in wave speed.
- An interface is the boundary between two different media…
- or two regions of a medium with different characteristics such as…
- density (which is often related to temperature)
- concentration of solute (salinity, for example)
- mechanical stress
- or two regions of a medium with different characteristics such as…
- In geometric optics, when an incident ray meets an interface it will be partially
- reflected
- Reflected rays obey the law of reflection described in a previous section of this book.
- Materials that reflect a significant portion of incident light appear shiny or lustrous.
- transmitted
- Transmitted rays obey Snell's law of refraction, which is described in this section of this book.
- Materials that transmit a significant portion of incident light appear clear or transparent.
- Materials that do not transmit any incident light are said to be opaque.
- absorbed
- The energy of absorbed rays is not destroyed, but changes form.
- Materials that absorb a significant portion of incident light appear dark.
- reflected
- Angles are measured with respect to the line normal to the surface.
- The angle of incidence is the angle between the incident ray and the normal.
- The angle of reflection is the angle between the reflected ray and the normal.
- The angle of refraction is the angle between the transmitted ray and the normal.
- An interface is the boundary between two different media…
- Refraction is described mathematically by Snell's law.
n1 sin θ1 = n2 sin θ2
wheren1 n2 = indexes of refraction of the two media θ1 θ2 = angles between the ray and the line normal to the surface in the two media - Snell's law describes the path of least action between two points in different media.
- The index of refraction…
- is a property of a medium
- is a measure of the "slowness" of a wave
- is defined mathematically by the formula
n = c v n = index of refraction c = speed of light in a vacuum v = speed of light in a medium - is always greater than 1 (since the speed of light in a medium is always slower than the speed of light in a vacuum)
- has no units (since it is the ratio of two speeds)
- generally increases with the density of the medium
- If a ray of light travels from…
- a medium with a low index to a medium with a high index (n1 < n2)…
- it slows down
- it refracts toward the normal
- a medium with a high index to a medium with low index (n1 > n2)…
- it speeds up
- it refracts away from the normal
- a medium with a low index to a medium with a high index (n1 < n2)…
- Total internal reflection occurs when…
- Snell's law has no real solution
- light travels from a "slow medium" to a "fast medium" (n1 > n2)
- the incident angle is greater than the critical angle
sin θc = n2 n1 - The critical angle is the incident angle that corresponds to a refracted angle of 90°; that is, the transmitted ray travels parallel to the interface.
- Dispersion
- occurs when the speed of light in a medium (and thus the index of refraction) is a function of frequency and medium
- Informally, this can be summarized as different colors travel at different speeds in some media.
- can be used to produce a spectrum
- violet refracts the most (n is "large", v is "slow" for violet light)
- red refracts the least (n is "small", v is "fast" for red light)
- is the cause of the colors seen in…
- rainbows (sunlight passing through raindrops)
- halos (sunlight passing through ice crystals)
- occurs when the speed of light in a medium (and thus the index of refraction) is a function of frequency and medium
- Birefringence