Chapter 23 - Light, Reflection, and Refraction

light is an electromagnetic wave that consists of

amplitudes, wavelengths, frequencies, velocities, and phases

for some applications, including reflection and refraction, we can simplify out picture and treat light

as a ray

• we don’t have to worry about oscillations, amplitudes, or phrases

• we will have to worry about wavelength/frequency in a materials that exhibit dispersion

a ray is just a

directed line that is in the direction of wave propagation

white is a 

mixture of all visible wavelengths of light 

when light strikes an object, three things can happen

• some of the light may be reflected

• some of the light may be absorbed (transformed to thermal energy)

• some of the light may be transmitted

the law of reflection states that

the angle of reflection is equal to the angle of incidence

• angles are measured from the direction normal (perpendicular) to the surface

refraction refers to 

the bending of the transmitted light at the interface between two transparent materials

reflection and refraction describe

the behavior of light at the boundary between two materials 

light at an interface - the light approaches the interface from one side, which we will refer to as medium 1

the angle the incident ray makes with respect to the normal to the surface is known as the angle of incidence, θ1

light at an interface - some of the light is reflected and remains in medium 1

the angle the reflected ray makes with respect to the normal to the surface is known as the angle of reflection, θ1

light at an interface - some of the light passes into medium 2

the angle the refracted ray makes with respect to the normal to the surface is known as the angle of refraction,θ2

the relationship between the refracted ray and the incident ray depends on1

the indices of refraction on the two sides of the interface

if wither n1 or n2 (mediums) has a dependence on wavelength, there will be a 

different angle of refraction for each wavelength 

if n2 > n1, then 

θ2 < θ1

n2 > n1 occurs when

light passes from air into water

n2 > n1 ; we say that the

light bends towards the normal, since the refracted ray is closer to the normal that the incident ray is 

light will travel slower through medium 2 if

n2 > n1

if n2 < n1, then

θ2 > θ1

n2 < n1 occurs when

light passes from water into air

if n2 < n1 - we say that

the light bends away from the normal, since refracted ray is further from the normal than the incident ray is

the light will travel faster in medium 2 if

n2 < n1

total internal reflection - notice that whenever n2 < n1, the angle of refraction is 

larger than the angle of incidence 

total internal reflection - the angle of incidence that corresponds to the angle of refraction of 90 degrees is known as the 

critical angle, θc

total internal reflection - for angles of incidence greater than the critical angle, θ1 >θc , there is no

refracted ray 

• no light passes into medium 2

• all the incidence light is reflected from the interface, a phenomenon known as total internal reflection 

A patient’s lungs can be examined by inserting a fiber-optic cable known as a

bronchoscope through the mouth (or nose) and down the bronchial tube 

the index of refraction in transparent materials such as glass decreases as

the wavelength increase

short wavelengths bend

more at a surface between two transparent materials than the long wavelengths 

amount of bending ( or diffraction) of light waves as they pass through transparent materials is

inversely proportional to the wavelength of the light

• therefore, blue light, with its shorter wavelength, tends to diffract more than red light 

thus, white light, which consists of a mix of wavelengths, will be 

dispersed into its component colors when it bends

dispersion

the phenomenon of splitting of visible light into its component colors

blue light:

shorter wavelength, larger n, more bending

red light:

longer wavelength, smaller n, less bending