Chapter 23: Light, Reflection and Refraction

Lecture 12

visible light is the part of the electromagnetic spectrum with wavelength between

400 nm and 700 nm

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 

a ray is just a 

directed line that is in the direction of wave propagation 

white light is

mixture of all visible wavelengths of light 

when light strikes an object, three things can happen:

1. reflected 

2. absorbed (transformed to thermal energy)

3. transmitted 

the law of reflection states that the angle of reflection is

equal to the angle of incidence

• 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 

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

the indices of refraction on the two sides of the interface

If n2 > n1 then θ2 < θ1

• this occurs when light passes from air into water, for instance

• we say that the light bends towards the normal, since the refracted ray is closer to the normal than the incident ray is 

• also recall that the light will travel slower in medium 2 in this case 

If n2 < n1 then θ2 > θ1

• this occurs when light passes from water into air, for instance

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

• also recall that the light will travel faster in medium 2 in this case 

notice that whenever n2 < n1, the angle of refraction is

larger than the angle of incidence

• this means that the angle of refraction will reach 90 degrees before the angle of incidence does 

the angle of incidence that corresponds to an angle of refraction of 90 degrees is known as the 

critical angle, θc

for angles of incidence greater than the critical angle, θ1 > θc, there is

no refracted ray

• no light passes passes into medium 2 

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

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

wavelength increase

this means that the 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 

blue light, with its shorter wavelength, tends to diffract

more than red light

white light, which consists of a mix of all wavelengths, will be dispersed into its 

its component colors when it bends 

since violet has a shorter wavelength than red, it will 

be bent more than the red

the phenomenon of splitting of visible light into its component colors is called

dispersion