refraction Flashcards
describe what must happen for refraction to be occurring
the light passes a boundary between two transparent media. at the boundary, the light rays undergo a change in direction.
because of this the direction is being taken as?
the angle from a hypothetical lines called the normal. it is perpendicular to the surface of the boundary and is represented by single straight dotted line therefore
however what does the change in direction depend on?
the media the light ray travels between
explain when and why light would bend towards the normal
the light ray slowing down as it passes from a less optically dense material to a material that has a greater optical density. for example, when light is travelling but from air to glass.
explain when and why light would bend away from the normal
the light ray travelling as it goes from a material with a greater optical density to a material having a lower optical density
in which circumstances results in light not bending at all
whenever passing along the perpendicular normal
why does the light ray change in direction?
due to the change in speed when travelling in different substances. light passing to a denser substance means rays slow down and therefore bend towards the normal. the greater the optical density of a material, the more light is slowing down when entering it.
properties that change due to refraction
the speed and wavelength NOT frequency
technically the intensity and amplitude of the wave additionally decreases slightly upon refraction since a somewhat small portion of it reflects but this is not as noticeable as the change in speed and the wavelength therefore
define what is meant by the refractive index of a substance
the refractive index is a property of a material which measures how much light has the ability to slow down when passing through it.
can you state the letters used to represent the refractive index?
n
the equation used to calculate the refractive index?
n (refractive index) = c / cs
c = speed of light in a vaccum (ms^-1)
cs = speed of light in a substance (ms^-1)
how does the refractive index of a substance impact speed the light is travelling at?
light travels but at different speeds within different substances depending on their refractive index
a material with a higher refractive index is called optically dense, a material similar therefore causes light to slow down as it enters
the word to describe light with a high refractive index
optically dense
why is the value of n always greater than 1 therefore?
the speed of light in a substance will always be less compared to the speed of light in a vaccum.
the refractive index of air and why?
the refractive index of air can be taken to be approximately 1 it is because light whenever travelling through air doesnt slow so significantly down therefore
define Snell’s Law
it relates the angle of incidence to the angle of refraction
equation Snell’s Law
n1sinpheta1 = n2sinpheta2c
n1 = the refractive index of material 1 therefore
n2 = the refractive index of material 2 therefore
pheta1 = the angle of incidence of the ray in material 1 so
pheta2 = the angle of refraction of the ray in material 2 so
c = speed of light
how should you figure out which parts of the equation go?
pheta1 and pheta2 are always being therefore taken but instead from the normal so
Material 1 is always the material in which the ray goes through at first so .
Material 2 is always the material in which the ray goes through at second so
if the angle of incidence is increased what happens?
the angle of refraction further increases until it gets closer to about 90 degrees approximately therefore so as
describe what happens if the angle of refraction is exactly about 90 degrees to the right therefore
the light is refracted along the boundary
As the angle of incidence is increased, the angle of refraction also increases until it gets closer to about 90 degrees. however whenever the angle of refraction is exactly 90 and the light is refracted along the boundary, the angle of incidence has reached the critical angle therefore so as
at this point, the angle of incidence is known as the critical angle phetac therefore.
the equation used to calculate the critical angle?
sin phetac = n2 / n1
how can this equation be derived from Snell’s Law?
pheta1 = critical angle
pheta2 is equivalent to 90 degrees therefore so
n1 greater compared to n2
define what is meant by Total Internal Reflection
angle of incidence is greater compared to the critical angle and the incident refractive index called n1 is greater compared to the refractive index of the material at the boundary n2
the two conditions necessary for Total Internal Reflection
angle of incidence is greater than the critical therefore so angle
the refractive index therefore is n1 greater than the refractive index n2 therefore
why do diamonds sparkle loads?
diamond has high refractive index of (2.4) giving it therefore a low critical angle so light internally reflected multiple times before emerges. the diamond disperses light to colours
define optical fibres
an optical fibre is a really flexible thin tube of glass or plastic fibre that utilises the phenomenon of total internal reflection to send light signals having really high speed therefore so
the signals are sending but over large distances and in addition to round corners
the uses of optical fibres
- communications, for example for telephone and internet transmission
- medical imaging; endoscopes
explain what a stepindex optical fibre is
the optical fibre has reasonably high refractive index but are surrounded by cladding w lower refractive index to allow totals internal reflection
how do stepindex optical fibres work therefore?
Light is also shone in at one end of the fibre. Fibre so narrow meaning the light always therefore hits the boundary between the fibre and cladding at an angle bigger than the critical angle therefore. So all the light is totally internally reflected from boundary to boundary until it reaches the other end.
the so three main components making up optical fibres
- An optically dense cores for example plastic/glass therefore.
- A lower optical density cladding surrounding the core and an outer sheath.
