What is:
Refractive index
(Real definition and IGCSE)
- A ratio for speed between two mediums
- In GCSE this is speed of light in a vacuum/speed of light in the medium
- This does not have a unit
What is:
Snell’s law
N = sin(i)/sin(r)
N1 sin (feta1)=N2sin(feta2)
GCSE makes N1 always air or a vacuum, so n1 would always be 1
What are:
Angles of incidence and refraction
- angle of incidence is angle from the incoming ray to the normal
- angle of refraction is angle from the refracted ray to the normal
What is:
Refraction
(stock answer)
Waves change speed and direction as they travel from one medium to another
Why does:
Refraction occur
Refraction happens as the wave changes direction as it passes from one medium to another as one side of the wave gets slowed/sped up first which changes the direction of the wave
How would you go about:
Measuring refractive index
Measure values of incidence and refraction using a protractor form lines drawn with a ruler and pencil from a laser on a transparent medium. Repeat each angle to calculate a mean to reduce random error, and plot sin i vs sin r to find the gradient and therefore refractive index.
What are:
Transverse and longitudinal waves
Transverse waves - waves that oscillate perpindicular to the direction of energy transfer
Longitudinal waves - waves that oscillate parallel to the direction of energy transfer
How to draw:
Wave diagrams
- draw ray diagram
- draw waves of equidistance of same distance apart until they enter new medium
- Draw waves perpindicular to the ray
- When waves change medium, the distance between waves contract/expand depending on the speed change
How to draw:
ray diagrams
- draw medium
- draw normal perpindicular to medium
- draw direction of ray at correct angles and label them with arrows
- Label the size of angle of incidence and refraction
What is formula for:
Critical angle
C = sin^-1(n1/n2)
In GCSE, n1 = 1
What is the:
Critical angle
The angle of incidence passing through a medium where the angle of refraction in another medium is 90 degrees
what is:
TIR
Total Internal Reflection is when 100% of a wave is reflected becuase the angle of incidence is > the critical angle
What are the conditions for:
TIR
- The medium light is entering has a lower refractive index
- Angle of incidence>critical angle
What are:
Examples and uses of TIR
High visibility prisms, e.g. in a bike, where critical angle is less than 45 degrees such that light is reflected back
Fibre optic cables, which are designed in a ≈≈≈ format such that the data from the light does not escape as it is endlessly refracted in the fibre optic cable.
