p5.2- optics- defraction, refraction, TIR, lenses, image formation, polarisation Flashcards
What is refraction?
When the waves are approaching the interphase between two medias at an angle the change in speed causes a change indirection as well.
Why does refraction happen?
When the waves pass from one medium to another, there is a change in speed.
The frequency remains constant, so there is a change in wavelengths.
What is the refractive index?
A measure of the amount pf refraction caused by different materials.
It is equal to the ratio of light in a vacuum to the speed of light in a material.
n=c/v
c= speed of light in air
v=speed of light in medium
What does Snell’s law show?
The relationship between direction and refractive index
What is Snell’s law?
n1 sin θ1 = n2 sin θ2
n1= refractive index of material light is travelling from
n2=refractive index of which light is travelling into
θ1=measured angle of incidence
θ2= measured angle of refraction
What is airs refractive index?
1- the other material will always be compared to air.
What is dispersion?
It is the spreading of white light into its full spectrum of wavelengths
What are the equations for dispersion if the ray enters the prism from air?
sin θ1=c ×sin θ2/fλ
sin θ2=fλ×sin θ2/c
Why does the smallest wavelengths bend the most towards the normal?
As frequency stays constant throughout refraction, and the speed of light in a vacuum must be constant, if we keep the same angle of incident then the sine of the angle of refraction will be proportionate to the wavelength.
-violet( smallest wavelength)= bend most
-red( largest wavelength)=bend least
Why does wite light disperse when it passes throughs prism ?
-Because the light will change speed and travel more slowly in a dense medium.
-As light bends it splits and bends towards the normal.
- The single beam separates into different colours because they have different wavelength and therefore bends at different angles towards the medium
- Dispersion
What are the conditions for total internal refraction?
- Light must be travelling from a more dense medium to a less dense medium.
-The angle of incidence must be grater than the critical angle
What is the equation for working out The refractive index of the more dense material from its critical angle?
n=1/sin θ
What is the method for working out a materials refractive index from its critical angle?
- Use a semi- circle block of your material and use a lamp with a slit, to shine a singular ray through the box.
-Adjust the lamp until the refracted ray is directly on top of the barrier
-Measure the angle of incidence ray and work out the refractive index of material using
-n=1/sin θ - Repeat with different angle to try and find the most accurate critical angle.
What does a concave/diverging lens look like?
It caves inward and spread the light rays out.
What does a convex/ converging lens look like?
It curves outwards and directs the rays inwards towards a point.
What is the equation for power of a lens?
Power=1/focal length
How do you add lens powers?
You add convex power and minus concave power.
What is diffraction?
The spreading of wave energy through a gap or around an object and the waver energy spreads into the space behind the gap.
what does the amount of diffraction depend on?
The wavelength
How does the size of the gap effect the diffraction?
-If the wavelength as the same size as the gap you get maximum diffraction.
-if the gap is too small then no energy can pass through and that is why there may not be diffraction.
- of the gap is too large there will be little effect as the wave will pass through undisturbed.
what happens at constructive interference when light passes through a diffraction grating?
- Bright maxima’s are formed.
what happens at destructive interference when light passes through a diffraction grating?
Dark minima spots are formed.
How does the dark bands correlate and the distance between the slits?
Space between dark bands=1/distance between two slits.
What is the diffraction grating equation?
nλ=dsinθ
What is the equation for intensity?
Intensity Power/Area
What is the critical angle ?
The angle of incidence which the angle reflects at 90 degrees.
What is the equation used to calculate the critical angle?
SinC= 1/n
What does electron diffraction provide evidence for ?
The wavelike nature of electrons. It suggests that particles can demonstrate wavelike properties.
If electrons didn’t have a wavelike nature, describe the effect you would see when they’re passed through a slit.
A single bright region would be formed
What is total internal reflection?
Its where all the light is reflected back at the boundary between two mediums.
It occurs when light is travelling from a more dense medium to a less dense medium and the incident angle is greater than the critical angle.
What is the focal length of a lens?
The distance between the centre of the lens and the focal point
What is the real image ?
One that can be projected onto a screen and is always inverted.
They a\re consequences of light meeting at there focal point.
What is a virtual image?
Formed on the same side of the lens of the objected and cannot be projected onto a screen.
How do you work out the magnification of an object?
image height/ object height
What is plane polarisation?
When the oscillation of light in restricted to one plane.
