Lecture 2 - Refraction Flashcards
What is refraction
when a wave or light ray moves from one medium to another e.g. air/glass/water causing speed and direction to change
What does refraction cause
Bending of light - wavefront tilted
= changes direction
What happens when light travels from a fast medium to a slow medium
e.g. air to glass/water
Refractive index of glass HIGHER than air
SLOWS down, ray of light TOWARDS normal
Angle of refraction < angle of incidence
What happens when light travels from a slow medium to a fast medium
e.g. glass/water to air
SPEEDS UP
ray of light AWAY from normal
Angle of refraction > angle of incidence
Whats the rule for rays and wavefronts
Rays and wavefronts are 90 degrees/ perpendicular to each other
How do ripples work
Stone in pond
Starts circular and steep
Less steep as wavefronts move away
Eventually flat and parralel lines, less circular large distance away
Where do ripples of water travel
Outwards
Away from where rock fell in water
What is the refractive index formula
n = c/v c = speed of light in vaccum v = speed of light in medium
is n negative or positive number
positive
what is snells law formula
n sin i = n' sin i' n = refractive index before refraction i = angle of incidence n' = refractive index after refraction i' = angle of refraction
what is prism
correct squint - moves object so it goes onto fovea
How to correct squints
- Object moved towards angle of prism
- Control how much it moves by how big angle is
- Also swap direction - rotate it
Dispersion in rainbow
different wavelengths dispersed = rainbow = different colours
shine white light
Does it travel faster or slower in middle of lens and why
slower
because thicker
what part of wavefront hits lens first
middle before edges
where do spherical wavefronts converge to
focal point
what does a shorter focal length show
F closer to lens but power of lens increases
Equation for working out power
F = 1/f F = surface power f = focal point
what is object distance ( I )
Distance of object FROM lens axis
what is image distance ( I’ )
Distance of image from lens axis
what is focal length (f )
Distance of focal point from lens axis
what is surface power ( F )
power of lens
what is focal point ( F’ )
point on optical axis where rays meet
Is distance form surface(lens) to object negative or positive
negative
Is distance from surface ( lens ) to image negative or positive
positive
what does the lens equation show
equation for distance between lens, image and distance
what is lens equation
1/l' = 1/l + 1/f l' = image distance l = object distance f = focal length
formula for magnification
l’/l
size of image/size of object
does light move slower in air or glass
glass
what is index of refraction for light in a vaccum
1
