Optics - Refraction Flashcards
If the light travels from a “fast” medium to a “slow” medium it bends towards or away from the normal?
FST - towards
If the light travels from a “slow” medium to a “fast” medium it bends towards or away from the normal?
SFA - away
What is total internal reflection
When a wave from a slow medium to a fast medium enters at a degree larger than the incident angle, the wave can be trapped inside the slow medium
What is critical angle
When the angle of incidence results in the angle of refraction to be 90* to the normal (on the boundary line)
What are examples of refraction phenomenon?
Apparent depth: the illusion the object is closer then it appears because our brains can only trace back the reflected Rays - called the apparent depth
The mirage(flattened sun): you think you see something but it is just the displacement of light reflected off objects
Rainbows: each colour bends at a different speed and can only be seen when the sun is behind you
Examples of total internal reflection
- Right angle prisms: 90v- periscope, 180 - binoculars, bike reflectors
- Diamonds: the critical angle for a diamond is 24* and light wave trying to escape must do so at a angle less then 24* and degree higher will totally internally reflect
- Fibber optics: the light always hits the walls at an angle greater then the critical angle so it stays in the glass cylinder
Light does not reflect when it has an angle of:
0* it goes straight through
Rules for converging mirrors
1: a ray parallel to the PA will refract through PF
2: a ray through SF will refract parallel
3: a ray through the optic centre will continue unrefracted
Rules for diverging mirrors
- a ray that us parallel to the PA will refract as I’d it came from PF
2: a ray that appears to go through sf will refract parallel to the PA
3 a ray that goes through the optic centre will continue unrefracted
What is a lens?
A thin transparent piece of glass with at ,east one curved side
What can lenses do
Can make images appear:
- smaller/larger
- inverted
- upside down
- misshapen
PF(F)
Principal focal point
SF(F’)
Secondary focal point
2F
Twice the length of the focal point
F
Focal length: for the lens to the focal point
PA
Principal Axis
O
Optical centre (lens centre)
Use for converging lenses
Magnifying glass: put an object between SF and the lens to get a larger upright virtual image
Spotlight: put the beam at SF to produce a beam of parallel Rays
Projector: put object between SF and 2F the image will be larger, real and upside down. ~film must be loaded upside down
The camera: put the object beyond 2F of lens and a small inverted real image forms on the film or sensor
-farsightedness
Use for diverging lenses
Peepholes: as you look through the hole a smaller virtual image of the room are displayed in the lens
-nearsighted
Do
Distance from the object to the optical centre
Do
Distance of the image from the optical centre
Ho
Height of the object
Hi
Height of the image
F
Focal length of the lens; distance of the optical centre to the PF
