Rays Flashcards
What can happen to waves (transverse or longitudinal) when they hit the boundary between 2 different materials?
Pass through the material completely unchanged (transmitted)
Pass through and change direction (refraction)
Absorbed by material
Reflected off the surface and not even enter the different material
What does a waves behaviour when it hits a boundary between materials tell us about the material?
Whether it can transmit a wave (pass through)
Absorb a wave (so it doesn’t pass through)
Reflect a wave
What does a materials interaction with waves depend on?
The material itself, what it’s made out of
The wavelength of the wave
How do light rays interact with glass mirrors?
They are reflected
So we can see our reflection
Light ray on a mirror reflection diagram description
Incident ray hits a mirror
Normal line is at right angles to the mirror
Angle between incident ray and normal line = angle of incidence
Reflected line will be at the same angle to the normal as the incident ray
Thus angle of reflection = angle of incidence
How do we use a ray diagram to show how an image will be reflected in a mirror? (Find its position)
Draw incident ray from object to mirror
Draw normal at right angles to the surface of the mirror
Draw reflected ray (at same angle)
include arrows
Draw another ray from the object + reflected ray
Extend the 2 reflected rays back into mirror, where they meet = position of reflected image
Refraction
When waves change direction from one medium to another
Because they change speed
What happens going from air —> glass for light rays?
They slow down
Thus blend towards the normal/ straighten up
When the light rays move from glass —> air?
The waves velocity increases/speeds up
And so bends away from the normal, in the same direction it was going before
What does refraction cause in an image?
For the image to shift in position
Exception to refraction
If a wave enters or leaves medium at right angles to it/ at the normal
It will not change direction
Wave front
Imaginary line that connects all the same points in a set of identical waves
Ie goes through the peaks of all waves
Refraction represented by wavefronts
The first wavefronts get closer together as they enter the new material
Showing a decrease in wavelength
So change direction towards normal
But when they leave the material they speed up
And so change direction away from normal = spread out
Wavefronts representing refraction perpendicular to the boundary
The waves will remain parallel to each other
But get closer together when they enter material/ decrease in velocity
And the whole wavefront line changes at the same time showing how they don’t change direction
Convex lenses
() shape
They focus parallel rays of light to a point called principle focus
Symbol of convex lens
Upwards arrow
⬆️
What do lens do?
Refract light
Ie change direction of rays when they move in and out
What do rays do if they pass through the centre of a lens?
Go straight through
Because it’s through the normal or principal axis
So they don’t change direction
What is the point called where all the rays of light meet together?
The principal focus aka F
Distance from centre of lens to principal focus name
Focal length
What determines the focal length amount?
The strength of the lens
When an object is at least 2 focal lengths away from convex lens diagram
One ray passes straight from the top of object through centre
Another line from top of object to the lens
This line to the lens is refracted to the focus
Where these 2 objects meet should be upside down = where the image is
When an object is at least 2 focal lengths away from lens description
The image is diminished
The image is inverted
The image is real because the rays actually meet at a point
When an object is between 2 focal lengths and one focal length from convex lens
Same as if it were 2
Line straight from top of image through centre
Line parallel to principle axis to the lens
This ray is refracted through the focus
Where these 2 rays meet = image
