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
When an object is between 2 focal lengths and one focal length from convex lens description
Inverted
Enlarged
Real
So, what is the difference in outcome between position of object using convex lens
More than 2 focal lengths from lens =
DIMINISHED
Inverted
Real
BUT object is between 1 and 2 focal lengths =
MAGNIFIED
inverted
Real
What represents a magnifying glass?
Putting an object less than 1F away from the convex lens
Ray diagram of object less than 1F away/ magnifying glass
Draw line straight through centre
Draw line from top of object parallel to the principle axis to the lens
This line then refracts through focus
These rays do not meet therefore we draw dotted lines to extend them behind the lens
They will meet = position of image
Properties of image produced when magnifying glass/ object is 1F away from lens
Enlarged/magnified
Upright
Virtual as they are not made by real rays that meet at a point
When do convex lens produce virtual images?
Only if it’s a magnifying glass
Aka less than 1F away
What does it mean if an image is virtual?
It’s not real as the lens only appear to meet at a point
So it would not show up on a screen
How to find magnification?
Image height / object height
Concave lens
)( look like this
Make rays of light diverge ie spread out
Symbol for concave lens
⬇️
⬆️
Principle focus for concave lenses
If you continue the lines of the diverted rays
They join at a specific point = principal focus
Do concave lens focus light at principle focus?
No they don’t actually because real rays do not join up there
They only appear to
Ray diagram for concave lens
Ray line going straight through centre
Line parallel to principle axis hits the lens
Dotted line from focus to the line above
But hard line extended from it after passing through lens
Where they meet = image
Concave lens image produced description
Upright
Diminished
Virtual
Speculation reflection
When light reflects in a singular direction that is perpendicular to each other
Always on smooth surface aka mirror
Produces image
Diffuse reflect
When light rays reflect in different directions to each other and scattered
On a rough surface
No image produced
White light
Made up of the whole colour spectrum = a mixture
What happens when white light passes through a prism
Splits into a spectrum
What does the colour of an object depend on?
Which wavelengths of light are transmitted, reflected or absorbed
The colour the object is will reflect that wavelength and absorb all others
How do colour filters work?
Absorb all other wavelengths and only transmit the specific one it is a filter of
If an object can transmit light what does that mean?
You can see right through it
Aka glass
Transparent
Easily see through
Translucent
Scatter light rays
No see through able
If an object can not be seen through what does that mean?
It is opaque
Why do white objects appear white
Reflect all wavelengths of visible light equally
Why do black objects appear black
Because they absorb all wavelengths of visible light equally
Why do red objects appear red
Because it absorbs all wavelengths of visible light
Except frequency of red which is reflected
Putting an object behind a filter of the same colour
Only that light wavelength allowed through
And then reflected off the object so still appears that colour
Putting an object behind a filter of a different colour
The light wave will be absorbed by the object
So no light will be reflected
And appear black
Best absorbers and emitters of infrared radiation
Matte black surfaces
What object will emit more radiation in a given time?
A hot one over a cold one
What does the wavelength and intensity of radiation depend on when emitted?
The temperature of the object
What do hotter objects emit (infrared)
Higher intensity waves
Smaller wavelengths
Why do very hot objects produce visible light?
Because they produce short length infrared radiation
So may even be visible light
Black body radiation
All electromagnetic waves are absorbed
NONE is reflected nor transmitted
Also best possible emitter of them
How do objects increase in temperature?
If it is originally colder than surroundings
It will absorb more radiation than emits
How do objects decrease in temperature?
If it is originally hotter than surroundings
It will emit more radiation than absorbs so decreases
How do objects remain at a constant temperature?
If at the same temp as surroundings, it will emit and absorb radiation at the same rate
How does earth heat energy?
The sun emits short length radiation that can be reflected by clouds
Or absorbed by earth’s surface
To increase temperature
What does earth do when absorbed sun’s infrared radiation?
Emits infrared radiation back into space
But some trapped by greenhouse gases so increases temperature
What other factors affect earth temperature surface?
Cloud cover
Because more clouds will reflect infrared radiation back down to earth rather than radiating it to space
