P14 Flashcards
What can all waves be?
Absorbed,transmitted or reflected
When a wave arrives at a boundary between two different materials what happens?
- The waves are absorbed by the material the wave is trying to cross into this transferes the energy to the material energy stores
- The waves are transmitted. Refraction happens
- The waves are reflected
Angle of incidence =
Angle of reflection
Whats the angle of incidence?
The angle between the incoming line and normal
Whats the angle of reflection?
The angle between the reflected and the normal
Whats the normal line?
An imaginary line perpindicular to the surface at the point of incidence. Normally the dotted line
When does specular reflection happen?
A wave is reflected in a single direction by a smooth surface.
Give an example of specular reflection?
When light is reflected in the mirror and you get a clear reflection
What is diffuse reflection?
When a wave is reflected by a rough surface and the rays are scattered in different directions
What happenes when loght is reflected by a rough surface?
The surface appears matte and you don’t get a clear reflection of objects
What’s refraction?
Waves changing direction at a boundary
What happens when a wave crosses a boundary at an angle and changes direction?
It refracts
What does how much it refracts depend on?
- How much it speeds up or slows down
- Also density of 2 materials
What does a higher density mean?
It will slow down
What happens when a wave crosses a boundary and slows down?
It will bend towards the normal line
What happens if it crosses into another material and speeds up?
Bend away from the normal line
What happens when the wavelength of a wave stays the same?
The frequency stays the same
What happens if a wave travels across the normal line?
Change speed but not refract
Why do waves go in a different direction?
The wave hit a medium
Whats the optical density?
A measure of How quickly light can travel through it
What does higher the optical density mean?
The slower light waves travel through it
Why should you do the practical in a dim room?
So you can see the light rays better
What materials can you use to investigate refraction?
Transparent
What are the steps for the transparent material?
1) Place a transparent block on a peice of paper and trace around it. And shine a ray box at the block
2) trace the incident ray and mark the emerging ray. Then draw a straight line to each other to show the refracted ray
3) draw the normal when the light enetered the block, use a protractor to measure between the normal and refracted.
4) Repeat using rectangle blocks with different materials keeping the incident ray the same.
Angle of refraction change for different materials
How do lenses form images?
By refracting light and chnaging it’s direction
Whats a convex lens?
Bulges outwards and causes rays of light parallel to the axis to be brought together at the focus point.
Whats a concave lens?
Caves inwards and causes parallel rays of light to spread out
Whats the axis of a lens?
The line passing through the middle of the lens
Whats the principle focus of a convex lens?
Is where rays hitting the lens parallel to the axis all meet
Whats the principle focus of a concave lens?
The point where rays hitting the lens parallel to the axis appear to all come from.
Whats the focal length?
The distance from the centre of the lens to principle focus
What are the 3 rules for refraction in convex lens?
- an incident ray parallel to the axis refracts through the lens and passes through the principal focus on the other side.
- an incident ray passing through the principal focus refracts through the lens and travels parallel to the axis
- an incident ray passing through the centre carrys on
Rules for concave lens?
- An incident ray passing through the centre of the lens carrys on in same direction
- An incident ray passing towards the principal focus refracts through the lens and is parallel to the axis
- An incident ray parallel to the axis refracts through the lens and travels in line with the prinicpal focus
What can lenses produce?
Real and virtual images
What is a real image?
When the light from an object comes together to form an image on the screen like the image formed on the eyes retina
Whats a virtual image?
Is when rays are diverging so the light from the object appears to come from a different place
An example of a virtual image?
When you look in the mirror because the objects behind the mirror
What are the 3 things to describe an image?
- How big is it
- Real or virtual
- Upright or inverted
What lens always creates virtual images?
Concave lens
What uses convex lenses?
Magnifying glasses
Magnification =
Image height/object height
What is visible light made from?
A range of colours
What does each colour have?
Own range of wavelengths and frequencies
How do you make other colours?
By mixing them
What are the ony colours you can get without mixing?
Red,green,blue
What do all different colours create?
White light
What do colour and transparency depend on?
Absorbed wavelengths
What happens when visible light hits an opaque objects?
They absorb some wavelength and reflect others
What does the colour of an opaque object depend on?
Which wavelengths are strongly reflected
What happens to opaque object that aren’t a primary colour?
They reflect on other wavelengths of light corrosponding to that colour
What do white objects reflect.
All visible light equally
What do black objects absorb?
All wavelengths of visible light
What are colour filters used for?
Filter out different wavelenths of light so that only certain colours are transmitted
What does a primary colour transmit?
Only that colour
What happens when a different colour goes through a colour filter ?
Goes black
