P14 Light Flashcards
What is the RULE for all reflection RAY DIAGRAMS?
Angle of incidence = Angle of reflection
- the ‘normal’ is the imaginary line perpendicular to the boundary
- the angle of incidence is the angle between the incoming ray and the normal
- the angle of reflection is the angle between the ‘normal’ and the reflected ray
What is specular reflection?
When a wave is reflected in a single direction by a smooth surface
E.g. when light is reflected by a mirror and you get a clear reflection
What us Diffuse reflection?
When a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions
The rule - (Angle of incidence = angle of reflection) still applies
What is refraction?
- When a wave crosses a boundary between materials at an angle, it changes direction
- how much it changes direction depends on how much the wave speeds up or slows down
- this depends on the density of the material
How do you talk about the change in direction of a wave
- If a wave crosses a boundary at an angle and slows down, it will bend towards the normal
- If it speeds up then it will bend away from the normal
(The ‘normal’ is perpendicular to the boundary)
What happens to the wavelength and the frequency when a wave is refracted?
- Wavelength will change
- Frequency will stay the same
When is a wave NOT refracted but still crosses a boundary
When the wave is travelling along the ‘normal’
What is optical density?
- Optical density is a measure of how quickly light can travel through it
- The more optically dense material, the slower the light waves travel through it
What are the 2 main types of lens?
Convex () and concave )(
What is a convex lens?
- A convex lens bulges outwards ()
- It causes light rays that are parallel to the axis to be brought together (converge) at the principal focus
What is a concave lens?
- A concave lens caves inwards )(
- It causes light rays to spread out (diverge)
What is the ‘axis’ of a lens
A line passing though the centre of the lens
What is the principal focus for a CONCAVE lens?
- The point where rays hitting the lens parallel to the axis appear to all come from
- You can trace the refracted rays back to the principal of focus
What is the focal length?
The distance from the centre of a lens to the principal focus is the focal length.
What are the 3 RULES for refraction in a 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 of the ray carries on in the same direction.
What are the 3 RULES for refraction in a convex lens )(
- An incident ray parallel to the axis refracts through the lens and travels in line with the principal focus so it appears to come from the principal focus
- An incident ray passing through the lens towards the centre of principal focus refracts through the lens and travels parallel to the axis
- An incident ray passing through the centre of the lens carries on in the same direction
What lenses produce what images?
- The image produced by a convex lens can be either real or virtual.
- The image produced by a concave lens is always virtual.
What is the equation for magnafication?
IAM triangle
Magnification = image height / object height
How do colour filters work?
Colour filters work by absorbing certain wavelengths (and colour)
and transmitting other wavelengths (and colour).
How are objects black or white?
Black objects absorb all wavelengths of visible light. Your eyes see black as a lack of visible light
White objects reflect all wavelengths of visible light equally
What are objects that transmit light called?
Partially transmit light - Translucent
Fully transmit light - Transparent
Draw a ray diagram for a convex lens
Cool
Check in cgp
Draw ray diagram for a concave lens
Cool check cgp
What determines the colour of an opaque object?
The wavelengths of light that are most strongly reflected
