P14 Light Flashcards
What is the Law of Reflection?
Angle of Incidence = Angle of Reflection
What is the “Normal”?
The line perpendicular to the mirror
What is the angle of incidence?
The angle between the incidence ray and the normal.
What is the angel of reflection?
The angle between the reflected ray and the normal.
What is refraction?
The changing direction of a wave (light) as it travels between mediums of different densities
What makes a colour?
Visible light with it’s own narrow band of wavelength and frequency.
What is specular reflection?
Reflection from a smooth surface in a single direction.
What is diffuse reflection?
Relfection from a rough surface causing scattering
How do colour filters work?
By absorbing certain wavelengths of visible light (colours) and transmitting other wavelengths of visible light (colour).
What is the colour of an opaque object determined by?
It’s determined by which wavelengths of light (colour) are more strongly reflected.
What happens to wavelengths which are not reflected?
They are absorbed
What makes an object appear to be white?
If all the wavelengths are reflected equally.
What makes an object appear black?
If all the wavelengths are absorbed
Objects that transmitt light are either ….
… transparent or translucent
What two things change about a wave when it passes between mediums of different densities?
Speed and direction
How does a lens form an image?
By refracting light
How does a convex lens work?
Parallel rays of light converge (join together) to focus at the principal focus.
How does a concave lens work?
Parallel rays diverge (spread out) to focus at the principal focus.
What is the focal length?
The distance from the lens and principal focus
The image produced by a convex lens is …
…. either virtual or real
The image produced by a concave lens is ….
…. always virtual
What is a real image?
When light is converged (comes together) to form an image on a screen or retina.
What is a virtual image?
When light rays diverge so the object appears to be in a different place.
How do you calculate magnification?
Magnification = image height / object height
- magnification is a ratio so it dosen’t have an SI unit
Generally, what should image and object height be measured in?
mm or cm if measurement isn’t specified
In a ray diagram how is a convex lens represented?
An line with arrow heads (<—->)
In a ray diagram, how is a concave lens represented?
A line with “V” heads (>—–<)
How do you draw a ray diagram for an image through a convex lens?
- from the top point of the object draw a line parallel going to the lens
- draw a second converging refracted line passing through the principal focus
- draw a third line from the top point of the object right through the middle of the lens
(note : these steps are done because light is being converged)
How do you draw a ray diagram for an image through a concave lens?
- from the top point of the object draw a line parallel going to the lens
- draw a second diverging refracted line passing through the principal focus
- draw a third line from the top point of the object right through the middle of the lens
(note : these steps are being done because light is being diverged)
How do you find the refractive index?
Sin(i) / Sin(r)
What can refractive index tell us?
How much slower light travels through a medium compared to a vacuum or air (which is 1)
What is the critical angle?
The angle of incidence when Total Internal Reflection is achieved.
- *above this all light is reflected, no light is refracted out*
What must happen for Total Internal Relfection (TIR) to occur?
1) Angle of incidence must be larger than the critical angle
2) Ray must be in medium with higher refractive index (‘more optically dense’)
How do you carry out the Light Required Practical?
1) Make a narrow ray of light by slotting a slit into the ray box
2) Place the glass block on top of a piece of paper and trace it.
3) Draw a normal to the block
4) Align the incident ray with the meeting point between the normal and surface of the block.
5) Draw the refracted ray and reflected ray
6) Using a protractor measure the angle of: incidence, reflection and refraction
7) Repeat the experiment with either different material or different incidence
