Light and Optics Flashcards
What are the three basic observable properties of light?
- Light travels in straight lines
- Light rays obey the laws of geometry
- Light travels at a constant speed in a specific medium
Light can either be ___________(1) or _______________(2)
(1) Emitted from a source in every direction(sun, stars, light bulb)
(2) Reflected off an object(Mirror, whiteboard, planet)
What evidence is there to prove the light travels in straight lines?
- Light creates shadows
- Light does not appear to bend around corners
What is the Law of Reflection?
The law of reflection states that the angle of incidence is equal to the angle of reflection.
What did Galileo Galilei do?
- Attempted to find c by measuring the time required for light to travel a known distance between two loops
- Futile experiment because the human reaction rate is far too slow to be able to measure the extremely fast speed of light
- Concluded that c was very fast, possibly infinitely fast
What did Ole Romer do?
- Did not do anything to actually determine the speed of light
- Observed that the period of revolution(the time it takes to complete one full cycle) of Jupiter’s moon Io varied slightly depending on the relative motion between the Earth and Jupiter
- When the Earth is moving away from Jupiter, T is larger
- When the Earth is moving towards Jupiter, T is smaller
Note: T does not get significantly larger or smaller; the difference is quite small.
What did Christian Huygens do?
- Took Romer’s idea and use it to determine a value for the speed of light
- Determined that the speed of light has a finite value and isn’t infinitely small
- Reasoned that there should be a time difference(for when Io was expected to first appear) based on the position of the Earth(in its orbit around the sun) relative to Jupiter.
- Number was closer to the speed of light in water so it was not totally accurate
- cause of error: not having sophisticated enough equipment to measure, the fact that Jupiter also moves in its orbit when the earth is closest/furthest from Jupiter(i.e. Jupiter is not in a stationary position so the distance would not be from the same point)
What did Albert Michelson do? What equation did he derive in terms of d, n, and f
- Used a rotating mirror apparatus with n sides
- An observer will always view the returning beam of light through a small telescope only if the rotating mirror turns at a specific frequency
equation derivation:
c= d/t
= 2d/(T/n)
= 2dn/T
= 2dnf
What is a centre of curvature?
The centre of the sphere
What is the vertex?
The geometric centre of the curved mirror surface
What is the principal axis?
An imaginary line that extends outwards from the vertex to the centre of curvature
What is the focal point?
Half the distance from vertex to curvature
What is the normal line?
Always represented by the radius of the sphere
What is a virtual image?
Images that exist inside of the mirror(i.e. you can not physically touch these images)
What is a real image?
Are formed as a result of light reflecting off of a mirror and onto a screen outside of the mirror(i.e. projector)
What is a concave mirror and how do light rays reflect off this type of mirror?
With a concave mirror, or a converging mirror, light rays strike the inner surface of the surface and reflect towards a real focal point
What is a convex mirror and how do light rays strike/reflect off this type of mirror?
With a convex mirror, or a diverging mirror, light rays strike the outer surface of the sphere and reflect away from a virtual focal point.
What are the three rays that can be used to create an image?
- An incident ray parallel to the principal axis will reflect through(or away from) the focal point
- An incident ray that passes through(or is headed for) the focal point will reflect parallel to the principal axis
- An incident ray that passes through(or is headed for) the centre of curvature will reflect back through(or away from) the centre of curvature
What is the sign convention for the focal length f with mirrors?
- Positive for concave or converging mirrors
- Negative for convex or diverging mirrors
What is the sign convention for d(o) with mirrors?
Always positive because the object is always on the real side