Lightwaves Flashcards
What are electromagnetic waves?
Waves of energy fields, magnetic and electric, oscillate perpendicular to each other and propagate in a direction perpendicular to their oscillations
What speed does EMR travel at and what range of wavelengths does visible light exist in?
EMR travels at the speed of light in air/vacuum which is 2.998E+8.
Visible light exists in a range from ~700nm to ~400nm
How is the direction of polarization determined?
Polarization is determined by the direction of the electric field, purely by convention
How does the intensity of light change as unpolarized passes through one polarizer?
The light intensity goes down by one-half.
What is Brewster’s Angle?
At this specific angle, the reflected light is completely polarized and refracted light is partially polarized. The two light rays are perpendicular.
Why does light (notably white light) experience dispersion when it enters a new medium?
Different frequencies of light have different indexes of refraction. Thus, no visible wavelength of light will bend the exact same as another.
Note: n decreases and wavelength increases
What does normal dispersion look like?
As white light enters a new medium, the red wavelength will bend the least as it will have the lowest n. For decreasing wavelengths, they will bend more as n increases, resulting in the violet wavelengths bending the most.
How are rainbows formed?
Water droplets are dispersive materials that can refract light similar to a prism. So at the right angles, the light will leave the raindrop as a bow of colours.
What are phase and group velocities?
Group velocity is the velocity at which a wave envelope or wave packet moves.
Phase velocity is the velocity that a constant phase moves.
How can you tell the type of dispersion occurring using Vg and Vp?
If Vp>Vg then the light is undergoing normal dispersion. If the opposite relationship (Vp<Vg) is true then the light is undergoing anomalous dispersion.
Note: if Vg=Vp, there is no dispersion
What is anomalous dispersion?
In this case, shorter wavelengths posses lower indexes of refraction and more at high speeds. This is a clear contradiction to normal dispersion
Does frequency change as a wave (EMR) enters a new medium? If not, what does change and how?
No, the frequency will be constant. It is the wavelength and speed of the EMR that will change. When the new medium has a higher n, the speed and wavelength will decrease.
For reflections, how does the phase change between the incident and reflected wave, when a wave strikes a medium with a different n?
For an increase in n, the phase changes by pi
For a decrease in n, there is no phase change.
What are Newton’s Rings?
In a curved glass wedge, light rays are reflected and interfere to form a pattern of rings that shrink as they move outward. There is a notable dark circle in the middle which is where the light undergoes destructive interference in a large area.
How does an interferometer work?
It’s an instrument used to measure short distances. Basically, a half-silvered mirror splits a light ray into 2 paths. This sends them in perpendicular directions toward mirrors and then follows that path back to a screen. On the screen, you can observe a bright circle (constructive interference) or dark circles (destructive interference) when the mirror is moved so that the path length changes by half a wavelength. [easier to visualize, try answering with an image next to you]
