Optics Flashcards
1
Q
Light properties
A
- a form of energy
- travels at 3x108 m/s
- universal speed limit; c in E = mc2
- travels in straight lines
- has wavelike properties
2
Q
Equation for light
A
- v = f x ƛ
- v = speed = (cm/s) or (m/s)
- ƛ = wavelength = Greek letter lambda = (cm/cycle) or (m/cycle)
- f = frequency of waves passing a point = (cycle/second) or (Hz)
3
Q
Visible light
A
- visible light is the portion of the electromagnetic spectrum with wavelengths between 400nm and 700nm
- white light is actually composed of ROYGBIV
- neighbouring types of electromagnetic radiation with longer wavelengths are infra-red, microwaves and radio waves
- electromagnetic radiation with shorter wavelengths (and more energy) includes ultraviolet, X-rays and Gamma Rays
4
Q
Radio stations
A
- FM radio stations broadcast between 88 and 108 MHz
* the station numbers indicate the frequency
5
Q
Colours
A
- each colour has a characteristic wavelength and frequency
- red = long, slow wave (low energy)
- violet = short, fast wave (high energy)
- objects appear coloured due to the wavelengths of light that they reflect
- in a vacuum, all wavelengths in white light travel together and are indistinguishable
- when light enters and exits a prism, each wavelength bends a different amount separating the different wavelengths (colours)
6
Q
Heat
A
• a different form of energy than light
7
Q
Conduction
A
- transfer of heat by fast particles hitting slower ones, speeding them up
- requires a medium
8
Q
Convection
A
- as a fluid is heated its particles push further apart and it expands
- this reduces the fluids density so it rises, conversely, cooler fluids sink by the opposite process
- requires a medium
9
Q
Radiation
A
- causes fluid movement because fluid density changes with thermal expansion
- transmits electromagnetic energy
- doesn’t require a medium and can travel through a vacuum
10
Q
The Ray Model of Light
A
- represents light by a few straight light rays drawn as arrows
- light rays travel in straight lines until they pass through a material or bounce off
11
Q
Transparent
A
Allows light to pass through freely, giving a clear image
12
Q
Translucent
A
Only allows some light rays to pass through, giving a blurry image
13
Q
Opaque
A
Doesn’t light light rays pass through
14
Q
Ray Diagrams
A
- show the path of a few key light rays
- θi = angle of incidence
- θr = angle of reflection
- a normal is an imaginary line perpendicular to the point of reflection
- when measuring angles, measure from the normal to the light ray
15
Q
Laws of reflection
A
- the angle of incidence equals the angle of reflection
* the incident ray, reflected ray, and normal are all in the same plane
16
Q
Regular/specular reflection
A
- occurs when light bounces off a polished surface
* individual light rays obey the law of reflection, and since the normals are parallel, so are the reflected rays
17
Q
Diffuse reflection
A
- occurs when light bounces off an unpolished surface
* individual light rays obey the law of reflection, but since the normals aren’t parallel, the reflected rays scatter
18
Q
Convex/diverging mirrors
A
- reflected rays diverge, but their extensions converge on the far side focal point
- ray 1 = parallel to the principal axis, then extend from the mirror surface through the far focus
- ray 2 = straight to the far focus, then reflect back from the mirror, parallel to the principal axis, extend reflected ray behind the mirror
- image is always upright, smaller, and virtual
- examples = passenger mirror, security mirror
19
Q
Concave/converging mirrors
A
- reflected rays converge on the same side focal point
- ray 1 = parallel to the principal axis, then reflect from the mirror surface through the near focus
- straight through the near focus, then reflect back from the mirror, parallel to the principal axis
- there are several possibilities on the outcome of the image
- examples = make-up mirror, flashlight
20
Q
Refraction
A
- refraction = bending of light as it passes from one medium to another
- the speed of light is constant in any given medium, but changes when light crosses into a different medium
- refraction makes partially submerged solid objects look bent or disjointed
- rainbows are caused by dispersion, the refraction of white light into separate wavelengths
21
Q
Rules for refraction
A
- the incident ray, the refracted ray, and the normal are all in the same plane
- the incident ray and the refracted ray are on opposite sides of the line that separates the two media
- moving from a fast to slow medium, light bends toward the normal (FST)
- moving from a slow to fast medium, light bends away from the normal (SFA)
22
Q
Index of Refraction
A
- a number never less than 1.00
- measures how much light bends when passing from a vacuum to a medium
- a larger refractive index means the medium decreases the speed of light more
- light travels fastest in a vacuum and is assigned a value of 1.00
- since all other media slow light down, they all have a higher index of refraction
23
Q
Equation for Index of Refraction
A
- n = c/v
- n = the refractive index (no unit)
- c = speed of light in a vacuum (3.00 x 108 m/s)
- v = speed of light in the medium
24
Q
Partial Reflection and Refraction
A
- refraction of light is often accompanied by reflection
- example = windows are make to be transparent, but we often see reflections of ourselves in them at the same time
- incident rays striking below the critical angle will reflect and also refract
25
Q
Total internal reflection
A
- at angles of incidence exceeding the critical angle, light will completely reflect back into the slower medium, and no refraction occurs
- jewellery = with a very high index of refraction, diamond has the lowest critical angle that gives diamonds the glittery sparkle
- fiber optics = sending light through thin transparent fibers is a much faster way to transmit digital information than electrons through copper and doesn’t corrode
26
Q
Snell’s Law
A
- n1sinθi = n2sinθr
- n1 = index of refraction of first material
- θi = angle of incidence
- n2 = index of refraction of second material
- θr = angle of refraction
- calculation for critical angle = θr is 90 degrees
27
Q
Concave/diverging Lenses
A
- always forms a smaller, upright, virtual image
- the focal length is positive
- example = peephole
- ray 1 = ray extends to the middle of the lens, refracts away from the principal axis, and its extension passes through the closer focal point
- ray 2 = through the center
28
Q
Convex/converging Lenses
A
- forms different images depending on the location of the object
- the focal length is negative
- example = magnifying glass
- ray 1 = ray extends to the middle of the lens, refracts towards the principal axis passing through the far focal point
- ray 2 = through the center
