Unit 4A - Intro. Optics and Light Flashcards
Principles of Light
Light travels in straight lines through air as an electromagnetic wave (at the speed of light), and can travel through space without any medium.
Luminous v. Non-Luminous Sources
- Luminous source: Produces own light
- Non-luminous source: Doesn’t produce own light
Incandescence
- Light from high temperature
- Ex: Heated tungsten wire glowing in lightbulb - Inefficient due to most of energy at tungsten wire lost as heat
Electric Discharge
- Light from passing electric current through gas
- Ex: Lightning
Phosphorescence
- Light by absorption of UV light resulting in emission of visible light over time
- Ex: Glow-in-the-dark stars
Bioluminescence
- Light from organisms as result of chemical reaction with little/no heat produced
- Ex: Fireflies
Fluorescence
- Light by absorption of UV light resulting in immediate emission of visible light
- Ex: Fluorescent bulbs
Chemiluminescence
- Light as result of chemical reaction with little/no heat produced
- Ex: Glow sticks
Triboluminescence
- Light from friction from scratching, crushing, or rubbing crystals
- Ex: Light from quartz crystals
Light from Light-Emitting Diode
- Light produced by electric current in semiconductors
- Ex: LED bulbs
- More energy efficient
Normal
The perpendicular line to a mirror surface
Geometric Optics
The use of light rays to determine how light behaves when it strikes objects
Degrees of Visibility
- Opaque: Cannot be seen through at all
- Translucent: Can be seen through at any degree except completely
- Transparent: Can be seen through completely
Components of Mirror
- Sheet of glass and thin film of reflective silver/aluminum
- Glass protects thin film on the back and aids physical appearance of mirror.
- Thin film reflects light
Real Image
Image formed when light rays meet at particular point after reflection from mirror
Virtual Image
Image in which light does not actually arrive at or come from the image location
Laws of Reflection
- Flat Surfaces: Angle of incidence = Angle of reflection
- Incident ray, reflected ray, and normal all lie on same plane
Image Attributes from a Plane Mirror
- Size: Same [as object]
- Attitude: Upright
- Location: Behind mirror
- Type: Virtual
Centre of Curvature “C”
Centre of the sphere of which the curved mirror forms a part
Principal Axis
Straight line passing through centre of curvature and focal point
Vertex “V”
- The midpoint of the mirror
- The point where the principal axis intersects the mirror
Focus “F”
Point where all light rays parallel to principal axis reflected off converge
Rules for Concave (Converging) Mirrors
- Light ray parallel to principal axis reflected through focus
- Light ray through center of curvature reflected back on itself
- Ray through F will reflect parallel to principal axis
- Ray at vertex will follow law of reflection
Reversibility of Light
Switching the incident and reflected rays of light will still lead the light to follow the same path
Object Beyond C, At C or Between C and F
Reflected rays meet in front of mirror, forming inverted real image
Object Located At F
Reflected rays parallel and do not intersect neither in front of nor behind the mirror
Object Between F and Concave Mirror
Reflected rays diverge, leading brain to extrapolate diverging rays backward to appearance of origin behind the mirror
Object Beyond C
Image smaller, inverted, between C and F, real
Object Between C and F
Image larger, inverted, beyond C, real
Object at C
Image same size, inverted, at C, real
Object at F
No clear image
Object For Concave Mirrors
Image smaller, upright, behind mirror, virtual
Rules for Convex (Diverging) Mirrors
- Ray parallel to principal axis reflected as if it came through focus
- Ray aimed at centre of curvature is reflected back upon itself
- Ray aimed at virtual focus is reflected parallel to principal axis
Images for Convex Mirrors
- Reflected rays from object never cross in front of mirror.
- Brain extrapolates rays behind mirror to where they appear to converge (between virtual focus and vertex)
- Results in smaller, upright virtual image.
Applications of Curved Mirrors
- Concave: Solar cookers, searchlights, satellites
- Convex: Security mirrors, side-view mirrors on cars
Specular v. Diffuse Reflection
- Specular: Reflection off a smooth surface
- Diffuse: Reflection off an irregular/dull surface
Components of a Fluorescent Bulb
- Outer shell: Glass tubing
- 2nd outer shell: Fluorescent coating
- Inner arrow: Direction of current
- Dots: Mercury atoms
- Ends of bulb: Electrode
- Outer arrows: Light
Components of a Glow Stick
- Inner stick: Hydrogen Peroxide Solution held by glass vial
- Inner Surrounding: Phenyl Oxalate Ester and Fluorescent Dye Solution held by plastic casing
How a Glow Stick Works
- 2 chemicals, 1 in a narrow small glass vial
- Bending the stick breaks the vial, causing chemicals to mix
- Chemical reaction produces visible light
Components of an Incandescent Bulb
- Bottom “button”: Electrical foot contact
- Below surface of bottom: Insulation
- Surrounding of bottom: Screw thread contact
- Heated wire: Tungsten filament
- Filament held by: Support wires
- Bulb filled with: Inert gas
The light spectrum
ROYGBIV
Rays of Light (from lowest to highest energy)
- Radio wave > Microwave > Infrared > Visible > UV > X-ray > Gamma Rays
- Higher wavelength, lower energy
Wavelength of Visible Light
Between 380 to 780 nanometres
Focus for Convex Mirror
Virtual Focus
