Physics

• Laws of Reflection

  • Angle of incidence = angle of reflection
  • Incident ray, reflected ray, and the normal all lie in the same plane
• Specular Reflection

  • Reflection of light off a smooth surface (e.g. mirror, still water, flat piece of aluminum foil)
  • Creates parallel reflected rays with same angles of reflection
• Diffuse Reflection

  • Reflection of light off an irregular or dull surface (e.g. sheet of paper, wavy water surface, crumpled aluminum foil)
  • Incident rays have varying angles of incidence and resulting reflected rays will have differing angles of reflection and will be scattered (not parallel)
• Light

  Form of energy that is transferred through RADIATION (a MEDIUM isn't needed for transfer)
• Light energy can travel through a vacuum (empty space, e.g. no matter) or through matter
• EM RADIATION

  Stream of PHOTONS (no mass or charge, particle-like behaviour) that travel in a wave-like manner at the speed of light
• Photons

  Carry different amounts of energy depending on the type of EM wave
• ELECTROMAGNETIC SPECTRUM

  Classification of all types of EM waves based on their energy
• EM waves

  • Vary based on their wavelength (distance between crests of 2 waves) and the amount of energy they have
  • Longer wavelength less energy
  • Shorter wavelength more energy
• TYPES OF EM waves

  • RADIOWAVES (longest wavelength, least energy) - radio, TV, cellphones
  • MICROWAVES - microwave ovens, communication
  • INFRARED - remote controls, heat detection, food warmers
  • VISIBLE LIGHT - EM waves that human eye can detect (ROYGBIV)
  • ULTRAVIOLET - cause of burns, sterilization, vitamin D production
  • X-RAY - medical imaging, security screening
  • GAMMA RAY (shortest wavelength, highest energy) - cancer treatment, astronomical observation
• Some parts of the EM spectrum have photons that carry enough energy that they can detach e- from atoms or molecules (IONIZING RADIATION) and can cause damage to living tissues (e.g. cancer, burns, death)
• VISIBLE SPECTRUM

  Continuous sequence of colours that make up white light
• As white light passes through a prism

  1. The speed of light slows down

  2. Colours separate due to differences in speed at which they travel

  3. Least energetic lights are slowed the least (red, longest waves), and most energetic are slowed the most (violet, shortest waves)

  4. In a vacuum, all travel at same speed
• LUMINOUS

  Produces its own light (e.g. the Sun, light bulb, lit match)
• NON-LUMINOUS

  Does not produce its own light (only see due to reflected light)
• Ways luminous objects can produce light

  • Incandescence
  • Electric discharge
  • Phosphorescence
  • Fluorescence
  • Chemiluminescence
  • Bioluminescence
  • Triboluminescence
  • Light-emitting diode (LED)
• Incandescence

  Due to high temperature (e.g. stove burners and elements, filament in light bulb - very inefficient, emits infrared energy = heat)
• Electric discharge

  Electric current passing through a gas (e.g. lightning, "neon" lights)
• Phosphorescence

  Absorption of UV light followed by the emission of visible light over time (Phosphors absorb UV light, keep some of the energy, and release lower energy visible light over time, e.g. "glow in the dark" items)
• Fluorescence

  Absorption of UV light followed by the immediate emission of visible light (e.g. whitening laundry detergents, highlighters, fluorescent bulbs)
• Chemiluminescence

  Due to a chemical reaction (with little or no heat produced)
• Bioluminescence

  Like chemiluminescence, but occurs in living things (for protection, luring prey, attracting mates) (e.g. fireflies, some bacteria, fungi)
• Triboluminescence

  Due to friction as a result of scratching, crushing, or rubbing certain crystals
• Light-emitting diode (LED)

  Due to an electric current flowing in semiconductors (materials that allow electric current to flow in only one direction) - Different from incandescent bulbs as no filament needed, produces little heat, is more energy efficient
• Light Ray

  Line and arrow representing the direction and straight-line path of light
• Geometric Optics

  Use of light rays to determine how light behaves when it strikes objects
• Incident Light

  Light emitted from a source that strikes an object
• How light behaves when it strikes matter

  • Reflected
  • Transmitted
  • Absorbed
• Transparent

  Light easily passes through, and objects behind it are easily seen (e.g. clear glass)
• Translucent

  Some light passes through, but objects behind it can't be seen clearly (e.g. frosted glass)
• Opaque

  Doesn't allow light to pass (reflects or absorbs it), and blocks the view of objects behind it
• Image

  Reproduction of an object through the use of light
• Reflection

  Bouncing back of light from a surface
• Mirror

  Polished surface reflecting an image
• Mirror

  • Front is sheet of glass, and back is a thin layer of reflective aluminum or silver
• Plane Mirror

  Flat mirror
• Incident Ray

  Incoming ray that strikes a surface
• Reflected Ray

  Ray that bounces off a reflective surface
• Normal

  Perpendicular (right angles) line to mirror surface
• Angle of Incidence

  Angle between incident ray and the normal