physics

• The pros and cons have to be weighed up for each individual case when using x-rays and gamma rays in medicine
• Lens


  Focuses and disperses light using refraction
• Lens types


  • Convex
  • Concave
• Convex lens

  Outwards bulge in the center, refracts parallel rays of light inwards to a single point (principal focus), also called a converging lens
• Concave lens


  Caves in on either side, refracts parallel rays of light outwards (disperses the light)
• Principal focus


  Equal distance from the center of the lens on both sides, also called the focal point
• Lenses are symmetrical and can work both ways
• Focal length


  Distance between the principal focus and the center of the lens, shorter focal length means more powerful lens
• Real image


  Light rays actually converge to form the image, can be captured on a screen
• Virtual image


  Light rays don't actually converge, image appears to be where the virtual rays trace back to
• Image properties


  • Real/Virtual
  • Upright/Inverted
  • Bigger/Smaller than object
• Visible light


  Spectrum of different colors from red (longest wavelength, lowest frequency) to violet (shortest wavelength, highest frequency)
• Order of colors in visible light spectrum

  • Red
  • Orange
  • Yellow
  • Green
  • Blue
  • Indigo
  • Violet
• White and black aren't on the visible light spectrum
• White light


  Combination of all wavelengths of visible light
• Blackness


  Absence of light
• Opaque objects


  Don't transmit any light, all wavelengths are either absorbed or reflected
• Opaque object


  • Cat
• Color of opaque object


  Determined by the wavelengths of light it reflects
• Transparent objects


  Transmit most of the light that hits them, almost completely see-through
• Translucent objects


  Transmit some but not all of the light that hits them
• Color of translucent object


  Determined by which wavelengths are transmitted most
• Translucent object


  • Plastic bottle appearing green by transmitting green wavelengths
• Color filters


  Only transmit certain wavelengths of light while absorbing the rest
• Primary color filters


  • Only allow one of the three primary colors (red, green, blue) to be transmitted
• Non-primary color filters


  • Transmit the wavelengths of the same color as the filter, as well as wavelengths of the primary colors that combine to make that color
• An object absorbs radiation


  It will get warmer
• An object emits radiation


  It will cool down
• A hotter object (e.g. cup of tea)


  Emits more radiation than it absorbs, so it loses energy and cools down
• A cooler object (e.g. ice cube)


  Absorbs more radiation than it emits, so it warms up
• An object absorbs and emits the same amount of energy


  It stays at the same temperature
• Intensity


  The power of the radiation per unit of area, a measure of how much energy the radiation transfers to a given area in a certain amount of time
• Graph of emitted radiation

  • X-axis: Wavelength of radiation

  1. axis: Intensity (how much of each wavelength is emitted)
• Types of radiation covered

  • Ultraviolet
  • Visible light
  • Infrared
• As an object's temperature increases


  The intensity of every emitted wavelength increases, and the intensity of shorter wavelengths increases more than longer wavelengths
• Hotter objects (e.g. burning coal, sun)

  Emit more radiation overall and emit shorter wavelengths
• During the day


  The Earth absorbs more energy than it emits, increasing local temperature
• At night


  The Earth emits more energy than it absorbs, decreasing local temperature
• The Earth's overall temperature stays pretty constant as some part is always in the sun
• How sound waves can travel through materials

  1. Sound waves are vibrations that pass through the molecules of a medium

  2. Sound waves travel as a series of compressions and rarefactions

  3. Particles inside a solid vibrate and collide with neighbors to transmit the sound wave

  4. The more densely packed the particles, the faster the sound travels

  5. Sound can't travel through a vacuum