Light, Camera, Reflection (8J Science)

• Light


  • Travels in straight lines from a source
  • Travels as transverse waves
  • Travels much faster than sound
  • Does not need a substance to travel through
• Transparent objects


  Allow light to pass through
• Opaque objects


  Block all light
• Translucent objects


  Allow some light to pass through, but it is scattered so you do not see a clear image
• Shadows


  Made when light is blocked by an object
• Transparent materials


  Let light pass straight through, we say they transmit light
• Opaque surfaces


  Can absorb or reflect light
• White surfaces


  Reflect most of the light that hits them
• Black surfaces


  Absorb light very well and reflect very little
• Diffuse reflection


  • Light rays are scattered by rough surfaces, you cannot see an image in an object with a rough surface
• Specular reflection


  • Mirrors and shiny materials such as polished metals reflect light evenly
• Law of reflection


  The angle of incidence (θ) is equal to the angle of reflection (r)
• Normal


  A line drawn at right angles to the reflecting surface
• Image in a plane mirror

  Same size as the object, same distance away from the mirror, left becomes right and right becomes left
• Refraction


  When light hits something transparent it changes speed and direction
• Refraction takes place at the interface between two substances
• When light is transmitted through a transparent substance, it can change direction
• Lenses


  Curved pieces of glass or transparent plastic that are designed to refract light in particular ways
• Converging lenses


  • Make rays of light come together
  • The focal point is where parallel rays of light are brought together by the lens
  • The focal length is the distance of this point from the centre of the lens
• Lenses used in


  • Cameras
  • Microscopes
  • Telescopes
• Rod cells


  Detect faint light but not colours
• Cone cells


  Detect the primary colours of red, blue and green
• Secondary colours


  Combinations of primary colours (magenta, cyan, yellow)
• White light


  A mixture of colours
• Dispersion


  White light can be split up using a prism to give a spectrum of seven colours (red, orange, yellow, green, blue, indigo, violet)
• Objects do not reflect all the colours in light
• Black objects absorb all colours
• Filters


  Transmit one of the colours in white light and let the other colours through
• Looking at a coloured object in coloured light


  The colour may appear different
• Examples of hormones include insulin (regulates blood sugar levels), thyroid hormone (controls metabolism), adrenaline (involved in fight or flight response), growth hormone (promotes growth and development), oxytocin (stimulates uterus contractions during childbirth and milk ejection during breastfeeding), and cortisol (manages stress).