light .1

• Light


  Travels in straight lines
• Laser


  • A ray of light is represented by a straight line
• Beam


  A collection of rays
• Types of beams of light


  • Parallel beams - collection of parallel rays
  • Divergent beams - rays that spreads out from a point
  • Convergent beams - rays that come to focus
• Beam types


  • Torch light creates a divergent beam
  • Headlights on a car creates parallel beams
  • A magnifying glass creates convergent beams
• Light travels around 300,000,000 metres per second
• At this speed light can go around the world 8 times in one second
• Light travels much faster than sound


  For example, thunder and lightning start at the same time, but we will see the lightning first
• When a starting pistol is fired


  We see the smoke first and then hear the bang
• Reflect


  We see things because they reflect light into our eyes
• Luminous object


  One that produces light
• Non-luminous object


  One that reflects light
• Luminous objects


  • The Sun
  • Lamps
  • Lights
  • Lasers
  • Campfires
• Reflectors


  • The Moon
  • Mirrors
  • People
  • Objects
• Shadow


  Places where light is "blocked"
• When light is totally or partially absorbed, a shadow is formed
• Point source


  If the light source is small compared to the size of the object, then the shadow will be SHARP
• Extended or large source


  If the light source is of comparable size to the object, then the shadow will be "fuzzy"
• Umbra


  The dark inner region of the shadow
• Penumbra


  The grey region of the shadow
• Eclipse


  Occurs any time something passes in front of the Sun, blocking its light
• Lunar eclipse


  The Earth moves between the Sun and the Moon, blocking the Sun's light, and causing the moon to glow red
• The Sun acts as an extended source of light
• Partial solar eclipse


  Visible if you are in the penumbra of the shadow, only some of the Sun will be blocked by the Moon
• Total solar eclipse


  Can only occur if you are at the exact spot within the moon's umbra
• Pinhole camera


  A camera without a lens which uses a very small hole pierced in one end to allow light to pass through, forming an upside down image on the back
• Light rays from an object pass through a small hole to form a sharp image
• If the pinhole is made larger the image is made blurry & bright as more light enters
• Multiple holes will produce multiple images
• Decreasing the distance between the object and the pinhole increases the image size
• Lunar Eclipse


  Occurs when the Earth moves between the Sun and the Moon, blocking the Sun's light and causing the moon to appear reddish. This can only happen during a full moon.
• Solar Eclipse


  Occurs when the Moon moves between the Earth and the Sun, blocking the Sun's light and causing a shadow to fall on the Earth. This can only happen during a new moon.