Science

• Luminous objects


  Can be seen because the light they emit enters our eyes
• Non-luminous objects


  Can be seen as some of the light they reflect enters our eyes
• Luminous objects


  • Sun
• Non-luminous objects


  • Moon
• Seeing luminous objects


  Light from luminous source travels directly to eye
• Seeing non-luminous objects


  Light from luminous source hits non-luminous object and reflects into eye
• Light travels in straight lines and cannot bend around corners
• Shadows are formed because light cannot pass through opaque objects
• Size of shadow


  Depends on distance of light source from object and angle of light rays
• Reflection


  Change in direction of a ray of light when it hits a surface
• Angle of incidence = angle of reflection
• Transparent objects allow light to pass through completely</b>
• Translucent objects allow some light to pass through
• Opaque objects do not allow any light to pass through
• Transparent objects


  • Glass
• Translucent objects


  • Frosted glass
• Opaque objects


  • Wood
• Why transparent materials are used for windows and spectacles


  To allow light to pass through completely
• Why translucent materials are used for bathroom windows


  To allow some light to pass through while providing privacy
• Why opaque materials are used for walls


  To block all light and provide privacy/security
• Liquids and gases can also be opaque
• Reflected ray


  The ray which is reflected back (bounces off) from the surface
• Angle of incidence


  The angle at which light falls onto the surface
• Angle of reflection


  The angle at which light is reflected from the surface
• The angle of incidence is the same as the angle of reflection
• Regular reflection


  1. Light hits the smooth surface (e.g. mirror) and is reflected back

  2. Reflected rays reach our eyes and we see an image, a reflection
• In regular reflection, the angle of incidence is equal to the angle of reflection
• Irregular reflection


  1. Incident rays from the light source hit the rough surface (e.g. sand, rock)

  2. Reflected rays are scattered

  3. Not all reflected rays reach the eye and we do not see a clear reflection
• Smooth surfaces


  Reflect light well enough for us to see an image on the surface
• Rough surfaces


  Reflect light in a disorganized way
• Periscope


  • Optical instrument used to see over high objects or around corners
  • Contains two plane mirrors that change the direction of light and its rays
  • When the reflected rays reach our eyes, we are able to see an image of the actual object
  • Used in submarines to see objects out of water, while remaining under sea level
• White light is really made up of different colours
• When white light hits an object


  The object absorbs all the colours except for the one we see the object in
• White surfaces reflect all the light, whilst black surfaces do not reflect any light at all
• Eyelid


  Acts like a shutter to stop light from entering the eye, and when we blink it acts like a wiper, removing dust and distributing a film of tears on the surface
• Sclera


  The white part of the eye which acts as the supporting wall of the eyeball
• Eyelashes


  Stop dust and sweat from entering our eyes
• Iris


  The coloured ring of muscle that controls the size of the pupil
• Pupil


  A hole in the iris which lets light in
• Cornea


  Thick layer of transparent cells that protect the eye