• Light is a type of energy

• Materials can be transparent, translucent or opaque
• Transparent – light can travel through the material and you can see an image through it
• Translucent – some light can travel through the material but you cannot see an image through it
• You can measure translucency with a light sensor and a bright light

• Opaque – light cannot travel through at all

• Light always travels in straight lines

• Light can change direction
• Lenses are transparent and have curved surfaces
• Two types of lens are:
• Concave
  • Concave lenses diminish (make smaller) things seen through them
  • Concave lenses make parallel beams of light diverge (move apart)

• Convex
  • Convex lenses magnify (make bigger) things seen through them
  • Convex lenses make parallel beams of light converge (move together)
  • The light rays meet at the focal point
  • The distance from the centre of the leans to the focal point is called the focal length

• Lenses are found in:

• Light is made up of a mixture of all colours
  • A prism is a triangular block of transparent material
  • When light passes through a prism the light splits up into its separate colours.
  • This is called a spectrum.

• Make sure you know these colours in order –
  • “Richard Of York Gained Battles In Vain”
    

• Coloured materials absorb (take in) some colours and reflect (bounce off) others
  • E.g. a red object absorbs orange, yellow, green indigo and violet colours and only reflects red.

• Coloured filters are transparent and absorb certain colours of light from white light while transmitting (letting pass through) the rest
• For example a red filter absorbs all colours apart from red which it transmits.

SOUND

• Sound is a type of energy
  • Sound is caused by vibrations in the air or in another material
  • The number of waves passing a point in a second is called the frequency or pitch of the note
  • The higher the frequency the higher the pitch
  • Frequency is measured in Hertz (Hz) (waves per second)
  • The lowest note we can hear is about 20 Hz and the highest is 20;kHz (kilohertz – 20,000 Hz)

• The loudness of a sound is measured in decibels (dB)
  • The loudness of a sound is its amplitude
  • A sound wave can be represented as a wave
  • We describe this shape as sinusoidal

• A is the amplitude.
• This table will give you an idea about the loudness of some sounds – do not learn these values!

• Sounds which are too loud for too long can damage your hearing.
  • The damage is permanent and you will never recover from it
  • To give you an idea the bar below gives you safe exposure limits.; Don’t try to learn these values!

• Some material absorb sounds
• Ear protectors and the walls of recording studios absorb sound well