What is light?
- A form of energy that the Sun emits in all directions
Properties of Light
- Light travels in straight lines:
- Light travels VERY FAST – around 300,000, 000 metres per second. (3.0 x 108 m/s)
- Light travels much faster than sound. For example: Light energy is transferred through radiation
RADIATION
- A method of energy transfer that does not require a medium
MEDIUM
- Any physical substance that acts as a carrier for the transmission of energy
- Light is an electromagnetic wave
- Electromagnetic waves are based on the
energy of waves. - We use the electromagnetic spectrum as the classification system.
- The electromagnetic spectrum is the complete spectrum or continuum of light.
Radio waves
- Low energy waves with long wavelengths
- Includes FM, AM, radar and TV waves
- Low frequency
- Used in many devices such as remote control items, cell phones, wireless devices, etc.
Microwaves
- Longer than radio, shorter than light and infrared
- First used in radar, now used in communication, medicine and consumer use (microwave ovens)
Infrared light
- Invisible waves that are detected as heat
- Can be detected with special devices such as night goggles
- Used in heat lamps, remote controls, lasers
- Higher energy than microwaves but lower than visible light
Visible Light
- The portion of the electromagnetic spectrum that human eyes can detect
- ROYGBIV (red, orange, yellow, green, blue, indigo, violet)
- Red is the lowest frequency and violet is the highest frequency
- White light is not a single colour; it is made up of a mixture of the seven colours of the rainbow.
- The colour sequence is the visible spectrum
Ultraviolet waves
- Higher energy than light waves
- Causes skin to tan and burn
- Can cause skin cancer and blindness in humans
- Used in tanning beds and sterilizing equipment
X-Rays
- Medical imaging (i.e. used for teeth and bones)
- Security equipment (i.e. luggage scanners)
- High energy waves
- Can cause cancer
Gamma rays
- Highest energy
- Generated by radioactive atoms and in nuclear explosions.
- Can kill living cells
- Gamma rays are used to kill cancerous cells.
- Blocked from Earth’s
- surface by atmosphere
Sources of Light
- Luminous and non-luminous objects
- We see things because they reflect light into our eyes:
Shadows
- Sources of Light (Luminous)
Incandescence
- is the emission of light (visible electromagnetic radiation) as a result of high temperature.
Electric Discharge
- Produced by an electric current passing through a gas
- Different gases produce different colours
- Examples of electric discharge:
- lightning, neon sign
- Examples of gases:
- neon gas produces red colour;
- helium produces gold-colour
- argon produces a pale violet-blue
Fluorescence
- An object absorbs ultraviolet light and immediately releases the energy as visible light.
- Sources of Light
Phosphorescence
- It is the process of producing light by the absorption of ultraviolet light
- It is the emission of visible light over an extended period of time. It can range from seconds to days
- Sources of Light
Chemiluminescence (sometimes “cold light”)
- is the emission of light with limited emission of heat (luminescence), as the result of a chemical reaction.
- Sources of Light
Bioluminescence
- is the production and emission of light by a living organism.
- the result of a chemical reaction with little or no heat produced.
- Sources of Light
Triboluminescence
- is the production of light from friction as a result of scratching, crushing, or rubbing certain crystals through the breaking of chemical bonds in the material.
- Sources of Light
Light from Light-Emitting Diode (LED)
- An electronic device that allows an electric current to flow in only one direction.
- It does not require a filament.
- It does not produce much heat.
- Energy efficient
