Light Visible light is a type of energy

Light

Ø Visible light is a type of energy called electromagnetic radiation Ø Electromagnetic radiation is also known as electromagnetic waves What is light? Ø The most talked about form of EM waves are visible light. Stop and Think: What are other types of electromagnetic radiation?

Electromagnetic Radiation The E-M Spectrum organizes waves into different types based on their energies, higher energy waves are more dangers to humans while low energy waves are harmless. Ø Looking at the chart below, where does visible light fit in the spectrum? Using this information, what can you conclude about the energy/danger of microwaves compared to x-rays?

Sources of Electromagnetic Radiation Light is emitted when atoms gain energy, when this happens, we say they are in an excited state. When atom’s release this energy, it is often released as electromagnetic radiation. The different ways in which atoms gain energy are: • Fission/Fusion • Incandescence • Electric Discharge • Fluorescence

Fusion/Fission Nuclear reactions on the sun release energy which excite gas atoms.

Incandescence Ø Incandescent Light is light emitted from a material at high temperature. Ø Typically, electricity generates the heat which excites atoms in the substance. Stop and Think: List 4 sources of incandescent light

Electrical Discharge • An electric current is run through a gas (ex: sodium, mercury) which excites atoms in that vapour.

Fluorescence Ø Florescence is the light emitted by certain materials when exposed to ultraviolet light. Ø A fluorescent bulb is made by coating a gas discharge tube with phosphorus which emits visible light when exposed to UV light

Steps of Fluorescence Fill in using your textbook

Homework Page 407 #1, 2