science grade 8 - light

WHAT IS LIGHT

LIGHT

� Artificial Light � Light that people have created � Examples: Light bulb, glow

stick � Natural Light

� The most abundant and cheapest form of light

� Examples: Sun, fire � Radiation

�  This does not require matter

PRINCIPLES OF LIGHT

� 1. Light is a form of energy! � 2. Light that is absorbed by a surface can be

transformed into thermal energy, electrical energy or chemical energy.

INCANDESCENT SOURCES

� Object heated to a point where it emits light

� Inefficient � 95% of energy is lost as heat

� Energy Transformation: � Electrical Energy Thermal

Energy Visible Light Energy � Examples:

� Light bulb, candle flame, fire.

FLUORESCENT SOURCE

� Under a black light, white looks like it is glowing.

� Fluorescence is ultraviolet light being absorbed and reflected by particles in fabric.

� Page #181 -Diagram

FLORESCENT ENERGY TRANSFORMATION

� Summarized � Ultraviolet Light Energy Energy Absorbed by

Particles Visible Light Energy

� Energy Pathway is: � Electrical Energy Energy Absorbed by mercury

particles Ultraviolet Light Energy Energy Absorbed by Phosphor Particles Visible Light Energy

COMPARISON Incandescent Florescent

PHOSPHORESCENCE SOURCES � Light energy is absorbed by

particles that can store this energy for awhile.

� The persistent emission of light following exposure and removal of source of radiation is called phosphorescence.

� Take longer to emit light and continue to glow for awhile after.

CHEMILUMINESCENT SOURCE �  Light from a chemical reaction

�  Light is produced when the reaction creates significant energy among particles. This results in visible light.

BIOLUMINESCENT SOURCES

�  Light produced through chemical reactions in an animals body.

�  These reactions create energy and thus a source of visible light.

WAYS TO REMEMBER � Phosphorescence = Phosphor coating makes it

glow � Chemiluminescence = Chemical Reaction � Bioluminescence = Biology, study of living things � Can we come up with a way to remember the

energy pathways for florescence? � E � M � U � P � V