1. 10.1
What is Light?

2. What is Light?
The sun emits large amounts of energy in all directions. Some of this solar energy reaches Earth and heats the Earth’s surface.
SOURCES:
a. Natural
ex: sun, fireflies
b. Artificial
– man made/controlled
ex: electric bulb, and
flashlight

3. Light Energy Light is a form of energy.
We use light energy for many things:
-light our homes/schools
-technology converts light energy into thermal energy to heat our homes and water.
Energy from the Sun is called solar radiation.
To reach us this radiation has to pass through space, which is a vacuum (there is no matter in a vaccuum not even air).

4. THE SUN the most abundant source of light
hydrogen atoms in the Sun’s core have so much energy that when they collide, they sometimes combine to form helium (this process is called a fusion reaction)
a tremendous amount of energy is released from a fusion reaction
the fusion energy is transmitted to the gases on the outer layers of the Sun
when these excited atoms release some of their excess energy, they emit light
fusion energy is a form of nuclear energy

5. Light from INCANDESCENCE
incandescence is light emitted from a material because of the high temperature of the material
for many years, the most common source of light at home USED to be the incandescent light bulb
an incandescent bulb has a tiny tungsten wire that gets very hot and glows brightly when electric current runs through it (thus electrical energy generates the heat that excites the atoms)
an incandescent bulb is inefficient at producing light—only about 5% of the electrical energy used in an incandescent bulb becomes light (the remaining 95% is lost as heat)

6. Light from ELECTRIC DISCHARGE Light from ELECTRIC DISCHARGE Light from ELECTRIC DISCHARGE Light from ELECTRIC DISCHARGE Light from ELECTRIC DISCHARGE Light from ELECTRIC DISCHARGE
found in some street lights; lightning
light is emitted from a heated gas (or vapour) instead of a heated wire
this process is called electric discharge
a common form of the electric discharge bulb is the sodium vapour bulb
there is an electrode at each end of the bulb
a drop of sodium and a small amount of mercury is placed in the bulb
most of the air is removed from the bulb, and then some of the sodium and mercury form a vapour in the bulb
an electric current passes through the vapour and excites the atoms
when the excited atoms release their energy, you see as a characteristic yellow

7. FLUORESENCE FLUORESENCE FLUORESENCE
fluorescence is a light that is emitted during exposure of the source to ultraviolet light
a fluorescent bulb is an electric discharge tube with an electrode at each end
the bulb contains mercury vapour and an inert gas (ex.: argon, a noble gas)
because the bulb contains mercury, the fluorescent bulbs need to be disposed of properly (ex: at hazardous waste centres)
the inside of the bulb is coated with a powdery substance, phosphor
when electrical energy charges the electrodes (at each end), they emit electrons
the electrons travel through the gas, from one electrode to the other
as the electrons travel through the gas, they collide with atoms of mercury and excite these atoms
the excited mercury atoms release their energy in the form of UV light (which human eyes can’t see)
the energy of the UV light is absorbed by the phosphor, which emits visible light

8. LUMINESCENCE LUMINESCENCE LUMINESCENCE
the emission of light by a material or object that has not been heated (ex.: fluorescence—uses UV light to excite atoms of the phosphor)
opposite of incandescence
types of luminescence:
fluorescence
phosphorescence—light that is emitted due to exposure of the source to UV light, and that continues to be emitted for some time in the absence of the UV light
similar to fluorescence, except the excited atoms in the phosphorescent material retain the energy for several minutes (or even hours)
the phosphorescent materials glow long after they have absorbed the UV light (ex.: glow in the dark objects)
chemiluminescence—light that is produced by a chemical reaction without a rise in temperature
the energy of a chemical reaction causes the light to be generated
ex.: glow sticks—two different chemicals are in the stick (one is inside and one is outside a glass capsule); when the glow stick bends, the glass capsule breaks and the 2 chemicals combine; dye in the solutions cause the colour of the light (red dye, yellow dye, blue dye etc.)
bioluminescence—light that is produced by a biochemical reaction in a living organism
chemical reactions in the living cells produce the light
common in marine animals (krill, jellyfish, deep-sea starfish, black dragonfish)

9. THE NATURE OF LIGHT THE NATURE OF LIGHT THE NATURE OF LIGHT THE NATURE OF LIGHT THE NATURE OF LIGHT
light is the only form of energy that can travel like a wave through empty space and through some materials
light behaves like a special kind of wave, called an electromagnetic wave
electromagnetic waves involve the movement of energy from one point to another
a wave length is the distance from one crest (or trough) of a wave to the next crest (or trough)
electromagnetic waves are invisible and can travel through a vacuum—they don’t need particles in order to travel
they travel through a vacuum, such as space, at the speed of light (3.00 x 108 m/s)

10. THE ELECTROMAGNETIC SPECTRUM
EMR
is a diagram that illustrates the range (or spectrum) of electromagnetic waves in order of wavelength or frequency
the colours of light are just different wavelengths of light
the colour red has the longest wavelength, while violet has the shortest wavelength of all the visible light

11. Visible Light and Colours
Visible Light - “EMW that we see”
The light we see when we look at a candle flame, a glowing light bulb or the Sun.
Visible light from the Sun and light bulbs appears to be white.
Isaac Newton –first scientist to separate light into its component colours.
Sun through triangular prism
= ROY.G.BIV

12. Visible Spectrum Visible Spectrum-
The continuous sequence of colours that makes up white light.

13. Electromagnetic Spectrum
The classification of electromagnetic waves, arranged from lowest energy to highest energy, which includes visible light.

14. The Electromagnetic Spectrum