1 0 1 What is Light The sun emits large amounts of energy in all directions Some of this solar energy reaches Earth and heats the Earths surface SOURCES a Natural ex sun fireflies ID: 545148
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What is Light?
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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, firefliesb. Artificial – man made/controlled ex: electric bulb, andflashlightSlide3
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). Slide4
THE SUNthe 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 Sunwhen these excited atoms release some of their excess energy, they emit lightfusion energy is a form of nuclear energySlide5
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)Slide6
Light from ELECTRIC DISCHARGE
Light from ELECTRIC DISCHARGE
Light from ELECTRIC DISCHARGE
Light from ELECTRIC DISCHARGE Light from ELECTRIC DISCHARGELight from ELECTRIC DISCHARGEfound in some street lights; lightninglight is emitted from a heated gas (or vapour) instead of a heated wirethis process is called electric dischargea common form of the electric discharge bulb is the sodium vapour bulbthere is an electrode at each end of the bulba drop of sodium and a small amount of mercury is placed in the bulbmost of the air is removed from the bulb, and then some of the sodium and mercury form a vapour in the bulban electric current passes through the vapour and excites the atomswhen the excited atoms release their energy, you see as a characteristic yellowSlide7
FLUORESENCEFLUORESENCE
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 endthe 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, phosphorwhen electrical energy charges the electrodes (at each end), they emit electronsthe electrons travel through the gas, from one electrode to the otheras the electrons travel through the gas, they collide with atoms of mercury and excite these atomsthe 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 lightSlide8
LUMINESCENCELUMINESCENCE
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 incandescencetypes of luminescence:fluorescencephosphorescence—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 lightsimilar 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 temperaturethe energy of a chemical reaction causes the light to be generatedex.: 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 organismchemical reactions in the living cells produce the lightcommon in marine animals (krill, jellyfish, deep-sea starfish, black dragonfish)Slide9
THE NATURE OF LIGHTTHE NATURE OF LIGHT
THE NATURE OF LIGHT
THE NATURE OF LIGHT
THE NATURE OF LIGHTlight is the only form of energy that can travel like a wave through empty space and through some materialslight behaves like a special kind of wave, called an electromagnetic waveelectromagnetic waves involve the movement of energy from one point to anothera 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 travelthey travel through a vacuum, such as space, at the speed of light (3.00 x 108 m/s)Slide10
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 lightthe colour red has the longest wavelength, while violet has the shortest wavelength of all the visible lightSlide11
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.BIVSlide12
Visible Spectrum
Visible Spectrum-
The continuous sequence of
colours that makes up white light.Slide13
Electromagnetic Spectrum
Electromagnetic Spectrum-
The classification of electromagnetic waves, arranged from lowest energy to highest energy, which includes visible light.Slide14
The Electromagnetic Spectrum