Light

1. LIGHT
Electromagnetic Radiation: a combination of electrical and magnetic energy
• Like sound, light travels in waves that have certain wavelengths and frequencies.
• Its speed is different in different materials.
• Light can be reflected or absorbed by certain objects, or it can pass through them.
• Some types of electromagnetic radiation have wavelengths that are shorter than those of
visible light.
ex: ultraviolet, x-ray, & gamma ray radiation
• Longer waves have lower frequencies and lower energies.
ex: infrared waves, microwaves, & radio waves.
• Light is an electromagnetic wave,namely the wavethe vibration of which is electric field and
magnetic field.
• Light is included into transversal wave.
• Light can spread without medium, so light can spread in vacuum.
While several properties of light among other are :
• Spreading according to straight line
• Has energy
• Can be seen
• Radiated in the form of radiation
• Has spreading direction perpendicular to vibration direction
• Can experience reflection, refraction, interference, diffraction, and polarization
Bodies that can spread light is called light source. While bodies that cannot spread light theirself is
called dark body.
 Light rays travel in straight lines from the light source.
 When it hits an opaque object, some light is absorbed and the rest reflects off.
 If the object is transparent, light rays pass through it easily.
If the object is translucent, some light can pass through, but the rest of the light will be reflected
 Light rays travel in straight lines, radiating out from the light source.
 If rays are blocked by an opaque object a shadow forms where the light cannot reach.
 If the light source is moved closer to the object, more light is blocked and a larger shadow is
formed.
SpecularReflection happensif thestreamof lightfallson thebody thatitssurfaceissmooth and shiny,
so direction of the light reflection goes to certain direction.

2. The diffuse reflection happens if the stream of light falls on the body which its surface is rough (not
flat), so the stream of parallel rays which fall on the body will be reflected to every direction.
How Does Light Move?
• Light travels the fastest in a vacuum.
• It travels more slowly through materials such as air or water.
• Moves in straight lines.
• If it reflects off an object light still moves in a straight line but in a different direction.
• Light bends, or refracts, whenever it enters a new material
• White light that enters a prism comes out separated into its colors.
• A rainbow appears in the sky when light reflects and refracts in water droplets.
• An object in the path of light waves casts a shadow.
• The object casting the shadow blocks the path of light.
• A shadow is larger whenn the object is closer to the light source.
CONCAVE vs. CONVEX
Convex Lens: A magnifying glass contains a convex lens that bends light rays
to make objects look larger.
ConcaveLens: A concavelensis thinnerin the middlethan theedges.It can bend lightraysto make
an object look smaller.
Light scatters and looses energy the further away from its source.
SCATTERING: Light released and spreads in all directions.
Sky blue: shortest wavelengths, spread more
ABSORPTION: LIGHT IS TAKEN IN BY AN OBJECT (MATTER) AND HOLDS IT.
• ENERGY TRANSFERRED FROM LIGHT TO HEAT.
• AIR PARTICLES DIMINISH LIGHT.
INTERACTS WITH MATTER
TRANSMISSION: Light goes straight unless changes what it travels through.
• Travels through matter: gases (air), liquids (water) and solid (glass).
Terms for mediums
• Transparent- allows all light through.
• Translucent- allows some light through.
• Opaque- allows no light through.
• CLEAR=TRANSPARENT

3. • SMOKY=TRANSLUCENT
• SOLID=OPAQUE
When Light Strikes an Object
When light strikes an object, the light can be reflected, transmitted, or absorbed
REFRACTION
• The change in direction and speed.
• Moving from water to air, light changes angles and speed of travel.
Refraction of Light
When light rays enter a mediumat an angle, the changein speed causesthe raysto bend,or change
direction
LENSES can’t
CONVEX
-brings image to focal point.
Image is larger and upside down.
i.e.: eye, microscope, magnifying glass.
CONCAVE
-spreads image out.
-image is smaller and upright.
i.e.: corrective glasses
Vision: response to the stimulus of light.
Light with Matter
TRANSMISSION- light going through
REFRACTION-light bending.
ABSORBTION- light absorbed.

4. REFLECTION- light bouncing off.
WAVELENGTH:
Anything that causes a disturbance and transmits energy through matter.
(i.e.: ripple on pond)
FREQUENCY: Number of waves in set time. Decides energy level.
TO SEE COLOR
• Different colors represent different wavelengths.
• Blue- smaller wavelengths
• Red- larger wavelengths
• Color Order: ROY G BIV
If object absorbs then hides color.
• All color absorbed = black
If object absorbs then hides color.
• All color absorbed = black
Wave Properties of Light
 Reflection
 Refraction
 Diffraction
 Interference
Reflection
 when a wave strikes an object and bounces off
 Normal-line perpendicular to the reflecting surface.

5.  Incident ray/incoming ray-the ray that hits the barrier/surface.
 Angle of incidence-angle formed by the incident ray with the normal.
 Angle of reflection-angle formed by the reflected ray with the normal.
Refraction
 bending of waves when passing from one medium to another
 Fiber Optics
 Total Internal Reflection
 when all light is reflected back into the denser medium
 caused by a change in speed
 slower (more dense)  refracted ray bends toward the normal
 faster (less dense)  refracted ray bends away from the normal
Diffraction
 bending of waves around a barrier
 Depends on the wavelength and size of the opening barrier.
Diffraction Gratings
 glass or plastic made up of many tiny parallel slits
 may also be reflective
 spectroscopes, reflective rainbow stickers, CD surfaces Interference
When two waves meets, they have an effect with each other.
 constructive  when the crest of one wave meet the crest of the other one
 constructive  brighter light
 destructive  dimmer light
 interference results from double reflection
 Identify the property of sunglasses that make them useful for wearing on sunny days: The
lenses of the sunglasses are made of a material that allows only some light to pass through
them. It allows the wearer to see while keeping the glaring sunlight out of the eyes.
 Radiation is the wave like transfer of light from its source in all directions.
 Light is often called radiant energy.
 Light from the sun is formed by nuclear fusion.
 The amount of energy a surface receives depends on the intensity of the light.
 The more intense the light, the more light can be absorbed

6.  Incandescent light bulbs produce far more heat than light, or more infrared radiation than
visible light energy. 95% heat vs. 5% light
 Fluorescent bulbs are more efficient. 80% heat vs. 20% light
 The variouscolors of the visible spectrumhaveslightly differentwavelengthsand refractby a
slightly different amount.
 The Primary colors of the visible spectrum are red, green and blue.
 Secondary colors are cyan, magenta and yellow.
 The mixing of three colorsof light to produce many differentcolorsof lightis called thetheory
of color addition.
 Television puts the theory of color addition into practice.
 By changing the brightnessof the dotsthat makeup the screen many different colors can be
produced.
 The television works by fooling the eye into seeing colors that are not really there.
 The colour an object appears depends on the colours of light it reflects.
 For example, a red book only reflects red light:
 A white hat would reflect all seven colours:
 Luminous objects are objects that radiates.
 Most luminous objects release light together with a large amount of heat.
 Non-luminous objects can only be seen if they are reflecting light from a luminous source.
 Light leaves the surface of a luminous object in all directions but if some of the light is made
to pass through a hole it can be seen to travel through a small gap.
 Smaller rays of light are called rays.
 Although the Sun radiates light in all directions, the sides of sunbeams seem almost parallel
because the Sun is a very distant luminous object.
 Non-luminous materials can be classified as transparent, translucent or opaque.
 Transparent materials let light pass through it.
 Translucent materials let some of the light pass through but many light rays are scattered.
 Opaque materials do not let light pass through it.
 A region without light is called a shadow.
 The shapeof theshadowmay notbeidenticalto theshapeof theobjectbecausetheshadow’s
shape depends on the position of the light source and on where the shadow falls.
 The size and intensity of the shadow dependson the size of the light source and the distance
between the light source and the object.
 The way light is reflected froma surfacedependson whetherthesurfaceis smooth or rough.
 The angle of reflection is equal to the angle of incidence on glass, still water and polished
metal.

7.  When the reflected light reaches your eyes you see an image.
 There are two kindsof imagesthatcan beformed with light: real images and virtual images.
 Real images are images such as those produced on a cinema screen by biconvex lenses.
 Virtual imagescannotbeprojected onto a surfacebutonly appearto exist, such as thosein a
plane mirror or other smooth, shiny surface.
 The virtualimage of yourself is thesamesize asyou are,and is at the samedistancefromthe
mirror’s surface as you are but behind the mirror instead in front of it.
 Your imagein the mirror is the wrong way around,because you’releftshoulderwill appearto
be your right shoulder.
 Two planemirrors may beused to give a person atthebackof a crowd a view of an event.This
device is called a periscope.
 Most objects have rough surfaces.
 When light rays strike any rough surfaces the rays are scattered in different directions.
Passing light through transparent materials:
 If a ray of light is shone on a still glass block, the light ray will pass straight through.
 If a ray of light is shone on a tilted glass block, the light ray will refract.
 Refraction is the bending of the light ray.
 Light is refracted if the incident ray is not at 90° to the surface of the transparent material.
 A rainbow is produced by the refraction and reflection of the Sun’s light through the water
drops
 If all the colorsare reflected the objectappearswhite;if all the colors are absorbed theobject
appears black.
 Most objects absorb some colors and reflect others.
 2. Light travels much faster than sound. For example:
 Thunder and lightning start at the same time, but we will see the lightning first.
 When a starting pistol is fired we see the smoke first and then hear the bang.
 Shadows are places where light is “blocked”:
 Smooth, shiny surfaces have a regular reflection
 Rough, dull surfaces have a diffuse reflection.
 Diffuse reflection is when light is scattered in different directions
 Two types of reflection, regular and diffuse
 Mirrors come in 3 types: plane, convex and concave. Each has a distinct shape and use.
 Mirrors can make virtual images or real images depending on their type
 Virtual images - light rays do not meet and the image is always upright or right-side-up
 Real images - always upside down and are formed when light rays actually meet

8.  Plane mirrors are flat and make “virtual images”. The images is “virtual” because the light
rays do not come from the image, they only appear to
 Concave Mirrors are curved inward - just remember, you go “in” to a cave, and “in” to a
concave mirror!
 Convex mirrors are mirrors that curve outward
 Convex mirrors are used for security purposes,in cars etc. They allow us to see a wide view.
The images they make are virtual
Refraction
• Refraction is when waves speed up or slow down due to travelling in a different medium
• A medium is something that light waves will travel through
• Light rays are slowed down by the water
• Causes the ruler to look bent at the surface
• The mediums in this example are water and air.
• The degree that light bends when it enters a new medium is called the “index of refraction”
• Light rays slow down when they enter a new medium
• Refraction can cause light rays to change their direction
• All transparent materials have their own “index of refraction”
• Light is refracted when it passes through lenses and this creates images
White light can be split up to make separate colours. These colours can be added together
again
The Dual Nature of Light
1. Light as a wave
2. Light as a particle
The WAVETheory of Light:Thetheory thatlightsis transmitted via waveformwasproposed by
Christian Huygens in 1679. According to the theory:
 light corpuscles have mass and travel at extremely high speeds in straight lines
 rectilinear propagation - blocked by large objects (well-defined shadows)
 obey the law of reflection when bounced off a surface
 speed up when they enter denser media
 paths in denser media "bend towards the normal"
 prism dispersion - contradicted corpuscular theory
The Particle Theory of Light: The theory that light is transmitted via corpus car form was
supported and advocated by Sir Isaac Newton. According to his theory:
• waveletenvelop model(each point on a wavefront acts as a source for the next wave front)
• plane waves generate plane waves, circular waves generate circular waves

9. • light was composed of longitudinal waves like sound
• obey the law of reflection when bounced off a surface
• wavesslowed downwhen they entereda densermediumcausing theirpathsto "bend towards
the normal"
• light SHOULD produce interference patterns and diffraction patterns
 The electromagnetic spectrum is the range of all possible frequencies
of electromagnetic radiation. Electromagnetic waves are formed when an electric
field couples with a magnetic field. It is a continuum of all electromagnetic waves
arranged according to frequency, wavelength and energy.
 Wavelength is inversely proportional to the wave frequency
 Photon energy is directly proportional to the wave frequency
 λ = E / f
Radio waves:
• Have the longest wavelengths but least energetic
• Utilized by antennas
• They are used for transmission of data, via modulation.
• Television, mobile phones, wireless networking, and amateur radio all use radio waves.
Microwaves:
• Very easily absorbed by water
• Cause water and fat molecules to vibrate, which makes the substances hot.
• Good for transmitting information because microwave energy can penetrate haze, light rain
and snow, clouds, and smoke.
• Mobile phones, fixed traffic speed cameras, and radar, which is used by aircraft, ships and
weather forecasters, all use microwaves.
Infrared Radiation: Can be detected by special infra-red film.
• Primary source of infrared radiation is heat or thermal radiation
• Our skin emits infrared light, which is why we can be seen in the darkby someoneusing night
vision goggles.
• Ex. remote control
Light: Visible light waves are the only electromagnetic waves we can see. We see these waves as
the colors of the rainbow.
UV rays:
• Main natural source is the sun and other stars
• Can break chemical bonds, making molecules unusually reactive
• Often harmful to plants and animals, including humans

10. • Used to kill microbes, getting a sun tan, detecting forged bank notes
X-rays:
• Also called as Roentgen rays in honour of their discoverer
• Given off by stars and are strongly emitted by some types of nebulae.
• Have so much energy and such a short wavelength that they can go right through you
• Used by doctors to see inside people
Gamma Rays:
• Shortest-wavelength, Highest energy
• Mostdangerousand mostpenetratingof allelectromagneticradiation,and arequite difficult
to stop
• Result of violent cosmic eventssuch as supernovas,othernuclearexplosions,and radioactive
decay
• Used to kill cancer cells ("Radiotherapy")
Light Sources:
Light is a form of energy. To create light, another form of energy must be supplied. There are two
common ways for this to occur, incandescence and luminescence.
Incandescence:"Black body radiation"
It is the emission of light from a hot body as a result of its temperature.
Involves the vibration of entire atoms
Sunlight, regular light bulbs (not florescent) and fires are all incandescent sources of light.
"Cold light"
Itis theemission of lightby a substancenotresulting fromheat.Itcan becaused by chemicalreactions,
electrical energy, subatomic motions, or stress on a crystal.
Involves only the vibration of electrons
Ex. computer monitors, televisions, and florescent lights, fireflies
Luminous and Illuminated Bodies:
The objects that we see can be placed into one of two categories: luminous objects and illuminated
objects. Luminous objects are objects that generate their own light. Illuminated objects are objects
that are capable of reflecting light to our eyes.
A luminousbody,suchasthesun,anotherstar,ora lightbulb,isthusdistinguishedfroman illuminated
body,such asthemoonand mostof theotherobjectsonesees.Luminousobjectsgiveoff lightwhereas
illuminated objects reflectlight.Examplesof luminousbodiesarethesun,stars,fireflies,lighted candle,
light bulbs...
Illuminated bodies not only reflect light but sometimes also transmit it, such as the opaque,
transparent and translucent materials. An example of an illuminated body is the moon.

11. • TranslucentObjects:Thesekinds of objects scatter or disperse light when light falls on them.
• They are said to transmit light in the absence of details
• You can only see a blur image when you peek through these
• Frosted glass and waxed paper are examples of translucent objects.
• Transparent Objects: They are those that allow light to pass through readily.
• These kind of objects have absolute clarity.
• You can see right through them.
• The water, air and glass are all transparent objects.
Opaque Objects: These objects do not allow light to pass through.
• They absorb some of the light that is cast on them.
• Wood, paper and many more are examples of such objects.
Light : Electromagnetic ,transverse, travel very fast
Sound : Mechanical ,Longitudinal ,travel slower.
Radio waves are produced by charges accelerating in a wire
Microwaves are used in radar systems in air-traffic control, for transmitting long distance phone
communications in outer space, and to cook food
Infrared waves appear as heat when absorbed by objects
The speed of light in a material is always less than c
v=fλ applies to light waves
Light travels so fast.From yourlesson last year,it is approximated to travelat a speed of 3 x 108 m/s
in a vacuum.Thisspeed decreaseswhen lighttravelsin a densemedium.Thismeansthatthespeed of
light is dependenton the propertiesof the medium.In the case of light, it is dependenton the optical
densityof themedium.Theopticaldensity of themediumisdifferentfromitsphysicaldensity.Physical
densityis described as the massper unit volumeof the medium.On the other hand,the sluggishness
of theatomsof a mediumto maintain theabsorbed energybeforereemitting itiscalled opticaldensity.
When light crosses the boundary of two media of different optical density, a change in speed takes
place. This change in speed is manifested as bending of the light ray.
Known indices of refraction:

12. The index of refraction of a material is a quantity thatcomparesthe speed of light in that material to
its speed in a vacuum.Sincethespeed of lightin vacuumisthehighestattainablespeed in theuniverse,
the index of refraction is always greater than 1. The n values of other media are shown in Table 1.
Again, dispersion is a special kind of refraction which provided us colors of light. This phenomenon is
observed when white light passes through a triangular prism. When white light enters a prism,
separation into differentcolor is observed.Remembertheconceptof refractiveindices in the previous
moduleand in thefirst partof the lesson?The refractiveindices of the differentcolorsof light indicate
that light of different colors travels at different speeds in the prism which accounts for the different
degrees of bending. Thus, blue light with greater refractive index refracts more and appears at the
bottom of the red light.
All of these objects can be seen in the dark because they let out their own light-they are luminous