PHYSICS – LIGHT AND GEOMETRIC OPTICS

Light and Colour

White light is actually composed of a combination of many colours - all the colours of the rainbow.

If a second prism is added the colours can be recombined to produce white light. This proves that white light is made up of multiple colours

The Electromagnetic Spectrum

Additive Colour Theory of Light These three colours of light are

known as primary colours.

Additive Colour Theory of Light

If you mix correct amounts of all three primary colours of light, you will make white light. If you mix only two of the primary colours together, you will make a secondary colour.

The secondary colours of light for red, green, and blue are magenta, yellow, and cyan.

Subtractive Colour Theory of Light

When a light wave strikes an object Some wavelengths of light reflect,

which means that they bounce off the object.

Other wavelengths are absorbed by the object.

The colour you see when you look at an object depends on the wavelengths that are reflected

Subtractive Colour Theory of Light

The primary and secondary colours of light for the subtractive theory are opposite to the colours of the additive theory

Cyan, magenta, and yellow are the primary subtractive colours, while red, green, and blue are the secondary subtractive colours.

Producing Visible Light

The most important natural source of light on Earth is the Sun. There are, however, other natural sources of light, such as light from other stars, fire, and lightning. Light is also produced by other methods

Bioluminescence

The ability of a plant or animal to produce light is called

90 percent of all sea creatures are bioluminescent

Some fish produce their own light, while others have bacteria that carry out the light-producing chemical reaction for them.

Incandescent Light Produced by an

object, such as a metal, that is at a very high temperature.

Inside an incandescent light bulb is a filament Electric current flows

through the filament, heating it to an extremely high temperature.

Fluorescent Light

Light emitted by substances when they are exposed to electromagnetic radiation.

A fluorescent light bulb is a glass tube filled with a small amount of a gas such as mercury vapour. The inside of the bulb is coated with a white powder called a phosphor.

Phosphorescent Light

In fluorescent lights, the phosphor emits light only while it is exposed to ultraviolet radiation.

Some substances have the ability to store energy from radiation.

Chemiluminescence

Light produced from a chemical reaction without a rise in temperature.

All forms of bioluminescence are special kinds of chemiluminescence.

Example: Glow sticks

Triboluminescence

Producing light from friction Some crystals can be made to glow

simply by rubbing them together or crushing them.

Electric Discharge

The process of producing light by passing an electric current through a gas

Example: Neon lights, Lightning, Carbon arcs, HIDs

Light-Emitting Diode (LED) The process of transforming

electrical energy directly into light energy is called electroluminescence.

A light-emitting diode (LED) is an electroluminescent light source made out of a material called a semiconductor.

Light and Matter Ray diagrams are used to describe

what happens when light strikes an object.

Light travels in straight lines until it strikes something.

Material have different properties which affects what happens when light strikes them

A ray diagram demonstrating the law of reflection Normal – Dashed line drawn

perpendicular to the mirror at point of reflection.

Incident Ray – The Incoming Ray of light

Reflected Ray – The outgoing Ray of light

Law of Reflection

When light reflects off a surface, the angle of incidence is always equal to the angle of reflection.

Plane Mirror drawings

Images are always drawn in dotted lines

the point at which the extended reflected rays converge (come together) behind the mirror indicates the size and distance of the object

Drawing a Concave Mirror Ray Diagram

1. Use an upright arrow to represent the object

2. Show real rays as solid lines. 3. Use dashed lines to present

virtual rays, which are rays that only appear to exist behind the mirror.

S = Larger A = Upright L = Behind Mirror T = Virtual

Images formed by Concave Mirrors- Image in front of F

STEP 1STEP 2STEP 3

Concave Mirror – Image behind CSTEP 1STEP 2STEP 3

S. Smaller than object

A. Inverted

L. In front of mirror

T. Real

Summary of Images in a Concave Mirror

Drawing a Convex Mirror Ray DiagramSteps

1. Draw a line from the top of the object straight across (parallel to the principle axis) to the mirror. Then draw a dotted line from there to the focal point. This line is also drawn as a solid line on the outside of mirror as it moves away from the mirror surface.

2. Draw a line from the top of the object to the center of curvature. Once the line reaches the mirror it becomes dotted.

3. Draw a line from the top of the object to the vertex. The reflected ray will leave the mirror at the same angle as the incident ray angle. Extend the reflected ray as a dotted line behind the mirror

The point at which all the lines meet is where the top of the virtual image is located.

Images formed by Convex Mirrors

STEP 1STEP 2 STEP 3

S = Smaller A = Upright L = Behind Mirror T = Virtual

Refraction

The bending of light rays as they pass between two different media is called refraction Refraction is used in designing and

building lenses The bending of light is due to

different media slowing light down by different amounts. The more light slows down the more it is refracted.

The Index of Refraction

The amount by which a transparent medium decreases the speed of light is indicated by a number called the index of refraction, also called the refractive index.

The larger the refractive index, the more the medium decreases the speed of light.

The Index of Refraction

Since units cancel, a refractive index value does not have any units.

Index of refraction of Material = Speed of light in vacuum Speed of light in medium

OR

n = c v

Dispersion

The refraction of white light into separate wavelengths, or colours.

A diamond can appear completely colourless and yet glitter in all colours of the rainbow because the amount of refraction is different for each colour.

Snell’s Law

Snell’s law is a formula that uses values for the index of refraction to calculate the new angle that a ray will take as a beam of light strikes the interface between two media.

Snell’s Law

If you call the indices of refraction of the two media n1 and n2 and call the angles of incidence and the angle of refraction θ1 and θ2, then the formula for Snell’s law is:

n1sinθ1 = n2sinθ2

Total Internal Reflection

In total internal reflection, light reflects completely off the inside wall of a denser medium (higher index of refraction) rather than passing through the wall into a less dense medium (lower index of refraction).

Mirages

Since the light rays pass through layers of air with progressively lower indices of refraction, eventually the light is totally internally reflected.

Concave Lenses A diverging lens is

sometimes called a concave lens because it is thinner in the centre than at the edges.

As parallel light rays pass through a concave lens, they are refracted away from the principal axis.

The light rays diverge and they will never meet on the other side of the lens.

The image formed is always upright, virtual and smaller than the object

Drawing a Concave Lens Ray Diagram Any two of the following rays may be

used to locate the image:1. Draw a ray parallel to the principal

axis that is refracted through the principal focus (F).

2. Draw a ray that passes through the secondary principal focus (F') and refracts parallel to the principal axis.

3. A ray that passes through the optical center goes straight through, without bending.

Only two of these lines are needed to find the image

Drawing a Concave Lens Ray Diagram

S: Smaller A: Upright L: In front of F T: Virtual

2F F F’’ 2F’

Convex Lenses

A converging lens is also called a convex lens because it is thicker at the centre than at the edges.

As parallel light rays travel through a convex lens, they are refracted toward the principal axis.

This causes the rays to move toward each other. The light rays cross at the focal point of the lens.

Converging lenses are often used as magnifying glasses

Drawing a Convex Lens Ray Diagram1. Any ray that is parallel to the

principal axis is refracted through the principal focus (F).

2. A ray that passes through the secondary principal focus (F') is refracted parallel to the principal axis.

3. A ray that passes through the optical center goes straight through, without bending

As with converging mirrors, only two rays are required to locate an image. The third one acts as a check

Object between 2F’ and F’

S: Larger A: Inverted L: Behind 2F T: Real

2F’ F’ F 2F

Convex Lenses

Thin Lens Equation

The distance of the object from the lens, do, the distance of the image from the lens, di, and the focal length of a lens, f , can all be related using the thin lens equation. Given any two of these quantities, you can use the thin lens equation to solve for the third:

1 = 1 + 1

ƒ do di

Human Vision

The outer surface of your eye where light enters is made of a transparent layer of tissue called the cornea.

Light can pass right through the cornea yet it is tough enough to protect the inner eye.

Far-Sightedness

The eye cannot make the lens thick enough to refract diverging light rays from nearby objects correctly on the retina.

Instead, the image falls into focus behind the eye, resulting in a blurry image on the retina.

A converging lens in front of the eye helps the light rays form the image correctly on the retina

Near-Sightedness

Distant objects are refracted so much that the image forms in front of the retina instead of on it.

The eye cannot make the lens thin enough, resulting in a blurry image.

A diverging lens placed in front of the eye helps the lights rays form the image correctly on the retina.

Astigmatism

A condition where the eye is unable to form a clear image because of an irregular shape of the cornea or lens. This causes an image to be formed on more than one place on the retina, which results in blurry vision.

Types of Telescopes

There are two main types of telescopes: refracting telescopes and reflecting telescopes.

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Types of Telescopes

Refracting Telescopes A refracting telescope

is similar in design to a microscope, in that they both have two lenses, one on each end of a long tube.

Cameras

A camera is a lightproof box with a lens at one end to form a real, inverted image on a light detector or light-sensitive plate or film.

For a distant object, the image distance di is equal to the focal length of the lens. For nearer objects, the lens must be moved farther from the light detector so that the image is still focussed.

Lasers

A laser is an optical device that produces a form of light in which all the light rays are almost perfectly parallel, all have the same wavelength, and all of the wave crests and troughs are exactly lined up.

CLIMATE

Weather and Climate

Although weather and climate are related, they are not the same thing.

Weather - refers specifically to the environmental conditions that occur at a particular place at a particular time.

Temperature, air pressure, cloud cover, and precipitation.

The effects of weather are immediate and obvious.

Weather and Climate

Climate - is the average weather conditions that occur in a region over a long period of time, usually a minimum of 30 years.

Average monthly temperatures and precipitation, average wind speed and direction, and a variety of other data.

Climate is studied by climatologists

Earth’s Biosphere

Earth may be divided into four spheres Biosphere (bio = living, Sphere =

ball) ; The living layer around the planet

Includes – atmosphere, lithosphere, and hydrosphere

Earth’s Biosphere

Atmosphere (atmos = gas) ; The gas layer around the planet

Lithosphere (lithos = rock); The rock layer around the planet

Hydrosphere (hydro = water); The water layer around the planet

Atmosphere Air is the mixture of different gases

found in the Earth’s atmosphere. The layer of gas that extends out 300km

from the Earth’s surface. Major gasses – Oxygen and Nitrogen

Trace Gases – Argon, carbon dioxide, helium, methane, and krypton

Layers in the Atmosphere

Earth’s Biomes

A biome is a large geographical region with a defined range of temperature and precipitation - its climate.

Each biome is characterized by the plants and animals that are adapted to that climate.

The Earth has 11 different terrestrial biomes. ◦ The oceans are the marine biome which

about 70 percent of Earth.

Trapping Heat

Some of the solar radiation heats the objects in the greenhouse which then heat the air.

The warm air cannot escape the glass.

Insolation and the Natural Greenhouse Effect

Different areas on Earth receive different amounts of solar radiation.

Insolation - the amount of solar radiation received by a region of Earth’s surface.

Insolation depends on latitude, which is the distance of any place on Earth from the equator, shown on a globe by a series of lines drawn around it parallel to the equator.

The Natural Greenhouse Effect

The absorption of thermal energy by the atmosphere is known as the natural greenhouse effect.

This helps keep the temperature of our planet in the range that supports life.

Water vapour, carbon dioxide, nitrous oxide, and methane are called greenhouse gases, gases that contribute to the natural greenhouse effect. Since so much water vapour is present in the atmosphere, it is the main contributor to the natural greenhouse effect.

The Net Radiation Budget

Almost all the energy absorbed by Earth’s atmosphere, lithosphere, and hydrosphere is eventually radiated back into space as infrared radiation (heat)

Less than one percent of the incoming solar radiation is transformed by photosynthesis into chemical energy.

Albedo

The albedo of a surface is the percent of the incoming solar radiation that it reflects.

Light-coloured, shiny surfaces like snow, ice, and sand reflect much more solar radiation, 90%

Darker, duller surfaces such as open water (about 10 percent), forests, and soils.

Albedo varies with the seasons and can affect a region’s radiation budget because it can affect the temperature and rate of evaporation in that region.

Thermal Energy Transfer

The movement of thermal energy from an area of high temperature to an area of low temperature.

Thermal energy transfer can occur by radiation, conduction, or convection.

Radiation

Radiation - the emission of energy as waves. When radiant energy encounters particles of matter, it may be reflected or absorbed. Absorbed energy increases the motion of particles.

An increase in kinetic energy increases the temperature of the matter.

Any substance at a higher temperature than its surroundings will emit radiant energy, usually as infrared radiation. The warmed matter then transfers some of its thermal energy to substances at lower temperatures or re-emits it as infrared radiation.

Conduction

Conduction - The transfer of thermal energy through direct contact between the particles of a substance, without moving the particles to a new location. Thermal energy transfer by conduction usually takes place in solids. During conduction, particles with more kinetic energy transfer some of their energy to neighbouring particles with lower kinetic energy increases the kinetic energy of the neighbouring particles.

The Coriolis Effect

The air currents from the equators and poles would move directly North and South but since the Earth is rotating on its axis, the winds are deflected either toward the right or toward the left. The Coriolis effect is the deflection of any object from a straight-line path by the rotation of Earth. The Coriolis effect causes moving air or wind to turn right in the northern hemisphere and left in the southern hemisphere.

Convection

- The transfer of thermal energy through the movement of particles from one location to another. Thermal energy transfer by convection usually occurs in gases and liquids. During convection, the movement of the particles forms a current, which is a flow, from one place to another in one direction. Liquid water has a high heat capacity which means that it takes a lot of energy to increase the temperature of a mass of water. Since Earth’s surface is over 70 percent water, water has a large effect on Earth’s climate. Therefore, regions closer to large bodies of water tend to experience more moderate weather conditions than regions farther from them.

Global Wind Patterns

Jet Streams

Local conditions such as the presence of continents or large bodies of water also affect wind patterns.

A jet stream is a band of fast-moving air in the stratosphere. Because of their high altitude, these winds are not subject to much friction and so are much faster than winds closer to Earth’s surface.

Thermal Energy Transfer in the Oceans

Greenhouse Gases

Gas Global Warming Potential over 100

years

Persistence (Years)

Carbon Dioxide CO2

1 -

Methane CH4 25 12

Nitrous Oxide N2O

298 114

Greenhouse Gas Concentrations

The additional greenhouse gas emissions are causing the anthropogenic greenhouse effect, which is the enhancement of the natural greenhouse effect due to human activities.

Greenhouse GasesGreenhouse Gases

Sources

Carbon dioxide CO2

- Burning coal, oil, gasoline, and natural gas

- Cement making

- Deforestation

Methane CH4 - Production of petroleum products

- Rice paddies, landfills, cattle

- Natural gas leaks

- Coal mining

Nitrous Oxide N2O

- Burning coal, oil, gasoline, and natural gas

- Fertilizer

Increasing Greenhouse Gas Emissions

Human Activities Contribute to Climate Change

The Pasterze, Austria's longest glacier

Portage Glacier

Mt. Hood Oregon

Mt. Hood Oregon

Physical Effects of climate change

In Canada’s north, areas of permafrost (permanently frozen soil) are thawing much more in the summer than they used to. As a result, the soil becomes looser.

Trees that tilt or fall over because of this are called drunken trees

Drought

Droughts are most severe when they affect regions near deserts. Until recently, many of these regions had seasonal rains that provided the water needed to grow crops and keep animals.

Wildfires

When the weather is hot and dry for a long time, the trees may become so dry that they lose their leaves. The probability of wildfires increases.

While the frequency of wildfires is low around the world compared with other natural disasters such as drought, it is increasing.

Storms

Changes in the frequency and severity of storms are one potential effect of the rapid increase in average global temperature and the movement of energy throughout the world

Floods

When the air temperature warms rapidly in spring, the snow can melt too quickly for the rivers and streams to handle the run-off.

These “seasonal” floods damage homes and cropland and are becoming more frequent.

Melting Ice

In the Arctic Ocean, the amount of sea ice in the summer has decreased substantially. The average level of the world’s oceans has increased by about 20 cm over the past century. This is caused by land glaciers melting and water expanding as it warms.

Ocean Warming

As the water warms, it expands, so warmer oceans mean higher sea levels, loss of coastal land.

Warmer water absorbs less carbon dioxide (just as cold pop retains more carbon dioxide than warm pop does), so it is less effective as a carbon sink.

Ocean Currents

Oceans act as Earth’s heating and cooling circulation system. As the temperature of Arctic water increases, it can lead to more extreme weather around the planet.

Effects of Climate Change on Wildlife

Polar bears normally walk on the ice to hunt seals, because seals swim too quickly for the bears to catch them in open water.

However, when the seals come up to a hole in the ice to breathe, the bears can capture them. Less ice means poorer hunting, and polar bears are going hungry.

Range Shifts

Ticks and other pests are also moving North as the climate warms.

Wildflowers are blooming 26 days earlier now.

Organisms That Benefit from Climate Change

Some organisms may find their environments improved as the climate changes.

Several species of free-living jellyfish have increased up to 100 times in many coastal areas of the oceans.

GOOD LUCK ON YOUR FINALStudy Hard