Light and Geometric Optics UNIT THREE Bohr – atom: https://www.youtube.com/watch?v=-YYBCNQnYNM  Light and Geometric Optics

Big Ideas Light has characteristics and properties that can be manipulated with mirrors and lenses for a range of uses Society has benefited from the development of a range of optical devices and technologies.

E LOOKING AHEAD UNIT UNIT C Light and Geometric Optics CHAPTER 10 The Production and Reflection of Light CHAPTER 11 The Refraction of Light CHAPTER 12 Lenses and Optical Devices

Chapter 10: The Production & Reflection of Light What is Light? Chapter 10: The Production & Reflection of Light

Learning Goal Light is …. To understand the characteristics of light: The sources and nature of light Necessary A Wave FAST Made up of different Colours Source of Energy Useful! Travels through Space

Light is Necessary We use light to keep us warm We use light to illuminate things and help us see We use light to give us food plants need light, herbivores starve from no plants, carnivores run out of animals to eat because herbivores arent reproducing

Light is FAST! Light travels at VERY High Speeds (299 792 458 m/s = the speed of light) Light travels soooo fast that something travelling at the speed of light could circle the Earth about 7.5 times in just one second! When you turn on a light switch, it seems instant and a room is filled with light

Light is a Source of Energy Light energy comes from many different sources, both natural and artificial Natural: The Sun = VIP source of natural light Artificial: objects created by people

Light travels through SPACE Light is a form of energy that can be transmitted without a medium (any physical substance that acts as a carrier for the transmission of energy – like boiling water) BUT light travels through the vacuum of outer space This means that light does not require a medium for transmission of its energy. Instead, light energy is transferred through radiation 1. conduction: transfer of heat from one point to another point in a material (ex. steel rod) where there will not be any physical movement involved in the material.  2. convection: transfer of heat from one point to another through a mediaum (ex. water boiling from the vessel bottom to top)  3. radiation: transfer of heat through vacuum.( ex heat from SUN to Earch) radiation a method of energy transfer that does not require a medium; the energy travels at the speed of light

Light is a WAVE ~ In the1800’s, Thomas Young discovered how light demonstrates wave-like properties, which James Clerk Maxwell later called electromagnetic waves These electromagnetic waves have both electric and magnetic parts, are transferred by radiation, and travel at the speed of light

Low-energy: Radio Waves or High-energy: X-Rays Light is a WAVE ~ Later scientist were able to prove the existence of these electromagnetic waves which can be Low-energy: Radio Waves or High-energy: X-Rays Scientists classify electromagnetic waves based on energy the waves have. This classification system is called the electromagnetic spectrum

Light is a Made up of different colours Referring to the Electromagnetic Spectrum: Visible light is any electromagnetic wave that can be seen by the human eye (also referred to as White Light) It only represents one small part of the electromagnetic spectrum

Light is a Made up of different colours Visible light (WHITE LIGHT) is made up of 7 different colours of light: Red Orange Yellow Green Blue Indigo Violet (ROYGBIV) Each colour in the visible spectrum has a different amount of energy visible spectrum = the continuous sequence of colours that make up white light Red: has LOW frequency and LONG Wavelengths Violet: has HIGH frequency and SHORT Wavelengths

Light is Useful Electromagnetic waves have many uses in society:

Sources & Nature of Light

Types of light emissions There are many sources of light Some are Natural (like the Sun) Some are Artificial (like a light bulb) However, notice how both these types of light also produce heat Any light that is given from a hot object is called “white light” Where it is actually NOT WHITE but in fact many different colours all together

Types of light emissions Light can also be emitted from sources that are not hot, such as fireflies and fish All light sources, regardless if natural or artificial: Atoms within the materials MUST ABSORB ENERGY After absorbing energy, we see how these atoms will then be in an “excited state” These atoms can’t be “excited” forever, and quickly release their energy This release of energy is seen as LIGHT

Light from the sun The largest source of light to man is THE SUN A huge amount of energy is released when hydrogen atoms in the sun’s core collide or come together (making Helium) through fusion reactions When these atoms collide, a lot of energy is released from the sun

Light from incandescence When you look at a traditional light bulb – you witness incandescence lighting An incandescent light bulb is made up of tungsten wire and releases light by: Having electricity flow through the tungsten wire The wire then heats up And light is emitted in the process This is because the electrical energy that flows through the wire excites the tungsten atoms = light It also emits infrared light that you feel as heat radiating from the bulb

Light from incandescence While you may feel heat given off from an incandescent light bulb in your room, this is not a good measure of how effective this light source is In fact it sucks! Only about 5% of the electricity used in an incandescent light bulb turns into light The other 95% is lost as heat This is one of the main reasons why people are choosing to replace old incandescent light bulbs with more efficient light bulbs based on newer technology

Light from electric discharge Every time you see a flash of lightning or walk past a lit neon sign for a business, you are seeing light being produced through electric discharge This occurs when an electric current passing through a gas The electricity causes the gas to glow

Did you know …

Light from electric discharge Although the term “neon lighting” is usually used to describe all signs that use this process, many gases other than neon can be used For example: Neon gas produces the familiar red colour, helium produces a gold-coloured glow, argon a pale violet-blue, and krypton a greyish off -white.

Light from Phosphorescence Objects that glow in the dark, like dials on some wristwatches and clocks, and glow-in-the-dark stickers. These glow-in-the-dark materials are coated with phosphors materials that give off light through a process called phosphorescence Phosphors absorb light energy, particularly ultraviolet light

Light from Phosphorescence These materials hold onto some of the energy for different amounts of time (depending on the material), and release visible light at a lower energy Because light is emitted over a period of time, phosphorescent materials are often described as “glow-in-the-dark”

Light from Fluorescence Fluorescence occurs when an object absorbs ultraviolet light and immediately releases the energy as visible light

Light from Fluorescence A fluorescent light makes use of both electric discharge and fluorescence A fluorescent light tube is filled with very low-pressure mercury (Hg) vapour The inner surface of the tube is also coated with a fluorescent material When a fluorescent light is turned on, the electric current causes the mercury atoms to emit ultraviolet light This ultraviolet light then strikes the fluorescent inner surface of the tube, resulting in the production of visible light

Light from Fluorescence

Light from Fluorescence Fluorescent lights are 4 – 5 x more energy efficient than incandescent light bulbs A fluorescent light can provide the same light output as the same incandescent bulb, but produces much less heat and uses much less electricity Compact fluorescent lights (CFLs) are recommended more since they use less energy to operate

Light from Chemiluminescence Have you ever played with a light stick or a glow stick? Have you ever worn a necklace or bracelet at a concert or fair that, when bent and shaken, gave off visible light? If so, then you have seen light produced by chemiluminescence

Light from Chemiluminescence Chemiluminescence is the production of light as a direct by-product of a chemical reaction Almost no heat is produced as a result of this type of reaction This is why this type of light is often called “cold light”

Light from Chemiluminescence Light sticks operate by causing two chemicals to mix. The chemicals are originally separate in the light stick. One chemical is in a narrow, small glass vial in the middle of the stick; the second chemical is in the main body of the stick. Bending the light stick in the middle causes the small glass vial to break, This allows the two chemicals to mix in the main body of the stick. The chemical reaction that occurs produces visible light.

Light from Chemiluminescence Benefits Light sticks are inexpensive to manufacture Light sticks are very durable. Light sticks do not require an electric current, so they are useful in hazardous environments where a spark could be quite dangerous.

Light from Bioluminescence When chemiluminescence occurs in living organisms, scientists call it bioluminescence. Is the production of light in living organisms as the result of a chemical reaction with little or no heat produced Bioluminescence occurs in a wide variety of organisms, including certain bacteria, fungi, jellyfish, fish, and the well known examples of glow-worms and fireflies

Light from Triboluminescence Triboluminescence is the production of light from friction when certain crystals are scratched, crushed, or rubbed against one another Unlike other methods of producing light, triboluminescence does not really have any practical application at this time https://www.youtube.com/watch?v=hPtCvReouCM

Light from a Light-Emitting Diode A light-emitting diode (LED) is a special electronic device that produces light when an electric current flows through it in only one direction This happens by using special materials called semiconductors Unlike a conductor, that allows current to flow in either direction, semiconductors only allow electric current to flow in one direction

Light from a Light-Emitting Diode An LED is different than an incandescent bulb, where: it does not require a filament it does not produce much heat as a by-product it is more energy efficient If one section goes out, the whole line doesn’t Improvements in LED technology have them being used in many areas, such as Christmas lights, illuminated signs, and traffic lights.

Checking for understanding   LEDs are considered an even better alternative to CFLs to  replace incandescent bulbs. Compare CFLs with LEDs.  Are LEDs a better alternative? Be sure to consider environmental, health, and economic factors. Write a brief report to communicate your opinion