Grade 10 Science Exam Study Note Chemistry – Pg1, Biology – Pg11, Optics/Light – Pg 20 Chemistry Physical and chemical properties and changes •Physical Properties: Something you can see or observe with your senses oState oColour oSize oLuster/Shinyness oSmell oMelting/Boiling Points oSolubility oViscosity oDensity •Chemical Properties: Characteristics used in a chemical reaction oTendency to React oCombustibility oTendency to Rust •Physical Changes oEasily reversible oDoesn’t change the substance oOnly changes physical properties •Chemical Changes oCreates new substance oUsually irreversible Can change physical properties in addition to changing chemical ones Evidence of chemical changes: •Change in colour •Heat or light produced •Production of gas bubbles •Precipitate formed •Change in smell Patterns and the Periodic Table oPeriods: The rows of the table that refer to the number of orbits oGroups: The columns of the table that indicate the number of valence electrons ? 1st Group Alkaline Metals: Very reactive due to having only 1 valence electron (Lithium, Potassium) ? 2nd Group Alkali Earth Metals: Quite reactive due to only having 2 valence electrons (Calcium, Magnesium) ? -6 Group Metalloids: Semi reactive, have traits of both metals and non metals (silicon, boron) ? 4-6 Group Other Non-Metals: Broad characteristics, can create molecular compounds (Oxygen, nitrogen, carbon) ? 7th Group Halogens: Very reactive due to having only 1 less than a full shell (Flourine, Chlorine) ? 8th Group Noble Gases: Not reactive due to having a full shell (Argon, Neon, Helium) oCations are Positive Ions oAnions are Negative Ions •Lewis dot diagrams •Electron arrangements and reactivity.
Explain why alkali metals are highly reactive. Electrons are arranged into shells as are shown in the Bohr-Rutherford diagrams right. Lithium (Li-7) has only one electron in it’s outermost shell (one valence electron) which makes it very prone to reactions because it only needs to lose one electron to become stable and have a full outer shell. Similar is Fluorine (F-19) which only needs to gain one to become stable. Both Alkali Metals (group that Lithium is in) and Halogens (group that Fluorine is in) are highly reactive due to their having only 1 valence electron, or 1 less than a full outer shell respectively. Ionic compounds and their properties oPropetieis: Always have one metal and one non-metal. The metal is said first and then the non-metal with –ide on the end. They also have very strong bonds and many are electrolytes which mean when dissolved in water, they conduct electricity. Pure water is a bad conductor of electricity but tap water, lake water, ocean water, and pool water are very good conductors because they contain many dissolved ions. Therefore it is very important to stay out of the water during lightning storms. oE. x. NaCl Sodium Chloride. (Table Salt) oNaming ionic compounds o o Writing chemical formulas of ionic compounds When writing chemical formulas for ionic compounds remember that the charge of the new compound must be zero. Therefore an easy way to ensure this is to use the “crisscross” method as is seen below. Just remember to reduce to smallest terms if possible. (i. e. 2,2 -> 1,1) oElements with multiple ionic charge: Some Metals have multiple charge possibilities and therefore must be specified when writing them in an equation or in any form. o o o o oPolyatomic ions: These are ionic compounds that instead of a single non-metal as the second ion, have a polyatomic ion.
Remember that polyatomics are one unit and can’t be separated in reactions. •Molecules and Covalent Bonding oCovalent bond, molecules and diatomic molecules ?Covalent Bond: A bond that results from the sharing of outer electrons between non-metals atoms ? Molecule: A particle in which atoms are joined by covalent bonds ? Diatomic Molecule: A molecule consisting of only two atoms of either the same or different elements. oProperties of molecular compounds ?Two non-metals ?Electrons shared oLewis structures and covalent bonding oWriting chemical formulas of molecular compounds Naming Molecular Compounds ?Common Molecular Compounds ?Prefixes are used to tell how many atoms there are for each molecule. “Dinitrogen Pentaoxide” tells that there are 2 nitrogen atoms and 5 oxygen atoms. If there is only one atom for the first part of the compound it doesn’t need the prefix “mono” but the second one does. From 1-8 here are the prefixes: Mono, Di, Tri, Tetra, Penta, Hexa, Hepta, Octa. Remember when asked to write compounds check if there is a metal, if it is then it is an ionic compound not molecular and should be named accordingly. REMEMBER -CH4: Methane -NH3: Ammonia NH4: Ammonium -NO: Nitric Oxide -H¬2S: Hydrogen Sulfide -Fossil Fuels are Molecular Compounds •Chemical Reactions oWord and skeleton equations oPhysical state symbols (s) (l) (g) (aq) are needed for skeleton equations to indicate the physical state at room temperature. In a skeleton equation numbers indicating the number of atoms are not needed.
Numbers indicating the number of each atom are needed for complete chemical equations as well as physical state symbols oBalanced chemical equations (reactants must equal products) oChemical reactions and the Law of Conservation of mass Mass cannot be destroyed or created, but only changed state ? Therefore there must be the exact same number of atoms on each side of the equation because the Law of Conservation of Mass cannot be broken oSolving problems using the law of conservation of mass •Types of Chemical Reactions (Letters below represent two different elements or compounds and the changes they go through in the chemical reaction) oSynthesis: A+B=AB oDecomposition AB=A+B oSingle displacement AB+C=AC+B oDouble displacement AB+CD=AC+BD oCombustion (complete and incomplete) CxHy+O2=H2O+CO2 x and y are variables because there are numerous hydrocarbons such as methane CH4 or octane C8H18 which follow the same chemical formula. x and y are just replaced with the numbers given. ?When indicating the number of CxHy, O2, H2O and CO2 put the number in front. Using these numbers may be needed to ensure a balanced equation E. x. CH4 + 2O2 = 2H2O + CO2 •Acids and Bases oPhysical and chemical properties of Acids oAcid: An aqueous solution (in water) that conducts electricity, tastes sour, turns blue litmus red, turns bromothymal blue yellow, neutralizes bases ?
Physical Properties •Taste sour •Conducts of Electricity •Acts as a preservative for many foods because harmful bacteria and microorganisms can’t survive in acid ? Chemical Properties •Reactive with metals and carbonates (baking soda) •Turns Blue Litmus red •Neutralizes bases •Always contain hydrogen ion ?Solutions can only conduct electricity if it contains ions. When acids are in solutions they break down to ions which make them conductive. Example: HCL(aq)=H+(aq)+Cl-(aq) oChemical formulas and names of acids (binary acids and oxyacids) oPhysical and chemical properties of bases Base: An aqueous solution (in water) that conducts electricity and turns red litmus blue, and phenolphthalein pink. ?Physical Properties •Taste bitter •Feel slippery •Conducts Electricity ?Chemical Properties •Changes colour of acid-base indicators •Always contains hydroxide ion oNames and chemical formulas of bases oThe pH scale and practical applications ?The pH scale is a measure of acidity from 0 to 14 with 0 being most acidic and 14 being least acidic. 7 is the middle with neutral amounts of acidity. ?Acidity in acids is determined by the number of hydrogen ions ?
Basicity is determined by the number of hydroxide ions ?pH solutions have very large effects on us, and our environment •pH of soil can vary a lot depending on many factors but certain plants and vegetables like beans and clover grow better in slightly basic (pH7-10) whereas corn thrives in mildly acidic soil (pH5-6). Potatoes prefer very acidic soil below pH5. pH of soil can also be changed through addition of compost or aluminum sulfate to increase acidity or mixing in of calcium oxide (lime) can decrease acidity. oNeutralization Reactions oApplications of neutralization reactions Acid precipitation, what it is and sources of acid-forming pollutants ? Precipitation (usually rain) that is excessively acidic (less than 5. 6 pH) due to increases of atmospheric Sulphur Oxides and Nitrogen Oxides creating Sulphuric Acid and Nitric Acid and then precipitating back to the earth oEnvironmental impact of acid precipitation ?Acid Rain can cause destruction to vegetation ?Also kill many aquatic creatures like fish and amphibians as well as the predators who feed on them ? Cause loss of nutrients from soil due to washing and dissolving away of metallic nutrients ? Loss of and weakening of forests Reducing acid precipitation ?Use of scrubbers on energy production plants and transportation vehicles which transform the sulphur dioxide and nitrogen oxides into sulphur and oxygen, and nitrogen and oxygen ? Biology 3 points of Cell Theory 1. All organisms are composed of one or more cells 2. The cell is the basic unit of live in all living cells 3. All cells are produced by the division of pre-existing cells Difference between prokaryotes(single cell organisms) and eukaryotes(single or multi-cell organisms) (pg 29) •Prokaryotes oNo nucleus oVery simple organisms ?Achaea and Bacteria Eukaryotes oContains a nucleus oAre much larger oMore complex organisms ?Protists, fungi, animals and plants Cell structure – organelle functions in plant and animal cells OrganelleFunction CytoplasmContains all the organelles, mostly water but contains some substances that are stored until the cell needs them. Most chemical reactions within a cell occur in the cytoplasm. Cell MembraneFlexible, double layered membrane that supports the structure of the cell and keeps cytoplasm and all organelles contained but still allows small molecules like water and oxygen to easily pass through.
Large molecules like proteins can’t transfer therefore membrane known as “semi-permeable”. NucleusSpherical dark structure within the cell that contains genetic information that controls all cell activities. Contains chromosomes which contain DNA (deoxyribonucleic acid) which carries coded instructions for all of the cells activities. During cell division the exact same DNA is replicated in the new cell. MitochondriaCells contain many mitochondria which make energy available for the cell in the form of glucose (sugar). Active cells like muscle cells contain many mitochondria where as fat cells contain less.
The mitochondria use enzymes to convert stored energy into useable energy in a process called cellular respiration that requires oxygen (glucose + oxygen -;gt; carbon dioxide + water + useable energy). Cells in which cellular respiration has to happen very fast such as muscle cells have many mitochondria. Endoplasmic ReticulumThree dimensional network of tubes and pockets that transport proteins and nutrients thorough the cell. Very important in many types of cells such as in the brain it assists with the release of hormones, in muscles it is involved with muscle contraction.
Golgi BodiesCollect and process material to be removed from a cell, and also create mucus. Cells that secrete a lot of mucus such as cells lining the intestines have many Golgi bodies. Plants Only Cell WallFound just outside the cell membrane is rigid but porous and provides support for the cell against physical injury. Cell walls are composed of cellulose and the cellulose in a plant can hold it together long after it died. VacuolePlants cells usually have one large vacuole which are full of water and keep the cells plum which keep the plant’s stem and leaves firm.
If vacuoles lose water pressure, leaves and stems become soft and droops until water is replaced. ChlorplastsChloroplasts contain chlorphyll and give leaves their green colour. Most important chlorplasts absorb light energy and create glucose and oxygen for the plant to convert to energy through photosynthesis (carbon dioxide + water + energy (sunlight) -> glucose + oxygen). Photosynthesis allows plants to create their own food but though they can get glucose and oxygen from the sun, they still need mitochondria to convert it to a useable energy.
Differences between plant and animal cells •Animal cells have only cell membranes •Plant cells have cell membranes and cell walls, as well as many plant only organelles such as chloroplasts and vacuoles Cell Division Importance •Reproduction: oCharacteristics for life oAll living things must reproduce oEvery time a cell divides it produces two cells which can be ? Identical – Asexual reproduction (Mitosis) ?Different – Sexual Reproduction (Meiosis) •Growth oAll living things must grow When a multicellular organism grows, it increases in number of cells oUnicellular organisms will only slightly enlarge oCells only grow so big because: ?All cells need Oxygen, Water and Sugar which needs to be transferred to and through the cell ? Cells also need to transfer CO2 and other waste products out of the cell ? If a cell gets too large than it cannot transfer enough of its necessary nutrients in and out of the cell to satisfy the larger volume ? The cell will then either die from lack of nourishment (no O2 or sugar) or from poisoning (no waste removal) •Repair Every day the body sheds millions of dead skin cells and replaces them oRed blood cells are replaced every 4 months oCuts and bones need to be healed Diffusion and Osmosis •Diffusion occurs when a high concentration of a substance moves to a lower area of concentration to balance the concentration oConcentration: the amount of substance in a given solution •Osmosis is the movement of water from high to low concentrations •If a cell is too big it cannot diffuse necessary nutrients fast enough which usually leads to the death of the cell. Limit on cell size If a cell gets too large than it cannot transfer enough of its necessary nutrients in and out of the cell to satisfy the larger volume Cell cycle Interphase (G1-Gap 1, S-Synthesis, G2-Gap 2) •G1: Growth of Cell •Synthesis: DNA is duplicated and organelles are duplicated •G2: Cell prepares for cell division Mitosis •Prophase: DNA and chromosomes condense and thicken, Nuclear membrane breaks down, Centrioles move to opposite poles of the cell, Spindle fibres begin to form •Metaphase: Spindle fibres move chromosomes to equator of the cell and ine up, •Anaphase: Centromere (structure that keeps chromatids together) splits apart, each chromatid pair splits, two daughter chromosomes created, spindle fibres shorten and thicken and pull daughter chromosomes to opposite polls •Telophase: Daughter chromosomes are at opposite polls of the cell, begin to unwind and become thin and lose visibility, nuclear membrane starts to form around each group of chromosomes, spindle fibres begin to break down, cell membrane starts to pinch leading into cytokinesis Cytokinesis •Cell divides fully with the two separate nuclei and the organelles being split up.
In an animal cell the cell slowly pinches and divides, in a plant cell a cell barrier is put up and then a cell wall is eventually formed. Checkpoints in the Cell Cycle (pg 43) •During the cell cycle cell’s activities are controlled at specific checkpoints by specialized proteins sending messages to the nucleus. The nucleus interprets the messages and decides whether or not to remain in interphase. It will not divide if: oSignals from surrounding cells tell the cell not to divide oThere are not enough nutrients to provide for cell growth oThe DNA within the nucleus has not been duplicated The DNA is damaged •If the DNA is damaged early enough in the cell cycle, it may be able to be repaired, it is too late the cell is usually destroyed. Differences between Cancer and Normal cells •Cancer cells divide uncontrollably creating tumours •Some tumours are cancerous others are not •Cancerous ones can have cancerous cells split off from the tumour and spread the cancer to other parts of the body Lifestyle choices to reduce risks of cancer •Reducing exposure to carcinogens such as illegal drugs and tobacco •Eating a healthy diet and staying at a healthy weight (don’t be fat) Treatments for cancer Surgery: Physically remove the cancerous tissue •Chemotherapy: Uses drugs to try and treat cancer by slowing or stopping the cells from dividing and spreading to other parts of the body. Many side affects that can include nausea, fatigue and hair loss •Radiation: Easily damaged by radiation because they divide rapidly and the DNA is damaged by the radiation and cannot divide further. Though there are minimal side effects, the radiation can cause other diseases later on from radiation exposure. •Biophotonics: Uses beams of light to detect and treat cancer. Not very common yet. Specialized Cells (2. 9) Have special physical and chemical differences that allow them to perform different jobs Nerve, Muscle, Red Blood Cells, White Blood Cells Function of Guard Cells (Control opening and closing of openings in plants, plant only) Hierarchy of animals and plants •Cells: A specialized cell that performs a certain function •Tissues: A collection of similar cells that perform a particular function •Organ: One or more tissues working together to perform a function •Organ System: Group of organs and structures that work together to perform a vital body function •Organism: Many different organ systems working together
Label diagrams of animal systems in Chapter 3 •Digestive System •Circulatory System •Respiratory System Arteries, veins, aorta, pulmonary veins/arteries, parts of heart •Circulatory System consists of Blood Vessels, Blood and Heart •The heart pumps blood through the blood vessels •Arteries take blood away from the heart •Veins return blood to the heart •Blood caries O2 towards and CO2 away from tissues •Pulmonary Artery carries oxygenated blood from the heart to eh lugns •Pulmonary Vein carries oxygenated blood from the lungs to the heart Artery walls are thick, very elastic and have more muscle •Veins are thin walled and contain valves to push the blood along •High pressure in the arteries so that the blood can get to all the parts of the body •Once blood has left the tissues and enters the vein, blood is very low pressure •Capillaries are smallest blood vessel and are only 1 blood cell wide. Gases are diffused in between the capillaries and surrounding tissue Blood •Consists of Water, Red Blood Cells, Plasma, White Blood Cells, Platelets •Carries Oxygen, CO2 and nutrients from the digestive system Difference between stroke and heart attack Heart attack is the failure of the heart, stroke is a burst or blocked blood vessel in the brain that leads to brain damage, and/or death Explain Gas Exchange, in lungs and cells •In the lungs, alveoli have high concentration of oxygen and low concentration of CO2, capillaries have low concentration of oxygen high concentration of CO2. To even out these high concentrations they exchange gases so that the capillaries gain oxygen and lose CO¬2, and the alveoli lose oxygen and gain CO2. Blood from the capillaries then goes to the heart and is pumped around the body to different tissue where a similar exchange occurs.
Tissue has low concentration of oxygen and high concentration of CO2 due to the cellular respiration, and the blood has high concentration of oxygen, low concentration of CO2. The gases exchange as before and the blood ends up with high concentration CO2 and the tissues with high concentration oxygen. Diagram on Page 108 (VERY IMPORTANT)? Light/Optics Light is an electro-magnetic energy wave that eyes can perceive. There are other types of electro-magnetic waves. As seen in the chart -> Energy increases in the colour of the light as well with Red having the least energy and Purple having the most.
Energy also increases with frequency of the waves radio waves having less and gamma rays the most. Light comes from all objects we see. All objects are either luminous (produce own light) or non-luminous (doesn’t produce own light but reflects light from another source). Light Sources (brackets are easy to remember keywords): Incandescence (Filament, regular light bulb) is light created from certain materials reaching high temperatures such as a filament in an incandescent bulb or metal when it is being smelted.
Filaments in incandescent bulbs are so hot that if oxygen was present they would burn up instantly which is why non-reactive gases are used to fill the bulbs to keep the filaments from burning. Light is also created from electric discharge (electricity passes through a gas) which is where light is produced through an electric current passing through a gas to create a light. Neon lights are an example of this where Neon gas in a closed circuit is charged with electricity to create a glow. Lightning is also an example where the gas is the air in the Earth’s atmosphere.
Light from phosphorescence (glow-in-the-dark, absorbs light in the day, gives off at night) is the creation of light through “glow-in-the-dark” materials. These materials absorb energy during the day and keep some of the energy to release during the night. Their giving off of light can be limited to a few seconds up to a few days depending on the material. Light from fluorescence (takes ultraviolet light immediately releases as visible light) occurs when an object absorbs ultraviolet light and immediately releases the energy as visible light.
Many detergent companies add fluorescent dyes to their detergents to make clothes seem like they are glowing. Fluorescent lights though are the most common example of this light production and they are a combination of fluorescent light as well as electric discharge light. The tubes are filled with low-pressure mercury vapour and when an electric charge is put through the tube, the mercury creates ultra-violet light and fluorescent material in the tubes creates fluorescent light. Fluorescent lights are 4 to 5 times more efficient than incandescent lights.
Chemiluminescence (chemical reaction light) light is the light created from a chemical reaction and an example is the light sticks where you shake it and it starts to create light. Bioluminescence (biological chemical reaction) is light created organically in organisms like fire flies. It occurs through a chemical reaction between oxygen and luciferin. Triboluminescence (rocks) is the light created when certain rocks are rubbed together LED (Light Emitting Diodes): An electronic device that allows an electric current to flow in one direction, using semi-conductors, which creates light.
LEDs are extremely efficient and produces very little heat and will likely become the most popular lighting source in the future. Laser (Light Amplification by Stimulated Emission of Radiation): Unlike the above light sources which output electromagnetic rays at different energies and directions, lasers differ because their light is produced with only one energy level and one direction. Lasers also differ because when they are pointed into a triangular prism, the light doesn’t separate into different colours.
The light from lasers is very intense because all the energy and light is going in one direction which is why the beam is narrow, pure in colour and very intense. A high energy laser can cut through steel, and other types of lasers have been used to measure the Earth-Moon distance with an accuracy of 3 cm. Ray Model of Light: The light theory that states that light from a luminous object goes out in straight rays in all directions. With light going out in straight rays, geometric optics is possible. Specular reflection: The reflection of a smooth, shiny surface such as calm water or a flat mirror. fig. 2) Diffuse reflection: The reflection off an irregular or dull surface that is not consistent (fig. 5) Flat Mirrors Most Mirrors consist of two parts: Front part is sheet of glass, and back part is a thin layer of reflective silver or aluminum. When we look at a flat mirror, our brain perceives that the object is behind the mirror, which is why it is called a virtual image. Mirrors also reverse the image laterally (left to right). Laws of Reflection 1. The Angle of Incidence Equals the Angle of Reflection 2. The incident ray, the reflected ray, and the normal all lie in the same plane.
The laws do not take the same effects on mirror surfaces that are not flat Virtual Image: The image formed by light coming from an apparent light source that is not real; the appearance of something behind a mirror is a virtual image SALT 4 Characteristics: 1. Size of Image (Compared to the object: same size, smaller, larger) 2. Attitude of image (which way the image is oriented compared to the object: upright or inverted) 3. Location of Image 4. Type of Image (Real or Virtual) SALT: Size, Attitude, Location, Type An image in a plane mirror is always the same size as the object, upright, behind the mirror, and virtual.
Curved Mirrors Concave (Converging) Mirror: A mirror shaped like part of the surface of a sphere in which the inner surface is reflective. (conCAVE, cave’s go inward) Convex (Diverging) Mirror: A mirror shaped like part of the surface of a sphere in which the outer surface is reflective. Centre of Curvature: The centre of the sphere whose surface has been used to make the mirror Principle Axis: Line through the centre of curvature to the midpoint of the mirror. Vertex: The point where the principal axis meets the mirror. Focus: Where rays parallel to the principal axis converge in a concave mirror.
Light rays parallel to the principal axis will be reflected off a concave mirror through a single point. This point, where parallel lines converge, is calls the focus. Due to parallel rays focusing at F(the focus), this type of mirror is also called a converging mirror because the reflected rays converge. Locating Images in Concave Mirrors To determine the image of an object in front of a concave mirror you need to draw at least two incident rays from the top of the object. These rays will be reflected off the mirror and may or may not cross to form an image.
The following rules for concave mirror can be used to determine the characteristics of images at a variety of object locations. Uses of Concave Mirrors With light source at F(focus) the light rays reflect of the mirror and produce parallel beams of light. Used in flash lights, search lights, and car head lights. The reverse of this is used to capture sunlight or other energy waves such as in a solar cooker where the pot is located at F(focus) to gain the most heat from the sun, or a satellite dish which has the receiver at F(focus) to collect the most waves.
Locating Images in Convex (Diverging) Mirrors: The parts of a convex mirror are similar to those of a concave mirror except that the F(focus) and C(centre or curvature) are located on the opaque side of the mirror. Images appear smaller, upright and are virtual images. Convex mirrors are useful in showing a wide range of view in a smaller virtual image. Convex mirrors are used as security mirrors in stores as well as side-view mirrors on cars because a large area can be shown in a relatively small virtual image.
Due to it being proportionally smaller than the real object, “Objects in mirror are closer than they appear” is usually printed on side-view mirrors so that drivers are aware of this. As seen above a convex mirror always produces a smaller virtual image. Refraction Refraction is the change in the direction of light due it moving from one medium to another. When it changes medium the speed of light changes and the angle from the normal changes resulting in visible change in the path of the light. Lights speed in a vacuum is 3. 00 x 108 m/s where as in water it is 2. 26 x 108 m/s.
This change in speed results in refraction. Shown to the left are the different measurements needed to calculate refraction. Normal is perpendicular to line of refraction. Line of refraction is the line that separates the two mediums Angle of incidence DOESN’T equal angle of refraction. Speed of light changes when it goes from one medium to another. When it slows down it the angle of refraction decreases and goes closer to the normal when it enters the new medium. When it speeds up the angle of refraction goes farther away from the normal when it enters the new medium.
Refraction also usually includes some reflection from the light that strikes the new medium. Index of Refraction/Snell’s Law n-refractive index c-speed of light in a vacuum v-speed of light in the material i-angle of incidence r-angle of refraction Snell’s Law to find bending of light from one medium to another. n1sinO1=n2sinO2 ExplanationEquation Basic equation to find indexn=c/v To find nn=sini/sinR To find vv=c/n Medium 1n=sin Ov/sin O1 Medium 2n=sin Ov/sin O2 n1 – the refractive index of the first material n2 – the refractive index of the second material
O1 – Angle of refraction O2 – Angle of refraction Total Internal Reflection When light travels from one medium to another and the second one has a higher speed of light, the angle of refraction will be larger than the angle of incidence as the light bends away from the normal. Due to this relationship between the angle of incidence and angle of refraction, there comes a point where the angle of incidence will cause the angle of refraction to be 90 and it will simply go along the top of the first medium, never leaving it.
This angle of incidence that causes it is called the critical angle. If you increase the angle of incidence past the critical angle it ends up not leaving the medium but reflecting back into it. The refracted ray disappears and only the reflection is visible. This is called total internal reflection. Total internal reflection is met when two conditions are met: light is travelling slower in the first medium than the second, and the angle of incidence is large enough that no refraction occurs in the second medium but instead reflects back into the first medium.
Diamonds are so appealing because they have a lot of total internal reflection due to their cut resulting in a critical angle of 24. 4 . Therefore a lot of incident light reflects inside the diamond and reflects multiple times before coming out of the top of it. This gives it the sparkling effect and makes them so appealing. Fibre optics take advantage of total internal reflection because due to their extremely small critical angle, they can carry light for very long distances without much of it leaving the medium. That is why fibre optics are used in many communications networks such as cross continent cables to carry phone ines, television and internet. Using fibre optics allows data to travel at the speed of light but fibre optics are also extremely durable and very good for this purpose. They are also used in medical machines such as an endoscope, which is used to check the health of some human organs. A triangular prism of glass can exhibit total internal reflection with the light ray coming back out parallel to the incident ray. This is why some triangular prisms are used in periscopes and binoculars to change the path of light.
Retro-reflectors are similar except they return the light to the same spot it entered the medium and is used on bike reflectors and some signs. Refraction results in depth perception being distorted with objects in water, the apparent flattening of the sun due to its refraction through the changes in air density in the atmosphere, the appearance of water on pavement on a hot day due to the bending of light due to extreme heat nearer to the pavement and changes in density. Dispersion is the separation from white light into its constituent colours, which is seen in a triangular gas prism or in a rainbow.
This happens because when the colours are divided in the prism, each colour has a slightly different speed so when it refracts you can see all the colours. This happens similarly with a rainbow but with little water droplets instead of triangular prisms. Lenses Converging Lens: A lens that is thickest in the middle and causes the incident parallel rays to converge to a single point after refraction. Diverging Lens: A lens that is thinnest in the middle and that causes incident parallel light rays to spread apart after refraction.
Due to the light passing through air to glass and back to air, two refractions occur, from air to glass, and then from glass back to the air. Refractions become more visible with wider lenses as seen right. As seen below, there are a few common rules similar to those of converging. There are also examples of images created by the lens, below. Below are the rules and images created by a diverging lens also similar to diverging mirrors. ? The Lens Equations Lens Terminology do= distance from the object to the optical centre di= distance from the image to the optical centre ho= height of the object i¬= height of the image f = focal length of the lens; distance from the optical centre to the principal focus (F) The Thin Lens Equation is used to relate the focal length, object distance and image distance and uses the following equation: The following sign conventions apply: •Object distances (do) are always positive •Image distances (di) are positive for real images and negative for virtual images •The focal length (f) is positive for converging lenses and negative for diverging lenses The following are examples of how to use the Thin Lens Equation to solve different questions:
The Magnification Equation is the comparison between the size of the object and the image. To find the magnification of the lens, the following equation can be used: The sign convention is the same as in the Thin Lens Equation but with the following additions: •Object (hO) and image (hi) heights are positive when measured upward from the principal axis and negative when measured downward. •Magnification (M) is positive for an upright image and negative for an inverted image The following are examples for The Magnification Equation: Lens Application The Camera: A converging lens is used in the camera to produce an inverted real image as long as the distance is greater than F’. Due to the camera taking an object and putting the real, smaller, inverted image on the sensor or film, the object must be at least twice the focal length away, farther away than 2F’. Because the film or sensor cannot be moved back and forth to create a clear image, the lens is moved so that the sharp image falls on the sensor or film. This is called focusing.
Film was the original way to capture images using flexible light sensitive film, but prior to that, photographers used glass plates covered in light sensitive chemicals. Film today is rarely used as the digital sensor allows uses a light sensitive device made of silicon to capture the image in a format readable by a computer or camera screen. Movie Projector: A movie projector is essentially the opposite of a camera because the small inverted object on the movie film is inverted and enlarged onto the movie screen. The film must be located between F’ and 2F’ for this to work. Also the film must be loaded upside down.
As with the camera many theatres have upgraded to digital projection, which allows the movies to be stored on a hard drive and not film. Magnifying Glass: A very simple lens application that uses a converging lens in which the object is located between F’ and the lens so that a larger virtual image is created and the human brain sees the image as being bigger and easier to see. Compound Microscope: This microscope is the arrangement of two converging lens, it produces two enlarge images, one real and one virtual. This real image is not seen due to restriction of your sight by the body tube.
It is the larger virtual image which you see and allows you to view the object at a higher magnification. Refracting Telescope: The telescope operates on the same principle as the compound microscope but the object is much farther away, so far away from 2F’ that incident rays appear to be parallel. A refracting telescope also creates two enlarged, inverted images: one real image that you don’t see (inside the tube of the telescope), and one larger, virtual image that you do see. The Human Eye The human eye acts as a converging mirror gathering light from a large area and inverting it into a small virtual image onto the retina.
The retina is a light sensitive tissue that allows the brain to “see” objects. The brain flips them upright so that we see it upright. To get a clear image, the lens changes width to ensure that the image lands clearly on the retina. When the eye focuses it is called accommodation. As the eye ages or becomes tired, the lens (focusing muscle) can lose its ability to focus as quickly or at all. When this becomes a permanent issue as comes with age due to the eyes lens’ loss of elasticity, glasses with converging lenses may be recommended to artificially correct it.
There can also be problems that arise such as hyperopia (far-sightedness) and myopia (near-sightedness). Hyperopia (far-sightedness) is cured by using converging lenses so the image appears clearly on the retina. Either glasses or contacts accomplish this by using a positive meniscus lens for cosmetic purposes but is still a converging lens. Myopia (near-sightedness) is cured by using diverging lenses so that the image appears clearly on the retina. Either glasses or contacts accomplish this by using a positive meniscus lens for cosmetic purposes but is still a diverging lens.