Presentation on theme: "Système Internationale SI Units. SI is a system of measurement used in science based on powers of 10. Units are given using a prefix + a base unit Base."— Presentation transcript:
Système Internationale SI Units
SI is a system of measurement used in science based on powers of 10. Units are given using a prefix + a base unit Base Units: Length = meter (m) Mass = gram (g) Volume = cubic meter (m³) or liters (L) Time = seconds (s) Temperature scale = celsius Prefixes: Kilo- (K) 1,000 Hecto- (H) 100 Deka- (D) 10 Base unit- 1 deci- (d) 0.1 centi- (c) 0.01 milli- (m) 0.001
To remember the prefixes… King Henry Danced By Dirty Cow Manure
Conversion: 80cm= _________meters 80cm x 1m/100cm = 2000mm = ___________meters 2000mm x 1m/1000mm = 2 Kg = __________-mg 2Kg x 1,000,000mg/1Kg = 0.8 m 2 m 2,000,000 mg
800mL = __________L 800mL x 1L/1,000mL = 7,500 cg = __________Kg 7,500 cg x 1Kg/100,000cg = 0.8 L Kg K H D b d c m -You can also count how many times you are multiplying or dividing by 10 and then move the decimal point as necessary
SI Practice Conversions 1)2,345 g = ______________Kg 2)3,462 mL = _____________DL 3) 6.2 Km = ______________dm 4) 78 Hg = _______________Kg 5) KL=_____________L 6) Km= _________mm 7) 520 cm = _____________m 8) dm =____________Dm 9) 1,236,000mm³=_________Km³ 10) 3.5 hours= ___________seconds 1)2.345 Kg 2) DL 3)62,000dm 4)7.8 Kg 5)1L 6)5mm 7)5.2m 8)8.922 Dm 9)1.236 Km³ 10)12,600 seconds
Elements, Compounds, and Mixtures We can describe matter based on its physical and chemical properties, but how do we organize it? Pure substances- any form of matter made of uniform particles Mixture- matter made of multiple types of particles that are not chemically bound
Pure substances are split into two categories… Elements- pure substance made up of only one type of atom -cannot be broken down into simpler substances by physical or chemical means Compounds- pure substance made up of multiple types of atoms, chemically bound to form particles called molecules
Elements are all made up of different types of atoms and organized according to their physical and chemical properties on the periodic table.
Compounds Compounds are made of chemically bound elements, but their properties can be different than the properties of the elements that make them. dangerous elements can make harmless compounds and vice versa A type of molecule is always made up of the same ratio of its component elements Examples- water is always 2 Hydrogen atoms and 1 oxygen -table salt is always 1 sodium atom and 1 chlorine atom
Compounds can be broken down during a chemical change. -Sometimes they need a catalyst, sometimes they need an input of energy, and sometimes they just degrade over time. Eat a steak, its proteins are broken down into amino acids (mechanical and chemical digestion) then your body reassembles the amino acids into other proteins (translation). Can you come up with any other examples of compound breaking down or being formed? Glucose Deoxyribonucleic acid
How do we know when a chemical change has taken place? Often the appearance (texture, color, physical state) can change. Other signs of change include… -heat -odor -fizzing and foaming -sound -light Unlike physical changes, chemical changes are hard to reverse -You can undo some reactions by chemical means, but most of the time it is difficult
Atoms: Theory and Structure- Review Atoms are the smallest unit of an element Each element is made-up of a different type of atom, distinguished by the number of the different subatomic particles that compose them. There are three subatomic particles that make-up an atom Proton: + charge and large mass (1amu) Neutron: 0 charge and large mass (1amu) Electron: - charge and small mass Protons and neutrons are found in the nucleus of the atom and electrons orbit around it, in what is called the electron cloud.
Atomic Theory: All substances are made of atoms, which in turn are made of smaller particles called electrons, protons, and neutrons. They can be divided or combined (difficultly)- nuclear fusion and fission Atoms of the same element will all have the same number of protons and electrons, but the number of neutrons and as a result the mass may vary (isotopes). Atoms do join with other atoms to form new substances (compounds)
Chemical Reactions Chemical reactions (chemical changes) occur when compounds form or degrade. This occurs as a result of chemical bonding, when electrons are shared, gained, or lost during the association of one atom with another Do all of an atom’s electrons take part in chemical bonding? No, usually only the valence electrons take part in chemical bonding
Valence electrons are the electrons on the outermost energy level -an atom can have between 1 and 8 of them -atoms bond with other atoms, gaining, losing, or sharing electrons, to get a complete set of 8.
Which groups of elements want to lose electrons? Which groups of elements want to gain electrons? Which groups will most likely share their electrons? There are different types of chemical bonds. The type depends on whether electrons are transferred or shared between atoms.
Ionic Bonding A type of bonding in which electrons are transferred from one atom to another Atoms are usually neutrally charged, having an equal number of + protons and – electrons, but during an ionic bond that number is no longer equal. In one of the bonding atoms, the number of electrons is greater than the number of protons. -they are negatively charged In the other bonding atom, the number of electrons is less than the number of protons. -they are positively charged
Charged atoms are called ions -positively charged ions are called cations -negatively charged ions are called anions Does an ionic compound, made of one cation and one anion, have a charge? No, the atoms in the compound are now charged, but the compound itself is neutral
Ionic compounds bond together in rigid, geometric structures or chrystals. -the actual shape in which they form is called a chrystal lattice
Identify the cation and anion in each of these ionic compounds CaCl2 Ba K2S FeBr3 Cr2O3 KI NaCl FeO KF FrBr
Usually when an atom has more than one or two electrons to gain or lose it cannot transfer its electrons. In these cases they will share electrons, forming covalent bonds Compounds formed of covalent bonds are called molecules -a molecule is the simplest form of a covalent pure substance Organic compounds (anything containing carbon) are all covalent. -glucose -starch -celullose
You can diagram a molecule using an electron-dot diagram or Lewis structure. Drawing an electron-dot diagram… 1)Write the element symbol of the largest atom 2)Draw dots around it representing its number of valence electrons 1)Try to space them evenly in groups of two 3)Place the other atoms around it in a way that allows each atom to have 8 valence electrons (2 for hydrogen).
-A pair of electrons involved in a bond can be represented using a bar. (single bond) -4 electrons involved in a double bond can be represented using a double bar (double bond) -6 by a triple bar (triple bond)
Other types of Chemical Bonding There are two other types of chemical bonding, metallic and hydrogen bonding They do not result in new compounds like ionic and covalent bonding. Instead they associate or hold like atoms together. Metals are usually very dense, meaning that their atoms are very close together. As a result their electron clouds overlap and their valence electrons are allowed to move throughout the substance. Hydrogen, because it is so simple an atom, when it binds with electronegative atoms (want to take electrons) becomes slightly positive. It will then associate with electronegative atoms of other molecules, limiting how far apart the different molecules can go without more energy.
Metallic bonding gives metals some unique properties, such as electrical conductivity, ductility, and malleability. Electrical conductivity- since the valence electrons can move freely through metals, an electric current (moving electrons) can also. Ductility- ability to be drawn into wire Malleability- ability to be hammered into sheets Basically, metal can be bent into any shape necessary and can be used to direct electricity.
As a result of hydrogen bonding, water molecules tend to stick together. This gives water molecules several unique properties…adhesion, cohesion, and surface tension Adhesion- water molecule’s tendency to stick to other objects Cohesion- water molecule’s tendency to stick to each other Surface tension- water molecule’s tendency to form a rigid surface at the top of a liquid These properties explain capillary action
Signs of Chemical Reactions Chemical reactions often give us physical evidence that a reaction is taking place. Such as… Color change Precipitate formation (forming a solid) Gas release (creating a gas) Heat (energy release)
Compounds are represented using chemical formulas (e.g. H2O) and chemical reactions are represented using chemical equations. 6 CO2 + 6H2O C6H12O6 + 6O2 Chemical equations tell you the chemical formulas of all of the compounds involved and how many of each compound is involved. We know… -the number of each compound -The kinds of atoms involved -the number of each kind of atom The compounds entering the reaction are called reactants The compounds produced in the reaction are called products
The one BIG rule The atoms in the reactants much equal the atoms in the products The Law of Conservation of Mass -Mass (matter) is neither created nor destroyed during a normal chemical or physical reaction As a result the atoms present before a reaction must also be present after a reaction
To balance equations and make sure that no matter is lost or created, we use coefficients. -they tell us how many of a particular compound is involved in a reaction -By adding them to one, two, or all of the compounds involved in a reaction we can be sure that the same number of atoms enter and leave a reaction. CO2 + H2OC6H12O6 + O2 6CO2 + 6H2OC6H12O6 + 6O2 Balancing chemical equations is part of a branch of chemistry called Stoichiometry
Energy Energy is the ability/potential to do work (move matter). When matter interacts energy is transferred back and forth. Something with a lot of energy could do a lot of work Or To do a lot of work (moving something massive), it requires a lot of energy
Energy in Chemical Reactions Iron reacts with oxygen to form rust. How come your car doesn’t spontaneously rust and fall apart? Plants bond carbon dioxide and water to make glucose, why can they not do this without light? How come, after you remove the initial flame from a candle, it continues to burn? The answer is energy energy is transferred, released, or absorbed whenever chemical bonds form or break This causes some reactions to take place very slowly, some to take place very quickly, some to require a constant or initial input of energy, and some to release energy to the environment.
Energy is absorbed when chemical bonds break and released when they form. If a chemical reaction absorbs more energy breaking up its reactants than its products release while being put together, then the reaction is called endothermic. -Endothermic- heat enters -Endo- inside Photosynthesis is an endothermic reaction -the absorbed energy comes from the sun
If a chemical reactions releases more energy bonding its products than it absorbs breaking its reactants, then the reaction is called exothermic. -Exothermic- heat exits -Exo- outside-exit Cellular respiration is an exothermic reaction -the energy released from breaking up glucose fuels our bodies
Some reactions will occur spontaneously without any initial input of energy, but most of the time, even exothermic reactions need an initial input of energy to get them started. The amount of energy a reaction needs to get started is called activation energy Exothermic reaction- heat energy given off by products Endothermic reaction- heat energy stored by products
The speed at which reactants break and products form during a chemical reaction is called its reaction rate. Reaction rate is affected by how exposed the reactants are to each other and the amount of ambient energy to start the reaction. To speed up a reaction… Increasing the temperature increases the amount of energy Increasing the concentration of the reactants, the surface area on which the can react, adding a catalyst, or removing an inhibitor increases how exposed the reactants are to each other. Catalyst- anything that lowers the activation energy required to start and maintain a reaction Inhibitor-anything that increases the activation energy required to start or maintain a reaction. -neither catalysts nor inhibitors are chemically changed during a reaction
Color Quiz 1)Does a catalyst increase or decrease reaction rate? Black- increaseorange-decrease 2) What is activation energy? Black- energy needed to start a reaction Orange- energy gained during a reaction 3) During an exothermic reaction, is the net energy gain positive or negative? Black- positive Orange- negative 4) During an exothermic reaction, the products … Black- absorb heat Orange- release heat 5) During an endothermic reaction, is more heat absorbed or released? Black- released Orange-absorbed 6) Photosynthesis is an example of what type of reaction? Black-endothermic Orange-exothermic
Energy associated with the motion and position of objects is called mechanical energy. It is split into two types, kinetic energy and potential energy. Kinetic energy is the energy of motion, describing how an object moves. Potential energy is the energy of position, describing the potential an object has to move as a result of its position in the universe. Mechanical energy = Kinetic energy + Potential Energy
Kinetic energy depends on the mass of an object and how fast it is moving (its velocity). E K = (1/2)mv 2 E = energy K= type of energy M= mass V= velocity Which value affects an objects kinetic energy more, mass or velocity? (p.241 practice)
Potential Energy comes in two forms, elastic potential and gravitational potential. Elastic potential energy is an objects potential to spring back after being stressed somehow. e.g- stretching rubber band, drawing back a bow, compressing a spring Gravitational potential energy is an objects potential to move as a result of gravity (to fall). It depends on the height of an object and its weight (mass and force of gravity) E g = mgh E= energy G=type of energy M= mass G= acceleration of gravity (9.8m/s²) H= height It can also be given as… Gravitational potential energy = weight x height P.242 practice
When an object falls or an elastic is released, its potential energy is converted into kinetic energy, but the total amount of energy stays the same. When the ball hits the ground and stops moving, its mechanical energy is gone. Where did it go?
Energy that appears to be lost is really just transferred into a new form. There are seven forms of energy… 1)Mechanical energy-energy associated with motion and position 2) Thermal energy- energy associated with heat (vibration of particles) 3) Chemical energy- energy stored in chemical bonds 4) Electrical energy- energy associated with moving electrons 5) Sound energy- energy of vibrating objects moving in waves through matter 6) Light/radiant energy- energy moving through electromagnetic waves, can travel outside matter 7) Nuclear energy- energy stored in the nucleus of an atom and released during fission and fusion We will talk in detail about heat, light, and sound later
Energy is converted from one form to another constantly and is involved in nearly every event or occurrence in the universe Example: Mechanical energy of water (kinetic), transfers to a turbine that converts mechanical energy into electric energy. A light bulb then converts that electrical energy into radiant and thermal energy that is transferred to the particles in the room around the light. Your eye receives the radiant energy and converts it back into electric energy that travels through your optic nerve and to your brain. The purpose of a lot of the machines that humans use is to convert energy from one form to another. -the engine in a car converts chemical energy in gasoline into thermal and kinetic energy.
Hydrotubine Wind turbine
No machine or natural energy conversion is 100% effective, though, so where does the energy go? The Law of Conservation of Energy says that energy cannot be created or destroyed -There is more energy in your food than you can use as fuel to move. -There is more energy gasoline than your car can use to move. Whenever an object moves, there is a force that pushes in the opposite direction that resists its motion. This force is called friction. The energy wasted to overcome friction is converted into thermal energy. Thermal energy, waste energy, is released in every energy conversion.
How efficient a machine or process is depends on how much energy is wasted overcoming friction. The less thermal energy released during an energy conversion, the more efficient it is. The more energy efficient a process is, the less fuel it needs in the first place.
Energy Resources Our energy resources on earth are split into two groups, renewable and nonrenewable. Renewable resources can be regenerated or provide an unlimited supply of energy. e.g. biomass (regenerated), wind, solar (unlimited supply) Nonrenewable resources cannot be regenerated under reasonable means. There is a finite supply of them on earth. e.g. fossil fuels, uranium -basically anything that comes from mining
Energy resourceAdvantagesDisadvantages Fossil fuels -High energy output -Easy to access and transport -Can be used to generate electricity and produce synthetic materials -are nonrenewable -produce smog -can produce acid rain -risk of spills Nuclear -concentrated form of energy -no air pollution -produces radioactive waste -is nonrenewable Solar -limitless source of energy -no pollution -expensive to harness on large scale -only useful in sunny areas Water -is renewable -does not produce air pollution -requires dams, which distrupt ecosystems -only available near rivers Wind -is renewable -relatively inexpensive -does not produce air pollution -only practical in windy areas Geothermal -almost limitless source of energy -plants require little land -only practical near hotspots -produces waste water, which pollutes soil Biomass -is renewable -is inexpensive -requires large areas of farmland -produces smoke
Color Quiz There is a limited supply of _______________ resources. Red- renewableGreen- nonrenewable Which is an example of a nonrenewable resource? Red- windGreen- fossil fuels Which is an example of a renewable resource? Red- solarGreen- uranium (nuclear) Which force opposes all motion? Red- frictionGreen- gravity A process that creates a lot of heat as a biproduct would be called energetically __________________. Red- efficientGreen- inefficient The form of energy associated with the movement and position of objects is ______. Red- mechanical energyGreen- chemical energy The biggest downside to hydroelectricity is ________________. Red- ecosystem damageGreen- air pollution
What is Temperature? Temperature is the average of kinetic energy of the particles in an object or area. It tells you on average, how fast the particles are moving (vibrating or bouncing around). -all particles are moving at different speeds and in different directions, so the temperature of a whole object is just an average. If something has a high temperature, its particles are moving quickly. If something has a low temperature, its particles are moving slowly. Think about state changes… Which has a higher temperature -solids or liquids? -liquids or gases? What changed to cause the solid to melt? The liquid to vaporize?
What is thermal expansion? As objects increase in temperature and their particles move more, they spread out. -the whole object swells as a result. This is called thermal expansion Thermal expansion allows thermometers to work… It causes your doors to stick in the summer… It causes hot air to rise (if volume increases and mass stays the same, density decreases)… Buildings built in places where the temperature changes a lot have to be built with thermal expansion in mind.
How is temperature measured? Temperature is measured on any of three scales, Fahrenheit, Celsius, or Kelvin. Fahrenheit is used in the U.S, but not in science. Celsius is used internationally and in science because it is based on the freezing and boiling temperatures of water. Kelvin is also used in science, but it is centered around absolute zero. Absolute zero- temperature at which all particle energy motion stops. Particles have zero kinetic energy. -There are no negative values in the Kelvin scale, but there are in the Celsius and Fahrenheit scales. Converting from one scale to another… F = 9/5 C + 32 C= 5/9 (F-32) K= C ° C = 273° K = 32°F
What is the scientific meaning of the word…Heat? Heat is the energy transferred between objects at different temperatures. When an ice tray is placed in the freezer, heat is transferred from the water to the air in the freezer. When the water loses enough heat (energy) it freezes. Heat is always transferred from the higher temperature object to the lower temperature object. -to make something cooler, you take away heat, you don’t add cold. The greater the difference in temperature, the faster heat is transferred. -think of heat as rolling down hill, the greater the difference in temperature the steeper the hill.
When an object is heated, the energy is transferred in the form of thermal energy. An object’s thermal energy is the total kinetic energy of the particles in an object or area vs Temperature, which is the average kinetic energy of the particles in an object or area Thermal energy depends on amount, temperature does not. Whether heat is transferred between two objects depends on their temperatures not their thermal energy.
Some objects increase in temperature faster than others. How well they conduct thermal energy is called thermal conductivity. -leather seats compared to cloth seats in a car. Objects that conduct thermal energy well have a low specific heat. Specific heat is the amount of energy needed to raise the temperature of 1Kg of a material 1°Celsius or Kelvin.
Unlike temperature, heat cannot be measured. It must be calculated. Heat (joules) = (specific heat) (mass -Kg) (change in temperature- C° or K°)
Heat can transfer from one object to another in several different ways. Radiation- the transfer of energy by electromagnetic waves (e.g. light, infrared etc.) -can transfer through empty space outside of matter Conduction- the transfer of energy through direct contact of their particles -the hot pavement conducts its energy into your bare feet. Convection- the transfer of energy by moving currents of water or gas -the cooling effect of wind or moving water
Materials that conduct thermal energy well (usually with a low specific heat) are called conductors. -they exchange heat quickly -e.g. baking pan Materials that do not conduct thermal energy well (usually with a high specific heat) are called insulators. -they do not exchange heat quickly -e.g. oven mitt
Most of the energy on earth comes from the sun through radiation. We can survive because the atmosphere lets some forms of electromagnetic radiation through but not others. It allows light through but blocks most ultraviolet light. -damage to the ozone layer limits ability to do this Greenhouse gases help keep that energy on earth and limit how much bounces back out into space. They act as a thermal insulator. -too few greenhouse gases and half of the planet would freeze over each night. -like wearing a t-shirt in January -too many greenhouse gases and the earth will over heat -like wearing a sweatshirt and jacket in August
Electromagnetic Radiation and Sound Waves
What are waves? They are disturbances caused by the movement of energy, either through matter or through empty space. As a wave moves across the ocean, each water molecule only moves up and down. They do not flow all the way to the shore. As kinetic energy passes from one particle to the next, each particle performs the same motion (like dominoes falling).
If you are floating in a boat on the ocean, do the waves carry you all the way to shore? No, the energy makes the boat go up and down, just like the water molecules, and then it continues on. What does a surfer have to do to catch a wave? They have to paddle the same velocity as the wave of energy is moving until it breaks and they can let gravity carry them (like sliding down a ramp that keeps growing).
When energy is moving through matter, that matter is called a medium. Waves that can only travel when in a medium are called mechanical waves. e.g. sound waves, ocean waves, earthquake waves Waves that do not need a medium to travel through are called electromagnetic waves. They can travel through matter, but they can transmit energy without it. e.g. light, microwaves, infrared, ultraviolet, x-rays, gamma rays
Not all waves follow the same path. Some vibrate perpendicular (a right angle) to the direction motion, called transverse waves -they can vibrate up and down or side to side. -they look like traditional ocean waves. -electromagnetic waves are all considered transverse waves, while only some mechanical waves are transverse. The highest point of a transverse wave is called the crest And the lowest point is called a trough
When particles vibrate forward and backwards in the same direction as the wave is moving, it is called a longitudinal wave. -they are made as matter sequentially stretches and squeezes. -stretching or spacing out particles is called rarefaction. -squeezing particles together is called compression. Sound waves are all longitudinal waves.
Waves are described by several key properties… Amplitude, wavelength, frequency, and wave speed. Amplitude- how high or far a particle vibrates from its rest position. -High energy waves lead to greater amplitude Wavelength (λ)- the distance between the crests or compressions of a wave. -High energy waves have shorter wavelengths (waves are close together). Frequency (f)- number of waves in a given amount of time -the unit used is usually hertz (1Hz = 1wave/second) Wave speed (v)- the speed at which one wave travels. v = (λ)(f) If given two of the following, wavelength, wave speed, and frequency, you can solve for the third.
What happens to waves when they collide with a new medium or with another wave? When interacting with another medium, waves can reflect, refract, or diffract. When multiple waves interact, we get interference.
When a wave hits an object that it cannot transmit through, it bounces back. This bounce back is called reflection. An echo is an example of a reflection. The colors that you see are the wavelengths of light being reflected back. -if you see black, all colors are being transmitted and non is being reflected -if you see white, all colors are being reflected and non is transmitted. A mirror reflects light without distorting it
Why do we see rainbows after a sun shower? As light passes through the water particles in the air, it is bent. Different wavelengths (colors) bend more than others, so they separate. The bending of a wave as it passes from one medium to another is called refraction. As a wave passes through one medium to another, its wavelength and wave speed can change, but its frequency stays the same.
How come we can hear around corners but can’t see? Diffraction is a wave’s ability to bend around an obstacle. Waves with long wavelengths diffract more than shorter wavelengths. Light barely diffracts at all High pitched sounds diffract well Low pitched sounds diffract very well
What happens when two waves collide? For the moment that they are passing through the same space, we have something called interference. If two troughs or crests coincide, they add together and appear as one big wave -Constructive interference If a crest passes the trough of another wave, they take away from each other -Destructive interference
How do Noise Cancelling Headphones work?
When outgoing waves and reflecting waves interfere to create what look like static waves (not moving), we say that they have produced standing waves. The frequency at which standing waves are produced is called that object’s resonating frequency. When one object vibrates near the resonating frequency of another object, it can make that other object start to vibrate as well. Basically, one sound causes another object to start making a sound -This is called resonance
What is sound? Sound is a longitudinal wave of energy created by the vibration (oscillation) of matter that travels through a medium. Anything that is vibrating creates a sound, as it compresses and rarefacts the air particles around it. -we can only hear only hear the sounds of waves from objects vibrating at certain frequencies though. As waves travel through the air and through our ear, they cause hair cells attached to nerves to move, which sends signals to our brain. Different hair cells react to different frequency sounds. If they are damaged by high amplitude waves, we do not re-grow them. Your hearing peaked the day that you were born.
How fast do sound waves travel? The speed of sound waves depends on the medium they are traveling through. The denser and warmer the medium the faster the waves will travel. At high altitudes, where it is cold, sound travels slower than at room temperature. It travels faster through liquids and even faster through solids. If you put your ear to the ground, you can hear a train coming well before you could if you were standing. Mach 3 means 3x the speed of sound
Pitch, Frequency, Amplitude, and Volume The pitch of a sound (how high or low) depends on the frequency of the waves. -high frequency = high pitch The volume of a sound (loudness) depends on the amplitude of the waves. -high amplitude = loud -adding energy to a wave increases its amplitude -the loudness of a sound is measured in decibels Sounds over 120 dB can physically hurt
How do bats use sound? The reflection of sound is called an echo. Bats (and whales) use echoes to find objects and navigate in a process called echolocation. -electronic echolocation is called sonar. -an ultrasound is a procedure where sound waves beyond human hearing are used to find objects inside the human body.
Sound waves experience interference constantly. It can be either constructive or destructive. Constructive interference makes sounds louder Destructive interference makes sounds softer As an object approaches the speed of sound, the waves get so close together that constructive interference produces a wave with extremely high amplitude called a shockwave. The sound heard from a shockwave is called a sonic boom.
Most notes made by instruments are actually made up of several different waves at different frequencies combining through constructive interference. -the result is that note’s sound quality for that particular instrument. When different frequency sounds from different instruments or voices work together pleasantly, we say that they are in harmony. When they do not, it is cacophony.
What are electromagnetic waves? They are waves of energy, made of both electric and magnetic fields, that can travel either through a medium or a vacuum. What is an electric field? The field energy associated with charged particles (usually moving electrons). What is a magnetic field? The field of energy associated with moving charged particles or inherently polar materials. So…when charged particles move, they have both an electric and a magnetic field.
The two parts of an electromagnetic wave vibrate perpendicular to each other. When charged particles vibrate they produce electromagnetic waves.
How fast do EM waves travel? Like all waves, EM waves change speeds when they change mediums, but in a vacuum (without a medium), they travel 300,000,000 m/s. That is 186,000 miles per second Or 7.5 times around the earth per second. Nothing in the universe travels faster than light. -It is considered a cosmic speed limit There are theories regarding what would happen as you approached the speed of sound that include things like time travel and exponential mass increase.
EM waves vary in wavelength and frequency. The different types of EM waves (waves within a certain range frequency or wavelength) are laid out in a spectrum according to their frequencies and wavelengths. Low frequency, long wavelengths are one side. High frequency, short wavelengths are on the other.
In general, the shorter the wavelength/higher frequency the wave the more dangerous it can be. Radio waves- λ > 30cm- television and radio signals are carried by radio waves Microwaves- 30cm>λ>1mm-used in microwaves, cell phones, and radar Infrared waves- 1mm>λ> 700nm- most heat, especially from the sun, travels as infrared waves Visible light- 700nm>λ>400nm- all of the light and color that we see Long λShort λ
Ultraviolet waves- 400nm>λ60nm- caused skin damage (mutates cell DNA) but allows cells to produce vitamin D. X-rays- 60nm>λ>0.001nm- travels through most materials, used to see inside people, bags, etc. Gamma rays-0.1nm>λ- travels through most materials, used to treat some cancers The difference between x-rays and gamma rays is based more on source than wavelength (usually different types of radioactive material)
EM waves, just like any other wave, can reflect, refract, and diffract. Unless we are looking directly at a light source, any time we see an object, we are actually seeing the light reflecting off of it. When light bounces off a smooth surface (regular reflection) the different waves are still arranged the same way, so the reflected light looks the same as the source. -Mirrors When light bounces off of a rough surface (diffuse reflection), the different waves are reflected in different directions, so you just see a general mix of color. -Walls
When the energy from an EM wave transfers to matter rather than being reflected or transmitted, it has been absorbed. -Most light sources emit a wide range of EM waves, the colors we see are the ones that we not absorbed. Walls and even the particles in the air reflect light and send it in all different directions, this is called scattering. -This is why you can see even if you are not directly in a beam of light. Long wave length light diffracts better than short wavelength light, so it doesn’t scatter as easily. That is why for most of the day, the sky is a short wavelength color (blue).
Since light travels slower through air than it does through a vacuum, and slower through water than it does through air, when it hits these new mediums at an angle it bends. This is refraction. Short wavelength light refracts more than long wavelength light. -so violets and blues bend a lot and red bends little. This separation of colors creates rainbows.
Since EM waves have such short wavelengths, they do not diffract well, but they do diffract. This is why the edge of a shadow (penumbra) is fuzzy and lunar eclipses make the moon look red. Interference of light can take place, resulting in brighter or dimmer light, but it is hard to notice unless working with a light of only one wavelength (one color).
Why do we see the colors that we do? We see whatever wavelengths (colors) reach our eyes, which is determined by how materials, absorb, transmit, and reflect light. Objects that transmit all colors without scattering them are transparent. Objects that transmit colors but scatter them are translucent. Objects that do not transmit visual light are opaque.
With opaque objects, we see whatever light is reflected. Transparent and translucent objects appear to be whatever color they are transmitting. -a sprite bottle looks green because it transmits mostly green light and absorbs the rest. A pigment is any material/chemical that controls how a substance interacts with light and gives it its color.
How do we see color? There is a difference between primary colors and primary pigments. -primary colors are the wavelengths of light that can combine to produce a full spectrum of colors (produce white light). -primary pigments are the pigments/colors needed to make pigments that absorb all the different wavelengths of light (produces black pigment). -mixing paints is mixing pigments. Primary colors- green, blue, and red Primary pigments- cyan, yellow, magenta
Electricity and Magnetism
What is electric energy? How are charged particles different than neutral particles? Charged particles follow the law of electric charges, which states that like particles with like charges repel and opposite charges attract. The force, whether attractive or repulsive, that one particle puts on another is its electric force. The area in which this force works is that particle’s electric field.
Individual atoms and most compounds, in the natural state, are neutral (have the same number of electrons and protons). If electrons are lost or gained, a substance becomes electrically charged. If objects rub together (friction) they can pass electrons and become charged. If a charged material touches an uncharged material it can pass on electrons (conduction). If a charged material goes near an uncharged material its electric force can cause the electrons in the uncharged material to shift and create a charged area (induction). Electrons move to try to balance the charge of the system that they are involved in. They are not created or destroyed. They are conserved.
Substances that allow the free movement of electrons are called conductors e.g. metal (wires) Electrons will keep moving until they contact a positively charged substance. Substances that limit the movement of electrons are called insulators e.g. rubber (wire coating) Compounds held together by ionic or metallic bonds usually conduct electricity well. Covalent compounds do not. How much a substance opposes the flow of electrons is called its resistance.
What is static electricity? Static electricity is an electric charge when electrons are not moving from one object to another. The clothes in the dryer rub together, build-up a charge. When they stop moving, they stop passing electrons. They now stick together because of static electricity (+ sock sticks to – shirt) Objects don’t hold on to static electricity forever, eventually the built-up electrons will find some place to go. This is called electric discharge.
Electric discharge could be small and unnoticeable or large, loud, and bright. Electrons could pass harmlessly to particles in the air. Electrons could jump from your hand to a friend or door knob. Electrons could jump from cloud to cloud or from a cloud to the ground (lighting). As clouds move and build, they pass electrons and a static charge can build-up. When these charges jump from a negative cloud to a positive cloud or from a negative cloud to the positive ground we see and hear lightning. I hope no one ever feels it.
Color Quiz Electricity is a build-up of which type of particles. –Blue- chargedRed- neutral Particles with the same charge… –Blue- attractRed-repel Electric charges can be built-up through conduction, friction, or … –Blue- inductionRed- radiation The measure of how a substance allows electricity to pass through it is… –Blue-insulationRed- resistance Static electricity is different than current electricity because the charged particles… –Blue- do not moveRed- do move
How can we describe the movement of electrons? Electric current- The rate at which electrons move passed a certain point. Measured in amperes (amps) -Individual electrons don’t usually move very fast, but they will all start to move as soon as that option is made available, so your lights turn on quickly. When a current flows in only one direction it is called a direct current (DC). Current in batteries. When a current alternates which direction it flows it is called an alternating current (AC). Current moving through the wires in your house. -The direction alternates because the charge at the source (turbine at the power station) changes
Another way to describe electricity is voltage. Voltage describes the gradient between the positive and the negative charges. The larger the gradient, the more energy the electric current will carry and the faster its electrons will move. The batteries in a remote control have a voltage of 1.5. The current running through your house is 120 V. Lightning varies but can be 100,000,000 V.
Static electricity can’t do work. A current has to be present, which means that there can’t be a point in the system where electrons get stopped. A complete system or path through which electrons can flow without stopping is called a circuit. When you flip the switch on the wall, you complete the circuit and allow the current to flow. When you flip it again you break the circuit and stop the flow of electricity.
There are two main types of circuits, series circuits and parallel circuits. Series circuits are simple, single loops. Electrons all follow one path. -like cars going around a race track. Parallel circuits are more complex loops. Electrons have multiple paths that they could follow. -like roads around a city If a series circuit is broken any device (load) running on that current will stop functioning. If a parallel circuit breaks, one or two loads may be cut off, but electrons can find their way to the others. Your house is one large parallel circuit
Series circuit Parallel circuit
Electric currents can carry a lot of energy and be dangerous. What can you do to promote electrical safety?
What is a magnet? A magnet is anything that attracts iron (they work with other metals too, but iron is the most common). Magnetic materials have constantly moving electrons, the moving electric fields create magnetic force, the attractive or repulsive ability of a magnet. -All atoms have moving electrons, but in magnets they move in a way so that their respective magnetic fields add to each other rather than cancel each other out. Magnets also always have poles, opposite sides of the object that have opposite magnetic forces.
The poles of a magnet are labeled by how they interact with the magnetic field surrounding earth. -The north pole on a magnet orients itself towards the north pole. -The south pole on a magnet orients itself towards the south pole. -The North Pole on earth actually has the opposite charge as the north pole of a magnet. A compass is just a magnet allowed to spin freely.
What is an electromagnet? Since an electric current is comprised of moving electrons it has a magnetic field. Electromagnets wrap coils carrying an electric current into a tight bundle called a solenoid that increases the strength of the magnetic field. -the more moving electrons that can be squeezed into an area, stronger its magnetic field will be. This interaction between electricity and magnetism is called electromagnetism.
Describe some ways electricity is used productively in your life? What things can you do to ensure that the electricity around you is safe?
Since we see light that is reflected not absorbed, our eyes are adapted to recognize the primary colors, red, green, and blue. We have cones in the back of our eyes that send signals through the optic nerve to our brain. Each cone is adapted to receive either red, green, or blue light.
If someone is color blind, or color deficient, one or more of these cones does not function properly. It is an x-linked recessive disorder, which means the genes controlling the proteins inside these cones is on the X chromosome. It is expressed most frequently in men and is inherited from the mother’s side of the family.
What kind of technology have people developed to work with light (help us see)?