Energy

Energy

اسلاید 1: EnergyEnergy is a property that enables something to do workEnergy has various forms (kinetic, potential, rest energy)Kinetic energy is the energy of a moving object mv2KE = --------- 2It takes ~1000 N (or ~ 225 lbs) to hit a nail and drive it 5 mm into a surface.Visit www.worldofteaching.comFor 100’s of free powerpoints

اسلاید 2: Potential EnergyPotential energy is a capacity of doing some workPotential energy is the energy of positionGravitational Potential EnergyW = Fd = mgh = PE (potential energy)PE is relative!PE of a 1000-kg car at the top of a 50-m multilevel parking lot is:mgh= (1000 kg)(9.8 m/s2)(50 m)=490 kJ

اسلاید 3: Rest EnergyMass and Energy are related to each other and can be converted into each other.The rest energy of a body is the energy equivalent of its mass.E0 = m0c2E0 (m=1 kg) = 1 kg x (3 108)2 (cm/s)2 ~ 1017 JPE (m=1 kg, h=9 km) = mgh = 1 kg x 9.8 m/s2 x 9000 m ~ 105 J

اسلاید 4: Energy TransformationsMany mechanical processes involve interchanges between KE, PE, and work.Energy exists in some other forms: chemical energy, heat energy, radiant energy, etc.

اسلاید 5: Conservation of EnergyEnergy cannot be created or destroyed.It can only be changed from one form to another.The above statement is called the law of conservation of energy

اسلاید 6: Chapter 5Light and Atomic StructureLight and its propertiesAtomic structureInteraction between Light and MatterSpectrum

اسلاید 7: Light in Everyday LifeLight is a form of energy, radiative energy1 Watt = 1 Joule/sec Light has colorA prism split light into a spectrum (rainbow of colors)Light travels with a speed of c = 300,000 km/s

اسلاید 8: Rainbow

اسلاید 9: Interaction of Light and Matter Emission Absorption Transmission (passing through) Reflection (scattering)

اسلاید 10: Properties of LightLight behaves as both a particle and a waveLight particles are called photons, which can be counted individually.Light is also an electromagnetic waveThe wavelength is the distance between adjacent peaks of the electric or magnetic field 1 nm (nanometer) = 10–9 m 1μm (micron) = 10–6 mThe frequency is the number of peaks that pass by any point each second, measured in cycles per second or Hertz (Hz).light demo

اسلاید 11: Light is an electromagnetic waveLight consists of many individual photons.Each travels at the speed c and can be characterized by a wavelength and a frequency.

اسلاید 12: Many Forms of LightThe spectrum of light is called the electromagnetic spectrumDifferent portions of the spectrum are called:The visible light - what we see with our eyesThe infrared light - beyond of the red end of rainbowThe ultraviolet light - beyond the blue endRadio waves - light with the longest wavelengthsX rays - wavelengths shorter than ultravioletGamma rays - the shortest wavelength light

اسلاید 13: Electromagnetic spectrum

اسلاید 14: Electromagnetic spectrumFrequency units – Hertz1 Hz = 1 c1

اسلاید 15: Light and MatterThe amount of light is called intensityStudying spectra of celestial bodies one can learn a wealth of information about them

اسلاید 16: Atomic Structure92 chemical elements have been identified in the Universe.Nearly 20 more have been created artificially.Each chemical element is made from a different type of atom.Atoms are made from particles called protons, neutrons, and electrons.Protons and neutrons form the nucleus in the center of the atom.Electrons surround the nucleus.

اسلاید 17: Atomic StructurePositively charged protons are hold together by the strong force, which overcomes electrical repulsion.Negatively charged electrons are attracted to the nucleus.The number of protons in an atom is called the atomic number, which is unique for different chemical elements.The combined number of protons and neutrons in an atom is called the atomic mass number.Atoms of the same element with different number of neutrons are called isotopes.

اسلاید 18: Absorption and Emission in GasesSince electrons in atoms can have only specific energies, the atoms can absorb or release energy only in these amounts (quanta)Electron gets energy, jumps to an excited state,release the energy, and falls back downThe energy is emitted as a photon of light The photon has exactly the same energy thatthe electron has lost

اسلاید 19: Types of SpectraEmission line spectrum consists of photons emitted as each electron falls back to lower levelsAbsorption line spectrum appears when photons are absorbed, causing electrons to jump up in energyEach element or molecule produces its own distinctset of spectral lines

اسلاید 20: Emission by Hydrogen

اسلاید 21: Hydrogen lines in the visible

اسلاید 22: Examples of Spectra

اسلاید 23: Thermal Radiation``Complex’’ objects - planets, stars, people - produce thermal radiationIts spectrum depends only on the object’stemperatureHotter objects emit more total radiation per unit surface areaThe radiated energy is proportional to the fourth power of the temperatureHotter objects emit photons with a higher average energy

اسلاید 24: Temperature and Color

اسلاید 25: Temperature and Intensity

اسلاید 26: Reflected lightWhen the light (for example, sunlight) strikes anobject (ground, clouds, people), we see only thewavelengths of light that are reflectedDifferent objects (fruits, rocks, atmospheric gases)reflect and absorb light at different wavelengths

اسلاید 27: The Doppler ShiftRadial motion of a distant object can be determined due to the Doppler effectThe Doppler effect causes shifts in the wavelengthsof lightIf an object is moving toward us, its entire spectrum is shifted to shorter wavelengthsBecause shorter wavelengths of the visible light are bluer, the Doppler shift of this object is called a blueshiftThe Doppler shift of a moving away object - redshift

اسلاید 28: Doppler EffectDemo Doppler effect

اسلاید 29: SummarySpectral information gives us more knowledge about the objects (composition, surface temperature, moving properties)Visible light is only a small portion of the electromagnetic spectrumThe Doppler effect tells us how quickly light is moving toward or away from u