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Energy. Energy is a property that enables something to do work. Energy has various forms (kinetic, potential, rest energy). Kinetic energy is the energy of a moving object. m v 2 KE = --------- 2. It takes ~1000 N (or ~ 225 lbs) to hit a nail and drive it 5 mm into a surface.
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Energy Energy is a property that enables something to do work Energy has various forms (kinetic, potential, rest energy) Kinetic energy is the energy of a moving object mv2 KE = --------- 2 It takes ~1000 N (or ~ 225 lbs) to hit a nail and drive it 5 mm into a surface. Visit www.worldofteaching.com For 100’s of free powerpoints
Potential Energy Potential energy is a capacity of doing some work Potential energy is the energy of position Gravitational Potential Energy W = Fd = mgh = PE (potential energy) 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 PE is relative!
Rest Energy Mass 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 = m0c2 E0 (m=1 kg) = 1 kg x (3 108)2 (cm/s)2 ~ 1017 J PE (m=1 kg, h=9 km) = mgh = 1 kg x 9.8 m/s2x 9000 m ~ 105 J
Energy Transformations Many mechanical processes involve interchanges between KE, PE, and work. Energy exists in some other forms: chemical energy, heat energy, radiant energy, etc.
Conservation of Energy Energy 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
Light and Atomic Structure Light and its properties Atomic structure Interaction between Light and Matter Spectrum Chapter 5
Light is a form of energy, radiative energy Light in Everyday Life 1 Watt = 1 Joule/sec • Light has color • A prism split light into a spectrum (rainbow of colors) Light travels with a speed of c = 300,000 km/s
Interaction of Light and Matter • Emission • Absorption • Transmission (passing through) • Reflection (scattering)
Properties of Light Light behaves as both a particle and a wave Light particles are called photons, whichcan be counted individually. Light is also an electromagnetic wave The wavelength is the distance between adjacent peaks of the electric or magnetic field 1 nm (nanometer) = 10–9m1μm (micron) = 10–6 m The frequency is the number of peaks that pass by any point each second, measured in cycles per second or Hertz (Hz). light demo
Light is an electromagnetic wave Light consists of many individual photons. Each travels at the speed c and can be characterized by a wavelength and a frequency.
Many Forms of Light The spectrum of light is called the electromagnetic spectrum Different portions of the spectrum are called: The visible light - what we see with our eyes The infrared light - beyond of the red end of rainbow The ultraviolet light - beyond the blue end Radio waves - light with the longest wavelengths X rays - wavelengths shorter than ultraviolet Gamma rays - the shortest wavelength light
Electromagnetic spectrum Frequency units – Hertz 1 Hz = 1 c1
Light and Matter The amount of light is called intensity Studying spectra of celestial bodies one can learn a wealth of information about them
Atomic Structure 92 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.
Atomic Structure Positively 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.
Absorption and Emission in Gases Since 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 down The energy is emitted as a photon of light The photon has exactly the same energy that the electron has lost
Types of Spectra Emission line spectrum consists of photons emitted as each electron falls back to lower levels Absorption line spectrum appears when photons are absorbed, causing electrons to jump up in energy Each element or molecule produces its own distinct set of spectral lines
Thermal Radiation ``Complex’’ objects - planets, stars, people - produce thermal radiation Its spectrum depends only on the object’s temperature Hotter objects emit more total radiation per unit surface area The radiated energy is proportional to the fourth power of the temperature Hotter objects emit photons with a higher average energy
Reflected light When the light (for example, sunlight) strikes an object (ground, clouds, people), we see only the wavelengths of light that are reflected Different objects (fruits, rocks, atmospheric gases) reflect and absorb light at different wavelengths
The Doppler Shift Radial motion of a distant object can be determined due to the Doppler effect The Doppler effect causes shifts in the wavelengths of light If an object is moving toward us, its entire spectrum is shifted to shorter wavelengths Because shorter wavelengths of the visible light are bluer, the Doppler shift of this object is calleda blueshift The Doppler shift of a moving away object - redshift
Doppler Effect Demo Doppler effect
Summary Spectral information gives us more knowledge about the objects (composition, surface temperature, moving properties) Visible light is only a small portion of the electromagnetic spectrum The Doppler effect tells us how quickly light is moving toward or away from us
