Light, Energy and Waves
Transverse waves: Wave Types Waves in which the medium moves at right angles to the direction of the wave
Compressional (or longitudinal) waves Waves in which the medium moves back and forth in the same direction as the wave
Amplitude: height of a wave (intensity) Wavelength: distance between crests (λ) Frequency: number of wavelengths passing a point in a given amount of time (cycles/ sec., Hz) (ν) Speed: light ( 3.00 X 10 8 m/s = c)
What two stations are on the radio?? AM and FM What do you think those stand for?? Amplitude Modulation and Frequency Modulation
As you get older and older, your ears are not able to hear higher frequencies. How good are your ears? http://www.cleanvideosearch.com/media/action /yt/watch?videoid=h-iczelj8m0 Let s try it again http://www.cleanvideosearch.com/media/action /yt/watch?videoid=h5l4rt4ol7m
The change in the frequency of a sound caused by the motion of either the listener or the source of the sound. The high frequency gives off the sound as a high pitch as it approaches us and a low pitch as it goes away.
If the source of the sound is moving as fast or faster than the speed of sound, the sound waves will pile up into a shock wave. Sonic boom! Sounds very much like an explosion. http://www.cleanvideosearch.co m/media/action/yt/watch?videoid =BHBevPYVzaY
Can sound waves really shatter a wine glass? Yes, if the frequency of the sound matches the natural frequency of the glass, and if the amplitude is sufficient. The glass s natural frequency can be determined by flicking the glass with your finger and listening to the tone it makes. If the glass is being bombarded by sound waves of this frequency, the amplitude of the vibrating glass with grow and grow until the glass shatters. Demo Anyone can do it
Electromagnetic radiation 1. light 2. x-rays 3. gamma rays 4. radio waves
Light behaves as both a wave and a particle Photon: an amount of light that carries energy. Energy of a photon is high when the frequency is high higher frequency is more dangerous low frequency is not dangerous
Remember that different wavelengths of light carry different amounts of energy per photon Ex: red light (longer wavelength) has lower energy photons than blue light When elements are given some energy, the electrons go to a higher state and then drop back down When they drop back down, they give off energy in photons
Planck proposed that a fixed amount of energy can be absorbed or emitted by atoms, and called the energy a quantum E = hc = hv λ v the frequency of wave h = 6.63 x 10-34 Hz (Planck s constant) c = 3 x 10 8 m/s (speed of light) λ wavelength of wave
Calculate the energy of photons of radiation whose frequency is 5.00 10 14 Hz. E = hv E = 6.63 x 10-34 Hz (5.00 10 14 ) Ultraviolet radiation has a frequency of 6.8 10 15 Hz. Calculate the energy of the photon. A sodium vapor lamp emits light photons with a wavelength of 5.89 10-7 m. What is the energy of these photons?
Atoms of a given element with: same #protons but different # neutrons
Isotopes of certain unstable elements that spontaneously emit particles and energy from the nucleus. Henri Beckerel 1896 accidentally observed radioactivity of uranium salts that were fogging photographic film. His associates were Marie and Pierre Curie.
Emission of alpha particles a : helium nuclei two protons and two neutrons charge +2e can travel a few inches through air can be stopped by a sheet of paper, clothing.
Uranium Thorium
http://education.jlab.org/glossary/alphadecay.gif
Beta particles b: electrons ejected from the nucleus when neutrons decay Beta particles have the same charge and mass as "normal" electrons. Can be stopped by aluminum foil or a block of wood.
Gamma radiation g : electromagnetic energy that is released. Gamma rays are electromagnetic waves. They have no mass. Gamma radiation has no charge. Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead.
Alpha Beta Gamma
The time for half of the radioactive nuclei in a given sample to undergo decay.
Isotope Half-Life Radiation Emitted Carbon-14 5,730 years b, g Radon-222 3.8 days a Uranium-235 7.0 x 10 8 years Uranium-238 4.46 x 10 9 years a, g a
After one half life there is 1/2 of original sample left. After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.
A
You have 100 g of radioactive C-14. The halflife of C-14 is 5730 years. How many grams are left after one half-life? Answer:50 g How many grams are left after two half-lives?
A sample of 3x10 7 Radon atoms are trapped in a basement that is sealed. The half-life of Radon is 3.83 days. How many radon atoms are left after 31 days? A = A 0 x (.5) n A = A 0 x (.5) n n = 31/3.83 = 8.09 n = number of half lives A = 3 x 10 7 x (.5) 8.09
The half-life of Zn-71 is 2.4 minutes. If you had 100.0 g at the beginning, how many grams would be left after 7.2 minutes has elapsed?