Wave • Wave: a rythmic disturbance in both time and space. • Waves transfer energy not matter.
Amplitude: The distance from the equilibrium (baseline) to the crest or trough) l
Speed of a Wave v =lf v speed l wavelength f frequency
Speed of a Wave v= d/t v = l/T v =lf
Transverse Waves The particles vibrate perpendicular to the direction of the wave's propagation (ex: waves along a string, electromagnetic waves).
Longitudinal Waves • The particle displacement is parallel to the direction of wave propagation (ex: sound)
Elliptical Waves Result when longitudinal and transverse waves are superpositioned. (ex: surface water waves)
Torsional Waves • Video link on Web • http://www.youtube.com/watch?v=P0Fi1VcbpAI
Wave Categories • MechanicalWaves: require a medium. Examples: • Water waves( Tsunami) • Sound waves (f=20-20000 hertz, v= 340 m/sec in air but varies for different media, faster in solids) • Earthquake waves • ElectromagneticWaves: do not require a medium. Can travel through space (vacuum). Example: Light from the sun reaches us Note: all EM waves have a speed through vacuum of 3 x 108 m/sec.
Electromagnetic Waves Type of radiation Wavelengths(m) Radio 570 - 2.8 TV 5.6 - 0.34 Microwave 0.1 - 0.001 Infrared radiation 10-3 - 10-7 visible light red 700x10-9 (700nm) orange yellow green blue indigo violet 400x10-9 (400nm) ultraviolet 10-7 - 10-10 x-rays 10-10 -10-12 gamma rays shorter than 10-12
Note • A wave’s speed is constant in a given medium. If you change the frequency of the wave, the wavelength will also change. If the frequency increases, the wavelength will decrease. • When a wave travels from one medium to a different medium, the frequency remains the same and the speed changes.
Problem • What is the frequency of a light wave of wave length 550x 10-9 m? • What color light is it?
Electrons orbit the nucleus in circular paths of fixed energy (energy levels). Niels Bohr’s Atomic Model (1913)
Niels Bohr’s Atom Cont’d • Electrons can jump from energy level to energy level. • Electrons absorb or emit light energy when they jump from one energy level to another.
Hydrogen Emission Spectrum Violet 410nm Blue 434nm Blue-Green 486 nm Red 656nm Balmer Series