Waves type of disturbance that can propagate or travel. wavelle lnlgth ( ) crest amplitude (A) velocity (v) trough Wavelength ( is a distance, so its units are m, cm, or mm, etc. Period (T): time between crest (or trough) passages Frequency ( ): rate of passage of crests (or troughs c= (units: Hertz or cycles/sec) Equilibrium position
Shorter wavelength ( ) = higher frequency ( ) and therefore higher energy
Waves bend when they pass through material of different densities. swimming pool air water prism air glass Refraction
All radiation (including visible light) travels as Electromagnetic waves. Examples of objects with magnetic fields: Magnet the Earth the Sun Examples of objects with electric fields: Electrical appliances Lightning Protons, electrons
Electromagnetic Radiation How we get information about the cosmos e.g. Visible Light
c = 1 nm = 10 -9 m, 1 Angstrom = 10 -10 m The Electromagnetic Spectrum
When you bend light, bending angle depends on wavelength, or color. Refraction of light (Prism demo)
Types of Spectra 1. "Continuous" spectrum luminous solid, liquid, or dense gas, emits light of all wavelengths, produces a continuous spectrum 2. "Emission" spectrum low-density, hot gas emits light whose spectrum consists of a series of bright emission lines that are characteristic of the composition of the gas. 1."Absorption” Spectrum c ool, thin gas absorbs certain wavelengths from a continuous spectrum, leaving dark absorption lines in their place, superimposed on the continuous spectrum.
Pattern of lines is a fingerprint of the element
For a given element, emission and absorption lines occur at the same wavelengths. Sodium emission and absorption spectra
The Particle Nature of Light Light interacts with matter as individual packets of energy, called photons. photon energy is proportional to frequency: example: ultraviolet photons are more dangerous than visible photons.
The Nature of Atoms The Bohr model of the Hydrogen atom: _ + proton electron "ground state" _ + "excited state"
When an atom absorbs a photon, it moves to a higher energy state briefly When it jumps back to lower energy state, it emits photon(s) in a random direction, conserving the total energy of the system
Other elements Helium Carbon neutron proton Each element has its own allowed energy levels yielding a unique spectral fingerprint.