Waves
Wave – periodic disturbance of a medium from an equilibrium
condition that travels through space
Possible Media
• water
• air (sound)
• solids (earthquake)
Wave Properties
Velocity (v) – speed at which the wave moves
Wavelength (λ) – distance over which a wave repeats
Frequency (f) – number of waves that pass by a given point every
second (waves/second = Hertz {Hz})
v = "#f
Light: Classical Model
Maxwell’s Equations
• light is a continuous wave of Electromagnetic (EM) Radiation
• moves at a constant speed (c = 300,000 km/s = 186,000 miles/sec)
c = "#f
• EM Radiation does NOT require a medium
Field Theory
Electric Field
Magnetic Field
Electromagnetic Spectrum
A photon with a small wavelength has high energy & high frequency
Light: Quantum Mechanics Model
What part of a wave determines the amount of energy?
Wave model: larger amplitude = greater energy
Photoelectric Effect – light shining on certain materials (e.g. silicon)
will generate electricity
Discovery 1: increasing intensity of the light bulb increased the
number of electrons released but not the energy
Discovery 2: changing the color (i.e. wavelength) of light changes
the energy; shorter λ light = higher energy
E photon
1240
=
"
λ measured in nm
E measured in “electron-Volts”
1 eV = 1.60 x 10-19 J
Reflection – the “bouncing” of light off of surfaces
Law of Reflection: Reflected angle = Incident angle
Air
Glass
Refraction – the “bending” of light as it passes from one
medium to another
Matter
Atoms (“indivisible”)
• 3 parts: protons, neutrons, electrons
nucleus
(p+) (no) (e-)
Atomic Number = # of protons in nucleus (defines element)
Each element can be found in different varieties (Isotopes)
Bohr Model
Binding Energy – energy required to keep an electron in its orbit
around the nucleus (depends on orbit size)
Neils Bohr discovered that electrons need to orbit the nucleus
with specific amounts of binding energy
Nucleus
• In other words, e- orbits can only be of certain sizes
• Orbit sizes are determined by the number of p+ in the nucleus
Atomic States
Ground State – when all electrons occupy all orbits closest
to the nucleus (occurs at low temperatures)
H
H
H
Excited State – electron(s) occupy any orbit beyond the
ground state (occurs at moderate temperatures)
Ionized State – electron(s) removed from the atom after
absorbing too much energy (occurs at high temperatures)
Chemical Bonds
Two (or more) atoms can form new substances by bonding to each
other by sharing electrons (covalent) or exchanging electrons (ionic).
H
O
C
Molecule – two or more atoms chemically bonded
H2
N
O2
Compound – molecules made of two or more elements
NH3 (ammonia)
H2O
Organic Molecule – molecules that contain carbon chains (life)
C4 H 8
Temperature
Measurement of the average energy of atoms within a substance
Low energy = Cold
High energy = Hot
Energy of the atoms or molecules is increased with the absorption
of light or by increasing pressure
States of Matter:
Matter will change states based on temperature (pressure)