Foundations of Physics II Definitions

• plum pudding cake
• since atom is neutral the atom must be embedded in positively charged particles
• discovered electron and measured mass-to-charge ratio

• Planetary model
• positive charge concentrated in a region
• thus positively charged nucleus is at centre with electrons orbiting it
• Problem: unstable model as electrons would eventually spiral down into nucleus

• electrons in quantized orbits
• used Planck's concept on energy quantization and applied it to electrons.

• Once an atom is in an excited state, the exited atom can make a transition back to a lower energy level, emitting a photon in the process.
• This happens without an event to trigger the transition

The interaction between the incoming photon and the atom causes the atom to return to the ground state and emit a second photon.

• coherent: individual rays of light in a laser beam maintain a fixed relationship with one another (same phase)
• monochromatic: light in a laser beam has a very narrow range of wavelengths (same frequency)
• collimated: small angle of divergence, the beam spreads out very little even over large distances.

two atoms combine in a way that one or more outer elctrons are transferred from one atom to another.

hold the molecules together by sharing the electron between two atoms

• intermolecular bond
• two molecules attracted to each other by weak electrostatic forces (van der Waals forces)
• molecule acts an an electric dipole
• 3 types: dipole-dipole force, dipole-induced dipole force and dispersion force

• responsible for water's properties (eg forms ice)
• rather weak, water changes into steam easily

• about the axis through the center of mass and perpendicular to the molecular axis:
• I=m₁r₁²+m₂r₂²

cluster of nuleons (protons and neutrons)

Nuclei with the same atomic number but different number of neutrons

The same number of neutrons but different number of protons

The same sum of protons and neutrons (but different amounts of each_

• neutrons and protons inside nucleous
• density of drop is considered uniform
• explained binding energy and radius of nucleous but didn't explain spectrum of gamma rays

• nucleons are in quantized energy levels, similar to atomic model
• this model can explain why nuclei with even Z and N are more stable and why in stable nuclei N is > Z

• spontaneous disintegration of an unstable nucleus
• 3 types: alpha, beta an dgamma

1 disintegration/s

3.7x10¹⁰ Bq

• mass and energy
• linear momentum
• angular momentum
• electric charge
• baryon number
• lepton number
• strange number