Equations for the first exam:
Motion:
Kepler's laws:
1) all orbits are ellipses with the Sun at one focus.
2) Orbits sweep out equal area in equal time.
(Within a given orbit, the planet slows down as it gets farther from the
Sun.)
3) P2 = a3
(P is the time the planet takes to complete an orbit, and
a is the semimajor axis of the orbit. This formula means that the
large orbits take a very long time to get around, so the planets on
large orbits must be moving more slowly.)
Newton's laws:
A=F/m
(A is acceleration, F is total force, usually gravity, and m is the
mass of the object that is accelerating.)
force of gravity F = GMm/d2
(where G is a constant that is of no consequence to our purposes, M is
one of the masses, m is the other mass, and d is the distance between
the centers of the two masses involved in the action/reaction pair
force of gravity we are talking about)
Rules of light:
Thermal emission depends only on temperature T, and the total rate that energy
is emitted into light (also called "radiation") is proportional to T4.
The average energy per photon, which is also the average frequency of the light
waves, is proportional to T. For T=6000 K like the surface of the Sun, this
means the average frequency is visible light. For T=300 K, like in this room,
the average frequence is infrared.
Spectral lines:
Atoms absorb and emit light only at the special energies where a photon can
have a frequency (equal to the photon energy divided by Planck's constant h)
that "resonates" (experiences constructive interference, like the note on a
guitar string) inside the atom. This is different energies for different types
of atoms, so the "lines" they absorb and emit provide a signature of the type
of atom. That's how we know the Sun is mostly hydrogen with about 25% helium by mass.
Wave mechanics:
Waves are governed by interference, and they appear to in some sense "tell the photons
where to go." Interference can produce refraction and reflection, both useful in
focusing light and creating images, and it can produce diffraction, which is a blurring
of images that come through an aperture. But diffraction is not all bad, because by
carefully creating tiny slits, we can control diffraction so that it sends different
colors (frequencies) of light to different places, creating a "spectrum." Such careful
slits are called a "diffraction grating," and they work better than prisms (which us
refraction like how raindrops create rainbows) for creating spectra.