PHYS 1260 EXAM 4 QUESTIONS
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Why is a larger nucleus generally less stable than a smaller nucleus? -
ANSWER Because the strong force is short range, protons in a large
nucleus are farther apart on...
Why is a larger nucleus generally less stable than a smaller nucleus? -
ANSWER ✔ Because the strong force is short range, protons in a large
nucleus are farther apart on average than in a small nucleus, and the
strong force is less effective between wide-apart protons.
length contraction - ANSWER ✔ - as objects move through spacetime,
space as well as time changes
- space is contracted, making the objects look shorter when they move
by us at relativistic spds
- L = L0 * sqrt (1 - (v^2/c^2))
- length contraction takes place only in the direction of travel = if an
object is traveling horizontally, no contraction takes place vertically
mass, energy, and E = mc^2 - ANSWER ✔ - a piece of matter, even at
rest and not interacting w/ anything else, has an "energy of being" = rest
energy
- Einstein concluded that it takes energy to make mass and that energy is
released if mass disappears
- the amount of energy E is related to the amount of mass m by: E =
mc^2
,- saying that a power plant delivers 90 mil megajoules of energy to its
consumers is equivalent to saying that it delivers 1 gram of energy to its
consumers, bc mass and energy are equivalent
- in 1 sec, 4.5 mil tons of mass are converted to radiant energy in the
sun; the sun is so massive, however, that in 1 mil years only 1 ten-
millionth of the sun's mass will have been converted to radiant energy
correspondence principle - ANSWER ✔ - it states that any new theory
or any new description of nature must agree w/ the old where the old
gives correct results
- if the equations of special relativity are valid, they must correspond to
those of classical mechanics when spds much less than the spd of light
are considered
- when spds are very low, compared to the spd of light v is much smaller
than c, then:
y = 1/sqrt(1-(v^2/c^2)) = 1/sqrt(1-0) = 1
light emission - ANSWER ✔ - light emission is understood in terms of
familiar planetary model of the atom
- just as each element is characterized by the # of e- that occupy the
shells surrounding its atomic nucleus, each element also possess its own
characteristics pattern of electron shells, or energy states
excitation - ANSWER ✔ - when energy is imparted to an element, an
electron may be boosted to a higher energy level --> this atom is said to
be excited
- the frequency of an emitted photon ~ energy level difference in de-
exciting --> E = hf
which has less energy per photon? - ANSWER ✔ red light --> in accord
w/ E ~ f, the lowest-frequency light has the lowest energy per photon
excitation is the process in which - ANSWER ✔ electrons are boosted
to higher energy levels in an atom
, emission spectra - ANSWER ✔ - spectroscope = arrangment of slit,
focusing lenses, and prism or diffraction grating; to see emission
spectrum of light from glowing element; when an electron is at a higher
energy level, atom is excited and temporarily loses the acquired energy
when it returns to a lower level and emits radiant energy
- spectral lines = forms an image of the slit on the screen using a
spectroscope; each component of color is focused at a definite position
according to frequency
- spectral lines of hydrogen - more orderly than other elements;
successive lines get closer until the lines merge; swedish physicist and
mathematician Johannes Rydberg discovered that the sum of the
frequencies of 2 lines often equals the frequency of a 3rd line
- Ritz combination principle = Rydberg's discovery called the Ritz
combination principle = the spectral lines of any element include
frequencies that are either the sum or the difference of the frequencies of
2 other lines
most of what we know about atoms is gained by investigating the -
ANSWER ✔ light they emit --> light emitted by atoms, their atomic
spectra are considered to be the fingerprints of atoms
uncertainty principle - ANSWER ✔ - act of observing something as tiny
as an electron probes the e- and, in doing so, produces a considerable
uncertainty in either its position or its motion
- german physicists Werner Heisenberg called this the uncertainty
principle
- when the uncertainties the measurements of momentum p and position
x for a particle are multiplied together, the product must be equal to or
greater than Planck's constant, h, divided by 2pi, which is represented as
h (called h-bar) ΔpΔx ≥ ħ
- the Δ is "uncertainty in measurement of": Δp is uncertainty in
measurement of p and Δx the uncertainty in position. the product of
uncertainties must be equal to or greater than (≥) the size of ħ
, - applies to uncertainties of measurements of energy and time. the
uncertainty in knowledge of energy, ΔE, and the duration taken to
measure the energy, Δt, are related by the expression: ΔEΔt ≥ ħ.
- Heisenberg's uncertainty principle applies only to quantum mechanics;
does not apply to: uncertainties of macroscopic lab measurements; a
shield of nature's secrets; the notion that science is basically uncertain
What is the role of neutrons in the atomic nucleus? - ANSWER ✔ To
reduce electrostatic repulsion
Which contains the higher percentage of neutrons: large nuclei or small
nuclei? - ANSWER ✔ Large nuclei contain a larger percentage of
neutrons.
How does the rate of decay of a long-half-life material normally
compare with the rate of decay of a short-halflife material? - ANSWER
✔ The rate of decay is lower for a long-half-life material. Half life ~ the
decay rate. Longer the half life, the slower the rate.
What is the half-life of Ra-226? - ANSWER ✔ The half-life of Ra-226
is 1620 years.
What occurs when a nitrogen nucleus captures an extra neutron? -
ANSWER ✔ neutron activation
Which is more prevalent in the food we eat: carbon-12 or carbon-14? -
ANSWER ✔ Most of the carbon we ingest is carbon-12.
Why is lead found in all deposits of uranium ore? - ANSWER ✔ Lead
is the end product in the radioactive decay process of uranium.
Which radiation has no electric charge associated with it? - ANSWER
✔ Gamma
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