GRE Physics Exam 2 Questions
with Correct Verified Answers,
Already Passed! (Complete &
Accurate)
A student makes 10 one-second measurements
of the disintegration of a sample of a long-lived
radioactive isotope and obtains the following
values.
3, 0, 2, 1, 2, 4, 0, 1, 2, 5
How long should the student count to establish
the rate to an uncertainty of 1 percent?
(A) 80 s
(B) 160 s
(C) 2,000 s
(D) 5,000 s
(E) 6,400 s - ANS ✓No idea.
The ground state electron configuration
for phosphorus, which has 15 electrons, is
(A) 1s2 2s2 2p6 3s1 3p4
(B) 1s2 2s2 2p6 3s2 3p3
(C) 1s2 2s2 2p6 3s2 3d3
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(D) 1s2 2s2 2p6 3s1 3d4
(E) 1s2 2s2 2p6 3p2 3d3 - ANS ✓Simple chemistry and a bit of counting.
Choice (B).
The energy required to remove both electrons
from the helium atom in its ground state is
79.0 eV. How much energy is required to ionize helium (i.e., to remove
one electron) ?
(A) 24.6 eV
(B) 39.5 eV
(C) 51.8 eV
(D) 54.4 eV
(E) 65.4 eV - ANS ✓(79.0 eV)/(2^2) = 20.0 eV, which is approximately
choice (A).
The primary source of the Sun's energy is a series of thermonuclear
reactions in which the energy produced is c^2 times the mass
difference between
(A) two hydrogen atoms and one helium atom
(B) four hydrogen atoms and one helium atom
(C) six hydrogen atoms and two helium atoms
(D) three helium atoms and one carbon atom
(E) two hydrogen atoms plus two helium atoms
and one carbon atom - ANS ✓Remember this and remember it well that
there are 4 hydrogen atoms and 1 helium atom in the system of
thermonuclear reactions. Choice (B).
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In the production of X rays, the term "bremsstrahlung" refers to which
of the following?
(A) The cut-off wavelength, lmin , of the
X-ray tube
(B) The discrete X-ray lines emitted when an
electron in an outer orbit fills a vacancy in
an inner orbit of the atoms in the target
metal of the X-ray tube
(C) The discrete X-ray lines absorbed when an
electron in an inner orbit fills a vacancy in
an outer orbit of the atoms in the target
metal of the X-ray tube
(D) The smooth, continuous X-ray spectra
produced by high-energy blackbody
radiation from the X-ray tube
(E) The smooth, continuous X-ray spectra
produced by rapidly decelerating electrons
in the target metal of the X-ray tube - ANS ✓"Bremsstrahlung" tends to
involve a metal and the smooth, continuous X-ray spectra produced by
decelerating electrons. Choice (E).
In the hydrogen spectrum, the ratio of the
wavelengths for Lyman-a radiation (n = 2 to
n = 1) to Balmer-a radiation (n = 3 to n = 2) is
(A) 5/48
(B) 5/27
(C) 1/3
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(D) 3
(E) 27/5 - ANS ✓The wavelengths are less in the Lyman-alpha radiation
and in the Balmer-alpha radiation is bigger. Look for the cubed value and
get 3^3 = 27 and we spot 5/27. Choice (B).
An astronomer observes a very small moon
orbiting a planet and measures the moon's
minimum and maximum distances from the
planet's center and the moon's maximum orbital
speed. Which of the following CANNOT be
calculated from these measurements?
(A) Mass of the moon
(B) Mass of the planet
(C) Minimum speed of the moon
(D) Period of the orbit
(E) Semimajor axis of the orbit - ANS ✓The orbital influence comes from
the central body, which in this case is the planet. So the moon's mass is
purely independent of its orbital motion. Hence we get choice (A).
A particle is constrained to move in a circle with a
10-meter radius. At one instant, the particle's
speed is 10 meters per second and is increasing at a rate of 10 meters
per second squared. The angle between the particle's velocity and
acceleration vectors is
(A) 0∞
(B) 30∞
(C) 45∞
(D) 60∞
GRE Physics Exam
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