ΠΡΟΣΟΧΗ ΤΑ ΠΑΡΑΚΑΤΩ 15 ΘΕΜΑΤΑ ΔΕΝ ΕΙΝΑΙ ΣΟΣ ΓΙΑ ΤΙΣ ΠΑΝΕΛΛΗΝΙΕΣ / ΠΑΝΕΛΛΑΔΙΚΕΣ ΕΞΕΤΑΣΕΙΣ ΚΑΠΟΙΑ ΕΙΝΑΙ ΛΙΓΟ ΔΥΣΚΟΛΑ ΕΝΩ ΣΤΟ ΤΕΛΟΣ ΕΧΟΥΜΕ ΒΑΛΕΙ ΚΑΙ ΜΕΡΙΚΑ ΕΥΚΟΛΑ
ΕΙΝΑΙ ΣΤΑ ΑΓΓΛΙΚΑ ΓΙΑΤΙ ΕΧΟΥΝ ΜΠΕΙ ΣΑΝ ΘΕΜΑΤΑ ΣΕ ΕΞΕΤΑΣΕΙΣ ΣΕ ΒΡΕΤΑΝΙΚΑ ή ΑΜΕΡΙΚΑΝΙΚΑ ΠΑΝΕΠΙΣΤΗΜΙΑ
1. In the production of X rays, the term
“bremsstrahlung” refers to which of the
(A) The cut-off wavelength, λmin, of the
(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
2. Positronium is an atom formed by an electron
and a positron (antielectron). It is similar to the
hydrogen atom, with the positron replacing the
proton. If a positronium atom makes a transition
from the state with n = 3 to a state with n = 1,
the energy of the photon emitted in this transition
is closest to
(A) 6.0 eV
(B) 6.8 eV
(C) 12.2 eV
(D) 13.6 eV
(E) 24.2 eV
3. A sample of radioactive nuclei of a certain element
can decay only by g -emission and b -emission. If
the half-life for g -emission is 24 minutes and that
for b -emission is 36 minutes, the half-life for the
(A) 30 minutes
(B) 24 minutes
(C) 20.8 minutes
(D) 14.4 minutes
(E) 6 minutes
4. Electromagnetic radiation provides a means to
probe aspects of the physical universe. Which
of the following statements regarding radiation
spectra is NOT correct?
(A) Lines in the infrared, visible, and ultraviolet
regions of the spectrum reveal primarily the
nuclear structure of the sample.
(B) The wavelengths identified in an absorption
spectrum of an element are among those in
its emission spectrum.
(C) Absorption spectra can be used to determine
which elements are present in distant stars.
(D) Spectral analysis can be used to identify the
composition of galactic dust.
(E) Band spectra are due to molecules.
5. The 238U nucleus has a binding energy of about
7.6 MeV per nucleon. If the nucleus were to
fission into two equal fragments, each would have
a kinetic energy of just over 100 MeV. From this,
it can be concluded that
(A) 238U cannot fission spontaneously
(B) 238U has a large neutron excess
(C) nuclei near A = 120 have masses greater than
half that of 238U
(D) nuclei near A = 120 must be bound by about
(E) nuclei near A = 120 must be bound by about
6. When Ζ=4
Α=7 Be transforms into Ζ=3
Α=7 Li, it does so by
(A) emitting an alpha particle only
(B) emitting an electron only
(C) emitting a neutron only
(D) emitting a positron only
(E) electron capture by the nucleus with emission
of a neutrino
7. The Bragg experiment used X-rays to investigate crystal structure.
Which statement best describes the results of this experiment?
(A) X-rays are scattered from a crystal and form an interference pattern.
(B) X-rays penetrate a crystal and form an interference pattern behind it.
(C) X-rays are absorbed and re-emitted equally in all directions by a crystal.
(D) X-rays absorbed by a crystal produce minima and those reflected produce maxima.
8. Hospital patients are sometimes injected with radioactive tracers.
The purpose of a radioactive tracer is . . .
1 to identify the patient’s blood group.
2 to sedate the patient before an operation.
3 to track the movement of substances in the patient’s body.
4 to track the patient’s movements in the hospital.
9. Which of the following is the most suitable radioactive substance to use as a tracer?
1 a gamma emitter with a long half-life
2 a gamma emitter with a short half-life
3 an alpha emitter with a long half-life
4 an alpha emitter with a short half-life
10. Which of the following statements is correct for gamma radiation?
1 It is a stream of electrons.
2 It is a stream of protons.
3 It is deflected by an electric field.
4 It is not deflected by a magnetic field.
11. Which description is correct for the nucleus of a medium-sized atom?
It is a group of . . .
1 electrons and neutrons.
2 electrons, neutrons and protons.
3 electrons and protons.
4 neutrons and protons.
12. An example of something which can be dated by using carbon-14 measurements is . . .
1 a copper coin.
2 a gold brooch.
3 a leather belt.
4 an iron horseshoe.
13. A sample of charcoal from the Stone Age campfire contains 12 billion carbon-14 atoms.
Approximately how many carbon-14 atoms would the sample have contained 6000 years ago?
1 16 billion
2 12 billion
3 24 billion
4 48 billion
14. Carbon-14 cannot be used to date samples more than 45 000 years old.
Four students discuss this.
Which student, 1, 2, 3 or 4, has the correct explanation?
1 ‘It will take too long to make the measurements.’
2 ‘No carbon-14 atoms will be left in the specimen.’
3 ‘The proportion of carbon-14 atoms will be too small to measure.’
4 ‘There are no samples more than 45 000 years old.’
15. A beta (β) particle from an atom of carbon-14 is . . .
1 an electron from the inner part (nucleus) of the atom.
2 an electron from the outer part of the atom.
3 a helium nucleus.
4 a neutron.
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