INDIAN SCHOOL MUSCAT
CLASS : XII Physics Worksheet 7 (2014-2015)
Dual nature of radiation & matter, Nuclei & Atoms
Section A .Conceptual and Application Type Questions
1. Energy levels A, B, C of a certain atom correspond to increasing values of energy (i.e.,) EA < EB < EC. If
λ1, λ2, λ3 are the wavelengths of radiations corresponding to the transitions C to B, B to A and C to A
respectively, which of the following statements is correct.
2. The first excitation potential energy or the minimum energy required to excite the atom from
ground state of hydrogen atom is, (a) 13.6 eV (b) 10.2eV (c) 3.4 eV (d) 1.89 eV .
3. From the relation R = R0A1/3, where R0 is a constant and A is the mass number of a nucleus, show
that the nuclear matter density is nearly constant (i.e. independent of A).
4.For a given kinetic energy ,which of the following has the smallest de Broglie wavelength;
elctron,proton, α particle?
5.Are matter waves electromagnetic waves ?.
6.Name physical quantity whose dimensions are same as Planck’s constant.
7.On a certain photosensitive material green wavelength produces emission of electrons whereas
orange does not produce . Which of the following wavelengths i) blue ii) red can produce emission of
electron from the same material ? Justify.
8.What is the momentum of a photon of i) frequency ν ii) wavelength λ?
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9.An electron and photon have same deBroglie wave length of 10-10m. Which of the two has greater
kinetic energy?
10.An α- particle and a proton are accelerated from rest through the same potential difference V.Find
the ratio of their de Broglie wave length.
11. A proton and an electron have same deBroglie wavelength .Which of them moves faster and
possesses more kinetic energy ? Justify.
12. What exactly makes large nuclei unstable ?
13. select the pairs of isobars,isotones from the following.
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13
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6C ,7N ,7N ,8O
14. Among the two nucleids 3X7, 3Y4,which one of them is likely to be more stable. Justify.
15. Explain whether the neutron proton ratio increases or decreases during i) β+ decay ii) β- decay. ?
16.Define Q-value of a nuclear reaction.
Section B Numerical problems
1. Find the (a) maximum frequency, and (b) minimum wavelength of X-rays produced by 30 kV electrons.
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2. The work function of Caesium metal is 2.14 eV. When light of frequency 6 ×10 Hz is incident on the
metal surface, photo emission of electrons occurs. What is the (a) maximum kinetic energy of the
emitted electrons, (b) Stopping potential, and (c) maximum speed of the emitted photoelectrons?
3. The photoelectric cut-off voltage in a certain experiment is 1.5 V. What is the maximum kinetic energy
of photoelectrons emitted?
4. In an experiment on photoelectric effect, the slope of the cut-off voltage versus frequency of incident
light is found to be 4.12 × 10–15 V s. Calculate the value of Planck’s constant.
5. Calculate the (a) momentum, and (b) de Broglie wavelength of the electrons accelerated through a
potential difference of 56 V.
6. The wavelength of light from the spectral emission line of sodium is 589 nm. Find the kinetic energy
at which (a) an electron, and (b) a neutron, would have the same de Broglie wavelength.
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7. What is the shortest wavelength present in the Paschen series of spectral lines?
8. The ground state energy of hydrogen atom is –13.6 eV. What are the kinetic and potential energies
of the electron in this state?
9. (a) Using the Bohr’s model calculate the speed of the electron in a hydrogen atom in the n = 1, 2, and
3 levels. (b) Calculate the orbital period in each of these levels.
10. Wavelength of Balmer first line is 6563Å. Calculate the wavelength of second line.
11. A radioactive isotope has a half-life of T years. How long will it take the activity to reduce to
a) 3.125%, b) 1% of its original value?
12. The work function of Iron is 4.7eV. Calculate the cut off frequency and the corresponding cut off
wave length for this metal.
13. The mass numbers of two nuclei P and Q are 8, 27 respectively, find the ratio of their nuclear radii
and density.
14. The binding energy per nucleon for 6C12 nucleus is 7.68 MeV and that for 6C13 is 7.47 MeV.
Calculate the energy required to remove a neutron from 6C13 nucleus.
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15. The half-life of 84Po
is 3 minute. What percentage of the sample has decayed in 15 minutes?
16. Calculate the radius of 13Al27 nucleus.
17. Tritium has a half life of 12.5 years. What fraction of the sample of will be left over after 25 years?
18. What is the de Broglie wavelength associted with an electron accelearted through a potential of
100 V ?
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