Physics - Atoms Molecules and Nuclei Question Paper 1
Exam Duration: 45 Mins Total Questions : 30
Alpha particles that come closer to nuclei
- (a)
are deflected more
- (b)
are deflected less
- (c)
are slowed down more
- (d)
make more collisions with nuclei
The size of atom is nearly equal to
- (a)
1 nm
- (b)
1 micron
- (c)
\(1\dot { A } \)
- (d)
1 fermi
The ionisation energy of hydrogen is 13.6 eV. Following Bohr's theory, the energy corresponding to a transition between the 3rd and the 4th orbit is
- (a)
3.4 eV
- (b)
1.51 eV
- (c)
0.85 eV
- (d)
0.66 eV
Hydrogen atoms are excited from ground state of the principal quantum number 4. Then the number of spectral lines observed will be
- (a)
3
- (b)
6
- (c)
5
- (d)
2
Minimum excitation potential of Bohr's first orbit in hydrogen atom is
- (a)
13.6 eV
- (b)
3.4 eV
- (c)
10.2 eV
- (d)
3.6 eV
If r1 and r2 are the radii of nuclei of mass number 64 and 27 respectively, then ratio (r1/r2) is
- (a)
64/27
- (b)
27/64
- (c)
4/3
- (d)
1
The ratio of longest wavelength and shortest wavelength observed in the five spectral series of emission spectrum of hydrogen is
- (a)
\(\frac { 4 }{ 3 } \)
- (b)
\(\frac { 525 }{ 376 } \)
- (c)
25
- (d)
\(\frac { 960 }{ 11 } \)
Hydrogen atom emits blue light when it changes from n = 4 energy level to the n =2 level. Which colour of light would the atom emit when it changes from the n =5 to the n = 2 level?
- (a)
Red
- (b)
Yellow
- (c)
Green
- (d)
Violet
Of the following transitions in hydrogen atom, the one which gives an absorption line of lowest frequency is
- (a)
n = 1 to n = 2
- (b)
n = 3 to n =8
- (c)
n = 2 to n = 1
- (d)
n = 8 to n = 3
Rydberg is unit of
- (a)
wavelength
- (b)
wave number
- (c)
energy
- (d)
a universal constant called Rydberg constant
The binding energy per nucleon of \({ Li }^{ 7 }\)and \({ He }^{ 4 }\) are 5.6 MeV and 7.06 Mev respectively, Then the energy of the reaction : \({ Li }^{ 7 }\)+ P = \(2[_{ 2 }{ He }^{ 4 }]\) is
- (a)
17.28 MeV
- (b)
39.2 MeV
- (c)
28.24 MeV
- (d)
1.46 MeV
A \(\beta \)- particle is emitted by a radioactive nucleus at the time of conversion of
- (a)
a neutron into a proton
- (b)
a proton into a neutron
- (c)
a nucleon into energy
- (d)
a positron into energy
Maximum penetrating power is that of
- (a)
\(\alpha \)-rays
- (b)
\(\beta \)-rays
- (c)
\(\gamma \)-rays
- (d)
X - rays
Electron emitted in beta radiation originates from
- (a)
inner orbits
- (b)
free electrons existing in nuclei
- (c)
decay of neutron in a nucleus
- (d)
photon escaping from the nucleus
Which of the following nuclei is more easily fissionable by slow moving neutrons?
- (a)
U233
- (b)
U235
- (c)
U238
- (d)
Pu239
A radioactive material decays by simultaneous emission of two particles with respective half lives 1620 and 810 years. The time in years after which one-fourth of the material remains is
- (a)
1080
- (b)
2430
- (c)
3240
- (d)
4860
Let mp be the mass of a proton, mn the mass of neutron, M1 the mass of 10Ne20 nucleus and M2, the mass of a 20Ca40 nucleus, Then
- (a)
M2 = 2M1
- (b)
M2 > 2M1
- (c)
M2 < 2M1 and M1(mn+mp)
- (d)
M1 > (mn+mp) but M2 < 2M1
A radioactive sample consists of two distinct species having equal number of atoms initially. The mean life time of one species is \(\tau \) and that of the other is \(5\tau \). The decay produces in both cases are stable. A plot is made of the total number of radio-active nuclei as a function of time. Which of the following figures best represents the form of this plot?
- (a)
- (b)
- (c)
- (d)
It is possible to understand nuclear fission on the basis of the
- (a)
meson theory of the nuclear forces
- (b)
proton-proton cycle
- (c)
independent particle model of the nucleus
- (d)
liquid drop model of the nucleus
The magnitude of angular momentum, orbit radius and frequency of revolution of electron in hydrogen atom corresponding to quantum number n are L, r and f respectively. Then, according to Bohr's theory of hydrogen atom
- (a)
fr2L is constant for all orbits
- (b)
frL is constant for all orbits
- (c)
f2rL is constant for all orbits
- (d)
frL2 is constant or all orbits
If electron and proton are bound by gravitational attraction only, then size of the Bohr's first orbit is
- (a)
1040 time smaller than its actual value
- (b)
remains same
- (c)
about twice the size of actual orbit
- (d)
greater than the size of universe
In a hypothetical system, a particle of mass m and charge -3q is moving around a very heavy particle having charge q. Assuming Bohr's model to be true to this system, the orbital velocity of mass m when it nearest to heavy particle is
- (a)
\(3q^2\over 2\epsilon_oh\)
- (b)
\(3q^2\over 4\epsilon_oh\)
- (c)
\(3q\over 2\epsilon_o h\)
- (d)
\(3q\over 4\epsilon_o h\)
The angular momentum of an electron in the hydrogen atom is \(3h\over 2\pi\). Here h is Planck's constant. The kinetic energy of this electron is
- (a)
4.53 eV
- (b)
1.51 eV
- (c)
3.4 eV
- (d)
6.8 eV
In hydrogen and hydrogen like atoms, the ratio of differene of energies E4n-E2n and E2n-En varies with its atomic number Z and n as
- (a)
\(Z^2\over n^2\)
- (b)
\(Z^4\over n^4\)
- (c)
\(Z\over n\)
- (d)
Z0n0
If the electron in a hydrogen atom were in the energy level with n=3, then how much energy would be required to ionise the atom (ionisation energy of H-atom is 2.18X10-18J)?
- (a)
6.54X10-19J
- (b)
1.43X10-19J
- (c)
2.42X10-19J
- (d)
3.14X10-19J
Consider the spectral line resulting from the transition n=2\(\rightarrow\)n=1 in the atoms and ions given below. The shortest wavelength is produced by
- (a)
hydrogen atom
- (b)
deuterium atom
- (c)
singly ionised helium
- (d)
doubly ionised lithium
If radiation of all wavelengths from ultraviolet to infrared is passed through hydrogen gas at room temperature, then absorption lines will be observed in the
- (a)
Lyman series
- (b)
Balmer series
- (c)
Both (a) and (b)
- (d)
Neither (a) nor (b)
Two H-atoms in the ground state collide inelastically. The maximum amount by which their combined kinetic energy is reduced is
- (a)
10.20 eV
- (b)
20.40 eV
- (c)
13.6 eV
- (d)
27.2 eV
The electron in hydrogen atom in a sample is in nth excited state, then the number of different spectrum lines obtained in its emission spectrum will be
- (a)
1+2+3+....+(n-1)
- (b)
1+2+3+....+(n)
- (c)
1+2+3+...+(n+1)
- (d)
1X2X3X....X(n-1)
A diatomic molecule is made of two masses m1 and m2 which are separated by a distance r. If we calculate its rotational energy by applying Bohr's rule of angular momentum quantization, its energy will be given by (n is an integer)
- (a)
\({(m_1+m_2)^2n^2h^2}\over {2m_1^2m_2^2r^2}\)
- (b)
\(n^2h^2\over2(m_1+m_2)r^2\)
- (c)
\(2n^2h^2\over (m_1+m_2)r^2\)
- (d)
\((m_1+m_2)n^2h^2\over2m_1m_2r^2\)
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