Physics - Atoms Molecules and Nuclei
Exam Duration: 45 Mins Total Questions : 30
In Rutherford's experiment, silver foil is replaced by a copper foil of the same thickness. The number of alpha particles scattered through the same angle per minute in copper foil is proportional to
- (a)
\(\frac { { Z }_{ Cu } }{ { Z }_{ Ag } } \)
- (b)
\({ \left( \frac { { Z }_{ Cu } }{ { Z }_{ Ag } } \right) }^{ 2 }\)
- (c)
\(\frac { { Z }_{ Ag } }{ { Z }_{ Cu } } \)
- (d)
\({ \left( \frac { { Z }_{ Ag } }{ { Z }_{ Cu } } \right) }^{ 2 }\)
What is the radius of Iodine atom (atomic number 53, mass number 126)?
- (a)
\(2.5\times { 10 }^{ -11 }m\)
- (b)
\(2.5\times { 10 }^{ -9 }m\)
- (c)
\(7\times { 10 }^{ -9 }m\)
- (d)
\(7\times { 10 }^{ -6 }m\)
Radius of first Bohr orbit is 'r'. The radius of second Bohr orbit is
- (a)
4r
- (b)
2r
- (c)
8r
- (d)
\(2\sqrt { 2 } r\)
The order of energies of energy levels A, B and C is \({ E }_{ A }<{ E }_{ B }<{ E }_{ C }\). If the wavelength corresponding to transitions \(C\longrightarrow B,\quad B\longrightarrow A\quad and\quad C\longrightarrow A\quad are\quad { \lambda }_{ 1 },\quad { \lambda }_{ 2 }\quad and\quad { \lambda }_{ 3 }\) respectively, then which of the following relations is correct?
- (a)
\({ \lambda }_{ 1 }+{ \lambda }_{ 2 }+{ \lambda }_{ 3 }=0\)
- (b)
\({ \lambda }_{ 3 }^{ 2 }={ \lambda }_{ 1 }^{ 2 }+{ \lambda }_{ 2 }^{ 2 }\)
- (c)
\({ \lambda }_{ 3 }={ \lambda }_{ 1 }+{ \lambda }_{ 2 }\)
- (d)
\({ \lambda }_{ 3 }=\frac { { \lambda }_{ 1 }{ \lambda }_{ 2 } }{ { \lambda }_{ 1 }+{ \lambda }_{ 2 } } \)
The density of nucleus is of the order of
- (a)
103 kg m-3
- (b)
1012 kg m-3
- (c)
1017 kg m-3
- (d)
1024 kg m-3
When the number of nucleons in nuclei increase, the binding energy per nucleon
- (a)
increases continuously with mass number
- (b)
decreases continuously with mass number
- (c)
remains constant with mass number
- (d)
first increases and then decreases with increase of mass number
The rest energy of an electron is
- (a)
510 KeV
- (b)
931 MeV
- (c)
510 MeV
- (d)
931 kV
The mass number of a nucleus is
- (a)
always less than its atomic number
- (b)
always more than its atomic number
- (c)
sometimes equal to its atomic number
- (d)
sometimes more than and sometimes equal to its atomic number
The binding energy curve per nucleon as a function of atomic mass number shows a sharp peak for helium nucleus. This implies that helium
- (a)
can easily be broken up
- (b)
is very stable
- (c)
can be used as fissionable material
- (d)
is radioactive
Energy in the sun is generated mainly by
- (a)
fusion of radioactive material
- (b)
fusion of helium atoms
- (c)
chemical reaction
- (d)
fusion of hydrogen atoms
Binding energy of a nucleus is a measure of its
- (a)
stability
- (b)
mass
- (c)
charge
- (d)
momentum
The fusion of hydrogen into helium is more likely to take place
- (a)
at high temperature and high pressure
- (b)
at high temperature and low pressure
- (c)
at low temperature and low pressure
- (d)
at low temperature and high pressure
Fusion temperature is kept high because
- (a)
atoms are ionised at high temperature
- (b)
molecules break up at high temperature
- (c)
nuclei break up at high temperature
- (d)
kinetic energy is high enough to overcome repulsion between nuclei
The counting rate observed from the radio-active source at t = 0 second was 1600 counts per seond and t = 8 second it was 100 count per second. The counting rate per second at t = 6 second will be
- (a)
400
- (b)
300
- (c)
200
- (d)
150
A radioactive nucleus can decay by two different processes. The mean value of period for first process is t1 and that for the second process is t2. The effective mean period for two processes is
- (a)
\(1/2({ t }_{ 1 }+{ t }_{ 2 })\)
- (b)
\(({ t }_{ 1 }+{ t }_{ 2 })\)
- (c)
\(\sqrt { { t }_{ 1 }{ .t }_{ 2 } } \)
- (d)
\(\frac { { t }_{ 1 }{ t }_{ 2 } }{ { t }_{ 1 }+{ t }_{ 2 } } \)
The binding energy per nucleon of O16 is 7.97 MeV and that of O17 is 7.75 MeV. The energy in MeV required to remove a neutron from O17 is
- (a)
3.52
- (b)
3.64
- (c)
4.23
- (d)
7.86
The ionisation energy of 10 times ionised sodium atom is
- (a)
\(\frac { 13.6 }{ 11 } eV\)
- (b)
\(\frac { 13.6 }{ 112 } eV\)
- (c)
\(13.6\times { 11 }^{ 2 }eV\)
- (d)
\(13.6eV\)
According to Yukawa theory, the nuclear forces between the nucleons act through the exchange of
- (a)
position
- (b)
\(\mu -meson\)
- (c)
\(k-meson\)
- (d)
\(\pi -meson\)
The probability of a radioactive atom to survive 5 times longer than its half-life period is
- (a)
2/5
- (b)
2 X 5
- (c)
2-5
- (d)
25
In the process of fusion, the binding energy per nucleon
- (a)
decreases
- (b)
increases
- (c)
remains unchanged
- (d)
varies as energy is absorbed
The electron in a hydrogen atom makes a transition \(n\rightarrow n_2\), where n1 and n2 are the principal quantum numbers of the two states. The frequency of orbital motion of the electron in the initial state is 1/27 of that in the final state. The possible values of n1 and n2 are (assume the Bohr model to be valid.)
- (a)
n1=4, n2=2
- (b)
n1=3, n2=1
- (c)
n1=8, n2=1
- (d)
n1=6, n2=3
An electron in Bohr's theory of hydrogen atom has an energy of -3.4eV. The angular momentum of the electron is
- (a)
\(h\over \pi\)
- (b)
\(h\over 2\pi\)
- (c)
\(nh\over 2\pi\)
- (d)
\(2h\over \pi\)
A gas with hydrogen like atoms absorbs a radiation of 68eV. Consequently, the atoms emit radiations of only 3 wavelengths. The final state of atom is
- (a)
n=1
- (b)
n=3
- (c)
n=2
- (d)
n=4
A set of atoms in an excited state decays
- (a)
in general to any of the states with lower energy
- (b)
into a lower state only when excited by an external electric field
- (c)
all together simultaneously into a lower state
- (d)
to emit photons only when they collide
An electron in hydrogen atom after absorbing energy of photon jumps from energy state n1 and n2(n2>n1). Then it returns to ground state after emitting six different wavelengths in emission spectrum. The energy of emitted photons is either equal to, less than or greater than the absorbed photons. Then n1 and n2 are
- (a)
n1=4, n2=3
- (b)
n2=5, n1=3
- (c)
n2=4, n1=2
- (d)
n2=4, n1=1
Match the energy of electrons given in column I with their formula given in column II and select the correct option from the choices given below.
Column I | Column II |
---|---|
A. Potential energy of electron | 1.\(-{13.6\over n^2}eV\) |
B.Kinetic energy of electron | 2.\(-{kZe^2\over r_n}\) |
C. Total energy of hydrogen atom | 3.\(kZe^2\over 2r_n\) |
- (a)
A B C 1 3 2 - (b)
A B C 2 3 1 - (c)
A B C 3 2 1 - (d)
A B C 1 2 3
Which of the following transitions in hydrogen atoms emit photons of highest frequency?
- (a)
n=2 to n=6
- (b)
n=6 to n=2
- (c)
n=2 to n=1
- (d)
n=1 to n=2