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)
\({ \left( \frac { { Z }_{ Ag } }{ { Z }_{ Cu } } \right) }^{ 2 }\)
Rutherford's alpha-particle scattering experiment gave experimental information about
- (a)
the charge on alpha-particle
- (b)
the size of atom
- (c)
the size of nucleus
- (d)
the force between alpha-particle and proton in the nucleus
The ionisation energy of H2 is 13.6 eV. The ionisation energy of He atom would be
- (a)
13.6 eV
- (b)
27.2 eV
- (c)
6.8 eV
- (d)
54.4 eV
Frequency of the series limit of Balmer series of hydrogen atom in terms of Rydberg constant R and velocity of light c is
- (a)
\({ R }_{ c }\)
- (b)
\(\frac { { R }_{ c } }{ 4 } \)
- (c)
\(4{ R }_{ c }\)
- (d)
\(\frac { 4 }{ { R }_{ c } } \)
Which of the following transitions in a hydrogen atom emits photon of the highest frequency?
- (a)
n = 1 to n = 2
- (b)
n = 2 to n = 1
- (c)
n = 2 to n = 6
- (d)
n = 6 to n = 2
Rydberg constant is
- (a)
a universal constant
- (b)
same for all elements
- (c)
different for lighter elements but same for heavier elements
- (d)
different for different elements
A hydrogen atom in a state having a binding energy of 0.85 eV. makes a transition to a with an excitation energy of 10.2 eV. The energy of the emitted photon will be
- (a)
3.4 eV
- (b)
0.85 eV
- (c)
2.55 eV
- (d)
10.2 eV
In Bohr's model of the hydrogen atom the ratio between the period of revolution of an electron in the orbit of n = 1 to the period of revolution of the electron in the orbit n = 2 is
- (a)
1 : 2
- (b)
2 : 1
- (c)
1 : 4
- (d)
1 : 8
According to Bohr's theory of hydrogen atom, the angular momentum of an electron in any orbit of hydrogen atom is
- (a)
directly proportional to the radius of the orbit
- (b)
inversely proportional to the radius of the orbit
- (c)
directly proportional to the square of the radius of orbit
- (d)
directly proportional to the square root of the radius of the orbit
When a particle and an anti-particle combine the result is the emission of
- (a)
a heavier particle
- (b)
a photon
- (c)
a smaller particle
- (d)
two photons
The decay constant of \(_{ 80 }{ Po }^{ 206 }\) is \(\lambda \). Its half life and mean life respectively are
- (a)
\(\frac { 1 }{ \lambda } and\quad \frac { { log }_{ e }\quad 2 }{ \lambda } \)
- (b)
\(\frac { { log }_{ e }\quad 2 }{ \lambda } and\quad \frac { 1 }{ \lambda } \)
- (c)
\({ log }_{ e }\quad 2\quad and\quad \frac { 1 }{ \lambda } \)
- (d)
\(\frac { 1 }{ \lambda } \quad and\quad \lambda { log }_{ e }\quad 2\)
Complete the equation for the following fission process :
\({ _{ 92 }U }^{ 235 }+{ _{ 0 }n }^{ 1 }\longrightarrow ...+{ _{ 38 }Kr }^{ 90 }+...\)
- (a)
\({ _{ 54 }Xe }^{ 143 }+3{ _{ 0 }n }^{ 1 }\)
- (b)
\({ _{ 54 }Xe }^{ 145 }\)
- (c)
\({ _{ 57 }Xe }^{ 142 }\)
- (d)
\({ _{ 54 }Xe }^{ 142 }+{ _{ 0 }n }^{ 1 }\)
In the nuclear reaction \({ _{ 6 }C }^{ 11 }\longrightarrow _{ 5 }{ B }^{ 11 }+{ \beta }^{ + }+X,\) what does X stand for?
- (a)
An electron
- (b)
A photon
- (c)
Anti-neutrino
- (d)
A neutrino
The transition from the state n = 4 to n = 3 in a hydrogen-like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition
- (a)
\(2\longrightarrow 1\)
- (b)
\(3\longrightarrow 2\)
- (c)
\(4\longrightarrow 2\)
- (d)
\(5\longrightarrow 4\)
After n half times the fraction of amount which remains undecayed is
- (a)
\(\frac { 1 }{ { 2 }^{ n } } \)
- (b)
\(1-\frac { 1 }{ { 2 }^{ n } } \)
- (c)
\(1+\frac { 1 }{ { 2 }^{ n } } \)
- (d)
\({ 2 }^{ n }\)
From the following equations pick out the possible nuclear fusion reaction
- (a)
\({ _{ 6 }C }^{ 12 }+{ _{ 1 }H }^{ 1 }\longrightarrow _{ 7 }{ N }^{ 13 }+2\quad MeV\)
- (b)
\(4({ _{ 1 }H }^{ 1 })\longrightarrow _{ 2 }{ He }^{ 4 }+2{ e }^{ + }+26\quad MeV\)
- (c)
\({ _{ 1 }H }^{ 2 }+{ _{ 1 }H }^{ 2 }\longrightarrow { _{ 2 }He }^{ 4 }+Q\)
- (d)
ALL OF THE ABOVE
According to Yukawa theory, the nuclear forces between the nucleons act through the exchange of
- (a)
position
- (b)
\(\mu -meson\)
- (c)
\(k-meson\)
- (d)
\(\pi -meson\)
Boron has two isotopes 5B10 and 5B11. If the atomic weight of boron is 10.81, then the ratio of the two isotopes in the mixure is
- (a)
\(\frac { 19 }{ 81 } \)
- (b)
\(\frac { 10 }{ 11 } \)
- (c)
\(\frac { 20 }{ 53 } \)
- (d)
\(\frac { 29 }{ 73 } \)
Two radio-active substances X and Y initially have equal number of atoms. The substance X has half-life of one hour and Y has half-life of 2 hours. After 2 hours the ratio of the rate of disintegration of X to that of Y is
- (a)
1 : 2
- (b)
1 : 1
- (c)
2 : 1
- (d)
1 : 4
The average life of bound neutron in a nucleus is
- (a)
to absorb neutrons
- (b)
to cool the reactor
- (c)
to slow down the neutrons to thermal energies
- (d)
to control the energy released in the reactor
The essential distinction between X-rays and \(\gamma \)-rays is that
- (a)
\(\gamma \) - rays have smaller wavelength than X-rays
- (b)
\(\gamma \) - rays emanate from nucleus while X- rays emanate from other part of the atom
- (c)
\(\gamma \) - rays have greater ionising power than X-rays
- (d)
\(\gamma \) - rays more penetrating power than X-rays
The half-life of 215 At is 100 \(\mu s\). The time taken for the radio-activity of a sample of 215 At to decay to 1/16th of its initial value is
- (a)
400 \(\mu s\)
- (b)
6.3 \(\mu s\)
- (c)
40 \(\mu s\)
- (d)
300 \(\mu s\)
A hydrogen atom and a Li++ ion are both in the second excited state. If lH and lLi are their respective electronic momenta, and EH and ELi their respective energies, then
- (a)
\({ l }_{ H }>{ l }_{ Li }\quad and\quad \left| { E }_{ H } \right| >\left| { E }_{ Li } \right| \)
- (b)
\({ l }_{ H }={ l }_{ Li }\quad and\quad \left| { E }_{ H } \right| <\left| { E }_{ Li } \right| \)
- (c)
\({ l }_{ H }={ l }_{ Li }\quad and\quad \left| { E }_{ H } \right| >\left| { E }_{ Li } \right| \)
- (d)
\({ l }_{ H }<{ l }_{ Li }\quad and\quad \left| { E }_{ H } \right| >\left| { E }_{ Li } \right| \)
Electron in a hydrogen atom is replaced by an identically charged particle with mass 207 times that of electron. Now, the radius of K shell will be
- (a)
2.56X10-3Ao
- (b)
109.7X10-3Ao
- (c)
1.21X10-3Ao
- (d)
22174.4Ao
Difference between nth and (n+1)th Bohr's radius H-atom is equal to its (n-1)th Bohr's radius. The value of n is
- (a)
1
- (b)
2
- (c)
3
- (d)
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
The electron in a hydrogen atom makes transition from shell M to shell L. The ratio of magnitudes of initial to final centripetal acceleration of the electron is
- (a)
9:4
- (b)
81:16
- (c)
4:9
- (d)
16:81
The transition from the state n=4 to n=3 in a hydrogen like atom results in ultraviolet radiation. Infrared radiation will be obtained in the transition from
- (a)
\(2\rightarrow1\)
- (b)
\(3\rightarrow 2\)
- (c)
\(4\rightarrow 2\)
- (d)
\(5\rightarrow3\)