CBSE Questions for Class 12 Medical Physics Atoms Quiz 9 - MCQExams.com

What is alpha-particle?
  • The nucleus of hydrogen atom
  • The nucleus of deuterium
  • A fast moving proton
  • The nucleus of helium atom
If the first line of Lyman series has a wavelength $$1215.4\mathring { A } $$, the first line of Balmer series is approximately
  • $$4864\mathring { A } $$
  • $$1025.5\mathring { A } $$
  • $$6563\mathring { A } $$
  • $$6400\mathring { A } $$
The wavelength of spectral line coming from a distant star shifts from $$600nm$$ to $$600.1 nm$$. The velocity of the star relative to earth is 
  • $$50 km s^{-1}$$
  • $$100 km s^{-1}$$
  • $$25 km s^{-1}$$
  • $$200 km s^{-1}$$
In the Davisson and Germer experiment, the velocity of electrons emitted from the electron gun can be increased by
  • increasing the potential difference between the anode and filament
  • increasing the filament current
  • decreasing the filament current
  • decreasing the potential difference between the anode and filament
Cathode rays were discovered by
  • Maxwell Clerk James
  • Heinrich Hertz
  • William Crookes
  • J. J. Thomson
Photons have properties similar to that of.
  • Both particles and waves
  • Particles
  • Waves
  • Neither particles nor waves
Number of spectral line in hydrogen atom is
  • $$6$$
  • $$8$$
  • $$15$$
  • None of the above
The photon energy in units of eV for electromagnetic waves of wavelength $$2 cm$$ is:
  • $$2.5 10^{-19}$$
  • $$5.2 10^{-16}$$
  • $$3.2 10^{-16}$$
  • $$6.2 10^{-5}$$
The ionization energy of a hydrogen like Bohr atom is $$4$$ Rydbergs. (i) What is the wavelength of the radiation emitted when an electron jumps from the first excited state to the ground state? (ii) What is the radius of the first orbit for this atom?
  • $$300\overset {\circ}{A}, 2.65\times 10^{-11}m$$.
  • $$600\overset {\circ}{A}, 2.65\times 10^{-11}m$$.
  • $$300\overset {\circ}{A}, 4\times 10^{-11}m$$.
  • $$600\overset {\circ}{A}, 4\times 10^{-11}m$$.
A double ionized lithium atom is hydrogen-like with atomic number $$3$$.
(a) Find the wavelength of the radiation required to excite the electron in $$Li++$$ from the first to the third Bohr orbit. (Ionization energy of the hydrogen atom equals $$13.6\ eV$$)\
(b) How many spectral lines are observed in the emission spectrum of the above excited system?
  • $$114.7\ A^{\circ}$$, Three lines.
  • $$113.7\ A^{\circ}$$, four lines.
  • $$115.7\ A^{\circ}$$, two lines.
  • $$116.7\ A^{\circ}$$, one lines.
An electron with energy $$12.09$$ eV strikes hydrogen atom in ground state and gives its all energy to the hydrogen atom. Therefore hydrogen atom is excited to __________ state.
  • Fourth
  • Third
  • Second
  • First
The radius of second orbit in an atom of hydrogen is R. What is the radius in third orbit.
  • $$3R$$
  • $$2.25R$$
  • $$9R$$
  • $$\dfrac{R}{3}$$
In the Bohr model of the hydrogen atom.
  • The radius of the $$n^{th}$$ orbit is proportional to $$n^{2}$$
  • The total energy of the electron in the $$n^{th}$$ orbit is inversely proportional to $$'n'$$
  • The angular momentum of the electron in an orbit is an integral multiple of $$h/2\pi$$
  • The magnitude of the potential energy of the electron in any orbit is greater than its kinetic energy
If element with principal quantum number $$n > 4$$ were not allowed in nature, the number of possible elements would be
  • $$60$$
  • $$32$$
  • $$4$$
  • $$64$$
A single electron orbits around a stationary nucleus of charge $$+Ze$$, where $$Z$$ is a constant and $$e$$ is the magnitude of the electronic charge. It required $$47.2\ eV$$ to excite the electron from the second Bohr orbit to the third Bohr orbit.
Find The wavelength of the electromagnetic radiation required to remove the electron from the first Bohr orbit.
  • $$36.4$$
  • $$53$$
  • $$40$$
  • $$66$$
The number of waves in the third orbit of H atom is
  • 1
  • 2
  • 4
  • 3
The total energy of in the electron in the hydrogen atom in the ground state is $$-13.6\ eV$$. Which of the following is its kinetic energy in the first exited state?
  • $$13.6 \ eV$$
  • $$6.8 \ eV$$
  • $$3.4 \ eV$$
  • $$1.825 \ eV$$
The radius of the first Bohr orbit is $$a_{0}$$. The $$n^{th}$$ orbit has a radius:
  • $$na_{0}$$
  • $$a_{0}/n$$
  • $$n^{2}a_{0}$$
  • $$a_{0}/n^{2}$$
The average current due to an electron orbiting the proton in the $$n^{th}$$ Bohr orbit of the hydrogen atom is
  • $$\propto n$$
  • $$\propto n^{3}$$
  • $$\propto n^{-3}$$
  • none of these
The ionisation potential of a hydrogen atom is $$13.6\ volt$$. The energy required to remove an electron from the second orbit of hydrogen is:
  • $$3.4\ eV$$
  • $$6.8\ eV$$
  • $$13.6\ eV$$
  • $$27.2\ eV$$
The radius of the shortest orbit in a one-electron system is $$18\ pm$$. It may be
  • Hydrogen
  • Deuterium
  • $$He^{+}$$
  • $$Li^{2+}$$
Three photons coming from emission spectra of hydrogen sample are picked up. Their energies are $$1eV, 10.2eV$$ and $$1.9eV$$ . These photons must come from
  • a single atom
  • two atoms
  • three atom
  • either two atoms or three atoms
The ratio of the speed of an electron in the first orbit of hydrogen atom to that in the first orbit of $$He^{+}$$ is
  • $$1\ :\ 2$$
  • $$2\ :\ 1$$
  • $$1\ :\ 4$$
  • $$4\ :\ 1$$
The electron in a hydrogen atom makes a transition $$n_1\rightarrow n_2$$ whose $$n_1$$ and $$n_2$$ are the principal quantum numbers of the two states. Assume the Bohr model to be valid. The frequency of orbital motion of the electron in the initial state is $${1/27}$$ of that in the final state. The possible value of $$n_1$$ and $$n_2$$ are
  • $$n_1=4,n_2=2$$
  • $$n_1=3, n_2=1$$
  • $$n_1=8,n_2=1$$
  • $$n_1=6, n_2=3$$

The key feature Of Bohr's theory Of spectrum Of hydrogen atom is the quantization Of angular momentum when an electron is revolving around a proton. We will extend this to a general rotational motion to find quantized rotational energy Of a diatomic molecule assuming it to be rigid. The rule to be applied is Bohr's quantization condition.A diatomic molecule has moment Of inertia I. By Bohr's quantization condition its rotational energy in the nth level (n=0 is not allowed) is 
  • $$\cfrac{h^2}{(n^2)(8\pi^2I)}$$
  • $$\cfrac{h^2}{(n)(8\pi^2I)}$$
  • $$\cfrac{n h^2}{8\pi^2I}$$
  • $$\cfrac{n^2 h^2}{(8\pi^2I)}$$
An electron in hydrogen atom makes a transition $$n_{1}\rightarrow n_{2}$$ where $$n_{1}$$ and $$n_{2}$$ are principal quantum numbers of the two states. Assuming Bohr's model to be valid, the time period of the electron in the initial state is eight times that in the final state. The possible values of $$n_{1}$$ and $$n_{2}$$ are
  • $$n_{1} = 6$$ and $$n_{2} = 2$$
  • $$n_{1} = 8$$ and $$n_{2} = 1$$
  • $$n_{1} = 8$$ and $$n_{2} = 2$$
  • $$n_{1} = 4$$ and $$n_{2} = 2$$
If photons of energy $$12.75eV$$ are passing through hydrogen gas in ground state then no of lines in emission spectrum will be 
  • $$6$$
  • $$4$$
  • $$3$$
  • $$2$$
In a hypothetical Bohr hydrogen, the mass of the electron is doubled. The energy $$E_o$$ and the radius $$r_o$$ of the first orbit will be ($$a_o$$ is the bohr radius)
  • $$E_o=-27.2eV;r_o=a_o/2$$
  • $$E_o=-27.2eV;r_o=a_o$$
  • $$E_o=-13.6eV;r_o=a_o/2$$
  • $$E_o=-13.6eV;r_o=a_o$$
The absorption transition between the first and the fourth energy states of hydrogen atom are $$3$$. The emission transition between these states will be:
  • $$3$$
  • $$4$$
  • $$5$$
  • $$6$$
Two samples of radium, each of mass $$1\ mg$$ and $$0.1\ mg$$, are taken to study the emission of alpha particles. It will be observed that
  • Both samples will emit the same number of alpha particles
  • $$1\ mg$$ of radium will emit $$10$$ times the number of alpha particles per second than $$0.1\ mg$$ does
  • Emission of alpha particles is independent of mass of the samples
  • $$0.1\ mg$$ of radium will emit ten times more than that by $$1\ mg of radium
If the difference between $$(n + 1)^{th}$$ Bohr radius and $$n^{th}$$ Bohr radius is equal to the $$(n -1)^{th}$$ Bohr radius then find the value of $$n$$
  • $$4$$
  • $$3$$
  • $$2$$
  • $$1$$
Consider an atom of $${Li}^{2+}$$ which is a uni-electron system and hence Bohr's model is applicable to it.
If $${r}_{0}=$$ radius of first orbit in hydrogen atom, what is the radius of revolution of electron in second excited state in $${Li}^{2+}$$?
  • $${r}_{0}$$
  • $$2{r}_{0}$$
  • $$3{r}_{0}$$
  • $$9{r}_{0}$$
In an atom an electron excites to the fourth orbit. When it jumps back to the energy levels a spectrum is formed.Total number of spectral lines in this spectrum would be 
  • 3
  • 4
  • 5
  • 6
The radius of the first orbit of the electron of a hydrogen atom is $$5.3\times 10^{-11}$$m. What is the radius of its second orbit?
  • $$21.1\times 10^{-11}$$m.
  • $$31.1\times 10^{-11}$$m.
  • $$51.1\times 10^{-11}$$m.
  • $$81.1\times 10^{-11}$$m.
The wavelengths involved in the spectrum of deuterium $$\left( ^{2}_1D\right)$$ are slightly different from the hydrogen spectrum, because:
  • Sizes of the two nuclei are different
  • Nuclear forces are different in the two cases
  • Masses of the two nuclei are different
  • Attraction between the electron and the nucleus in different in the two cases
A Proton and an $$/alpha $$ particle are accelerated through a potential difference of 100V. The ratio of the wavelength associated with the proton to that associated with an $$/alpha $$ particle is
  • $$1:2$$
  • $$2:1$$
  • $$22:1$$
  • $$2 \sqrt{2} : 1$$
Electrons accelerated from rest by a potential difference of $$12.75V$$, are bombarded on a mono-atomic hydrogen gas. Possible emission of spectral lines are:-
  • First three Lyman lines, first two Balmer's lines and first Paschen line
  • First three Lyman lines only
  • First two Balmer's lines only
  • None of the above.
A positroniuim  consists of an electron and a positron revolving about their common centre of mass. Calculate the kinetic energy of the electron in ground state:
  • $$1.51\ eV$$
  • $$3.4\ eV$$
  • $$6.8\ eV$$
  • $$13.6\ eV$$
Energy required for the electron excitation in $$Li^{++}$$ from the first to the third Bohrs orbit:
  • $$7.625\times { 10 }^{ 28 }mev$$
  • $$109 ev$$
  • $$8.8\times { 10 }^{ -28 }mev$$
  • $$56ev$$
The ground state energy of $$H$$- atom is $$-13.6eV$$. The energy needed to ionise $$H$$- atoms from its second excited state is:
  • $$1.51eV$$
  • $$3.4eV$$
  • $$13.6eV$$
  • $$12.1eV$$
In a sample of hydrogen like atoms all of which are in ground state , a photon beam containing photons of various energies is passed.In absorption spectrum, five dark lies are observed. The number of bright lines in the emission spectrum will be (Assume that all transitions take place)
  • 5
  • 10
  • 15
  • none of these
A proton, a direction ion and an $$\alpha$$-particle of equal kinetic energy perform circular motion normal to a uniform magnetic field $$B$$. If the radii of their paths are $$r_p, r_d$$ and $$r_\alpha$$ respectively then [Here, $$q_d = q_p, m_d = 2m_p$$]
  • $$r_\alpha = r_p > r_d$$
  • $$r_\alpha = r_p< r_d$$
  • $$r_\alpha > r_d > r_p$$
  • $$r_\alpha = r_d = r_p$$
If radiation of all wavelengths from ultraviolet to infrared is passed through hydrogen gas at room  temperature absorption lines will be observed in the 
  • Lyman series
  • Balmer's series
  • Both (1) and (2)
  • Neither (1) or (2)
The radius of first orbit of hydrogen atom is $$0.53\ A$$. The radius of its fourth orbit will be-
  • $$0.193\ A$$
  • $$4.24\ A$$
  • $$2.12\ A$$
  • $$8.48\ A$$
If in Bohr's atomic model, it is assumed that force between electron the proton varies inversely as $${r^4},$$b energy of the system will be proportional to:
  • $${n^2}$$
  • $${n^4}$$
  • $${n^6}$$
  • $${n^8}$$
In a hydrogen atom, the electron revolves round the proton in a circular orbit of radus $$0.528 \mathring {A}$$ with a speed of $$2.18 \times 10^6$$ m/s. Calculate the centripetal force acting on the electron. (Mass of electron = $$9.1 \times 10^{-31}kg. I \mathring {A}=10^{-10}m)$$
  • $$10.2 \times 10^{-8}$$
  • $$8.2 \times 10^{-8}$$
  • $$9.2 \times 10^{-8}$$
  • $$7.2 \times 10^{-8}$$
The wave number of the radiation whose quantum is $$1erg$$ is
  • $$5\times {10}^{15}{Cm}^{-1}$$
  • $$15\times {10}^{5}{cm}^{-1}$$
  • $$1.5\times {10}^{-15}{cm}^{-1}$$
  • $$5\times {10}^{-21}{cm}^{-1}$$
The radius of the first orbit of the $$e^-$$ of a hydrogen atom is $$5.3\times 10^{11}m$$, what is the radius of its second orbit.?
  • $$3.12\times 10^{-10}m$$
  • $$2.12\times 10^{-10}m$$
  • $$4.12\times 10^{-10}m$$
  • $$5.12\times 10^{-10}m$$
The lifetime of an electron in the state $$n=2$$ in the hydrogen atom is about 
  • $$10\ ns$$
  • $$1000\ ns$$
  • $$1\ ms$$
  • $$10\ ms$$
The moment of momentum of electrons in the third orbit in a hydrogen atom 
  • $$31.67 \times 10^{-34} gm \ m^2/s$$
  • $$3.167 \times 10^{-34} kg \ m^2/s$$
  • $$31.67 \times 10^{-34} kg \ cm^2/s$$
  • $$31.67 \times 10^{-34} gm \ cm^2/s$$
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