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CHAPTER # 20 (ATOMIC SPECTRA)

TEXT BOOK QUESTIONS
i. Bhor’s theory of hydrogen atom is based upon several assumptions. Do any of these
assumption s contradict classical physics?
Ans: First postulate of Bohr’s atomic model contradicts with classical physics. According to
this postulate, electrons radiate no energy while revolving around the nucleus.
But according to classical physics, electrons radiate energy continuously while
revolving around nucleus. Due to emission of radiation, the electrons gradually come close to
the nucleus and ultimately fell into it.
Hence, Bohr’s theory contradicts classical physics.

ii. What is meant by a line spectrum? Explain, how line spectrum can be used for the
identification of elements?
Ans. When electron jumps form a higher orbit to lower orbit it emits photons of energy.

hf
=
This emission of photons constitute line spectrum of atom. Different elements emit line
spectrum of different set of wavelengths. This means spectrum of each element different form
other. Therefore, by spectrum study, we can identify elements.

iii. Can the electron in the ground state of hydrogen atom absorb a photon of energy
13.6 eV or greater than 13.6 eV?
Ans. Yes, electron can absorb photon of energy 13.6 eV or grater than 13.6 eV.
Reason: Since the ionization energy of electron in ground state is 13.6 eV (in hydrogen
atom). Therefore, minimum energy required is 13.6 eV. If the energy is greater than 13.6 eV
then surplus energy will be given to electron as K.E.

iv. How can the spectrum of hydrogen contain so many lines when hydrogen contains
one electron?

Ans. No doubt hydrogen has only one electron which is present in ground state but there
are
many other higher energy states present above ground level. So when a hydrogen atom is excited
from some external source then its electron jumps to some higher energy level. When this
electron falls back then it can go to ground state in different steps. At each downward jump it
will emit a light photon of particular wavelength.
Lyman, Balmer, Paschen etc., are due to result of these emissions.
______________________________________
v. Is energy conserved when an atoms emits a photon of light?
Ans. Yes energy is conserved when an excited atom emits a photon of light. Because energy
emitted during its de excitation is exactly balanced by the energy absorbed during its excitation.
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vi. Explain why a glowing gas gives only certain wavelength of light and why that gas is
capable of absorbing the same wavelengths? Give a reason why it is transparent to
other wavelengths?
Ans. Each and every element emits and absorbs radiations of some specific wavelength. Hence
when certain radiations are incident on this element then it will absorb only those radiations
which it can also emit. Therefore, it is transparent to other wavelengths.
_____________________________________
vii. What do we mean when say that the atom is excited?
Ans. When an atom in its normal state is provided energy form some external source then its
electrons jump form a lower energy level to a high energy level then the atom is said to be in
an excited state.
______________________________________
viii. Can X – rays be reflected, refracted, diffracted and polarized just like any other
waves? Explain.
Ans. X – rays are electromagnetic waves and they can be reflected, refracted, and polarized but
their conditions may be different from that of ordinary light e.g., light can be diffracted by
diffraction grating but X- rays cannot be diffracted by grating but X – rays are diffracted by
crystals.
______________________________________
ix. What are the advantages of lasers over ordinary light?
Ans. The laser light is intense and coherent so it does not spread while passing through a
medium, its energy can be focused at a point to get enough energy for welding, cutting and as
surgical tool which ordinary light cannot do.
______________________________________
x. Explain why laser action could not occur without population inversion between
atomic levels?
Ans. If there is no population inversion between atomic levels then laser light will not be
obtained. A large number of excited atoms gather at population inversion which emit a large
number of coherent photons along the same direction of motion. It is impossible without
population inversion.

IMPORTANT SHORT QUESTIONS

xi. What is spectroscopy?
Ans. Spectroscopy:
The branch of physics that deals with the investigation of wavelengths and intensities of
electromagnetic radiations emitted or absorbed by atom is called spectroscopy.
There are three types of spectra:
(1) continuous spectra
(2) Band spectra, and
(3) Discrete or line spectra
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xii. What is meant by atomic spectrum? Can we call it line spectrum?

Ans. Atomic Spectra:
When an atomic gas or vapour at much less than atmospheric pressure is excited (usually by
passing an electric current through it) then it de excites and emitted radiations form a spectrum
which contains certain specific wavelength only.
An idealized arrangement for observing such atomic spectra is shown in figure.
If is for the reason that spectrum is referred to as line spectrum.
______________________________________
xiii. What do you mean by spectral lines? Write down the spectral series.
Ans. Spectral Lines:
In 19th century it was also found that spectrum of any element. Contains wavelengths in a definite
regularity. There regularities were classified into certain groups called the spectral series.
Series:
(i) Lyman series (ii) Balmer series (iii) Paschen series
(iv) Bracket series (v) Pfund series
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xiv. What is Balmer series? What series of wavelength it contains?
Ans. Balmer series:
The first such series was identified by J.J Balmer in 1885 in the spectrum of hydrogen atom. This
series, called the Balmer series, is shown in figure.
The results obtained by Balmer were expressed in 1896 by J.R Rydberg in the following
mathematical form

Where Is the Rydberg constant. Its value is .

The Balmer series contain wavelengths in the visible portion of the hydrogen spectrum. There are
some other series which fall in ultraviolet and infrared regions.
______________________________________
xv. What series of spectral lines lies in ultraviolet region? Also fire the formal of series.
Ans. Lyman Series:
Lyman series fall in the series of ultraviolet region. Its empirical formula is given by:

=
Where;
n = 2,3,4, ……
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xvi. What series of spectral lines lie in infrared region? Give empirical formula of each.
Ans. In infrared region, there spectral series have been found whose lines have wavelengths
given by formulae.
Paschen Series:

=
Where;
n = 4,5,6, …...
Bracket Series:

=
Where;
n = 5,6,7, …...
Pfund Series:

=
______________________________________
xvii. State Elastic Pastulates of Bohr’s atomic model.
Ans. Pastulate I:
An electron bound to the nucleus in an atom, can move around the nucleus in certain circular
orbits without radiating. These orbits are called the discrete stationary states of the atom.
Pastulate II:
Only those stationary orbits are allowed for which orbital angular momentum is equal to an

integral multiple of i.e.,

mvr = …… (1)
where;
n = 1,2,3, ….., and n is called the principal quantum number.
m and v are mass and velocity of orbiting electron respectively, and h is plank’s constant.
Pastulate III:
Wherever an electron makes a transition, that is, jumps from high energy state …….. to a

lower energy state , a photon of energy hf is emitted so that

hf = …….. (2)
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xviii. How did de – Broglie interpret Bohr’s 2nd Pastulate?
Ans. We know, if I is length of an orbit, then:

I =
Where;

I = Length of orbit =

= ……… (1)
From de – Broglie’s hypothesis:

= ………. (2)
Comparing (1) and (2)

= nh

mvr =
which is Pastulate II.
______________________________________
xix. What do you mean by ionization energy?
Ans. Ionization Energy:

= = Constant = - 13.6 eV
Which is energy required to remove an electron completely from the first Bohar orbit. This is
called ionization energy.
“The amount of energy required to remove completely an electron from Bohr orbit is
called ionization energy”.
The ionization energy may be provided by collision with an external electron.
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xx. Differentiate ionization potential and excitation potential.
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Ans. Ionization potential:

The minimum potential through which the external electron should be accelerated so that it can
supply the requisite ionization energy is known as ionization potential.
Excitation Potential:
The potential through which an electron should be accelerated so that on collision it can lift the
electron in the atom from ground state to some higher state is known as excitation potential.
______________________________________
xxi. What do you understand by ground state and excited state?
Ans. Ground State:
When the electron is in the first Bohr orbit, it is said to be in ground state.
Excited State:
When the electron is in the higher orbits, it is said to be in excited state.
The atom may be excited by collision with externally accelerated electron.
______________________________________
xxii. What do you mean by characteristic X – rays?
Ans. Characteristics X – rays:
The inner shell electrons are tightly bound and large amount of energy is required for their
displacement form their normal energy level. After excitation, when an atom returns to its
normal state, photons of larger energy are emitted, thus transition of inner shell electrons in
heavy atoms give rise to the emission of high energy photons or X – rays. These X – rays
consists of series of specific wavelength or frequencies and hence are called characteristic X –
rays.
______________________________________

xxiii. How do you get X – rays X – rays ?

Ans. Characteristics X – rays:

X – rays; The electron form the L shell humps to occupy the hole in the K shell, emitting a

photon of energy called the X – rays given by

X – rays; it is also possible that the electron from the M shell might also jump to occupy the

hole in the K – shell, emitting a photon of energy called the X – rays given by

=
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xxiv. What do you understand by term “Bremsstrahlung”? explain
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Ans. Bremsstrahlung or Continuous X – rays Spectrum:

The continuous spectrum is due to an effect known as bremsstrahlung or breaking radiation when
the fast moving electrons
bombard the target, they are suddenly slowed down on impact with the target. We know that an
accelerating charge emits electromagnetic radiation. Hence, these impacting electrons emit
radiation as they are strongly decelerated by the target. Since the rate of deceleration is so
large, the emitted radiation corresponding to short wavelength and so the bremsstrahlung is in
the X – rays region.
______________________________________
xxv. Does electron reside inside or outside the nucleus? Justify your answer.
Ans. Does Electron Reside Inside the Atom:
Now we see can an electron reside inside the atom? To find this, we calculate the speed of an
electron. If it is found less than speed of light then there are expectations of finding the electron
within the atom but outside the nucleus.

The radius of the hydrogen atom is about m.

Again applying Heisenberg’s principle:

=
As;

=
Putting values, we get;

=
Result:
This speed of the electron is less than the speed of light, therefore, it can exist in the atom but
outside the nucleus.
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xxvi. There is uncertainty that whether electron reside inside the nucleus or inside the
atom but outside nucleus. Justify.
Ans. Does Electron Reside Inside Nucleus:
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As the typical nuclei are less than m in diameter. Therefore, for an electron to be confined
within such nucleus, the uncertainty in its position must be of the order of size of atom i.e.,

m.
The corresponding uncertainty in electron momentum is

=
As;

= =
Conclusion:
Hence for the electron to be confined to a nucleus its speed would have to be greater than

i.e., greater than the speed of light which is impossible. Therefore, we can conclude
that an electron can never be found inside a nucleus.
______________________________________
xxvii. What do you understand by spontaneous emission?
Ans. When the atom is in excited state, two things can happen to the atom.
Spontaneous Emission:
The atom can decay by spontaneous emission as shown in Gig. (b) in which the atom emits a

photon of energy hf = in any arbitrary direction .

Induced Emission:

The other alternative for the atom in the excited state is to decay by stimulated or induced

emission as shown in Fig.(c). In this case the incident photon of energy hf = Induces the
atom to decay by emitting a photon that travels in the direction of the incident photon.
______________________________________
xxviii. “Laser” is acronym stands for? Why we use Laser’s?
Ans. Laser:
Laser is the acronym for light amplification by stimulated emission of radiation. Lasers are used
for producing an intense, monochromatic and unidirectional coherent beam of light.
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xxix. Population inversion is basic need of laser to function. How does you achieve this?
Ans. Population Inversion and Laser Action:
Let us consider a simple case of a material whose atoms can reside in three different states as
shown in figure.

State which is ground state; , the excited state in which the atom can reside only for

sec. and the metastabel state in which the atoms can reside for s, much longer than

s. a metastabel state is an excited state in which an excited electron is unusually stable

and from which the electron spontaneously falls to lower state only after relatively longer time.

Thus the only alternative for the atoms in the excited state is to decay spontaneously to

state , the atoms reach state much faster than they leave state this eventually leads

to the situation that the state contains more atoms than state this situation is known as
population inversion.
xxx. Give any there uses of laser in medicine.
Ans. Uses of Laser in Medicine:
(1) Laser beams are used s surgical tool for “welding” detached retinas.
(2) The narrow intense beam of laser can be used to destroy tissue in a
localized area. Tiny organelles with a living cell have been destroyed by using laser to study
how the absence of that organelle affects the behaviour of the cell.
(3) Finely focused beam of laser has been used to destroy cancerous and pre
– cancerous cell.
(4) The heat of the laser seals off capillaries and lymph vessels to prevent
spread of disease.
xxxi. Give any three uses of laser in general.
Ans. Uses of Laser:
(1) The intense heat produced in small areas by a laser beam is used for
welding and machining metals and for drilling tiny holes in hard materials.
(2) The precise straightness of a laser beam is also useful to surveyors for
lining up equipment especially in inaccessible locations.
(3) It is potential energy source for inducing fusion reactions.
(4) It can be used for telecommunication along optical fibers.
(5) Laser beam can be used to generate three dimensional images of objects
in a process called holography.
xxxii. Why we get red light in Helium – neon laser?
Ans. Spontaneous emission from neon atoms initiate laser action and stimulated emission causes
electrons in the neon to drop from 20.66 eV to the 18.70 eV level. The difference of energy
20. 66 eV – 18.70 eV = 1.96 eV is generated which is the energy of red light of wavelength
632.8 nm.

MULTIPLE CHOICE QUESTION

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TOPIC: ATOMIC SPECTRA

No QUESTION A B C D
.
1. Spectroscopy is a branch of physics Emission Wavelength Absorption All of these
which deals with the study of ____ of
electromagnetic radiation
2. The branch of physics which deals Spectrography Spectroscopy Nuclear physics Plasma physics
with the productions, measurement
and interaction of electromagnetic
spectra arising from either emission
or absorption of radiant energy by
various substances is called
3. A radiation spectrum which in Contiguous Band spectra Discrete None of these
continuously distributed over a spectra spectra
frequency region without being
broken up into lines or bands is
known as
4. A spectrum consisting of groups or Continuous Band spectra Discrete None
bands of closely spaced lines in spectra spectra
emission or absorption characteristics
of molecular gases and chemical
compounds is known as
5. A spectrum of radiation is which the Continuous Band spectra Discrete None
quantity being studied, such as spectra spectra
frequency or energy, takes on
discrete values is called
6. Which of the following is an example Black body Molecular Atomic spectra None
of band spectra? radiation spectra
spectrum

7. Which of the following is an example Black body Molecular Atomic spectra None
of band spectra? radiation spectra
spectrum

8. Which of the following is an example Black body Molecular Atomic spectra None
of line spectra? radiation spectra
spectrum

9. The spectrum of radiation due to Black body Molecular Atomic spectra None
transitions between energy levels in radiation spectra
an atom, either absorption or spectrum
emission is called
10. Who identified the first series is the Lyman Pfund Balmer Bracket
spectrum of hydrogen?
11. Balmer identified the spectral lines in 1785 1885 1936 None
the spectrum of hydrogen in
12. Balmer series lies in the Visible region Ultraviolet Infrared region All of these
region

13. The value of Rydberg’s constant is

equal to
14. J.R. Rydberg’s obtained a formula to 1886 1894 1896 1903
describe the wavelength of the
hydrogen atom in
15. The wavelengths of Lyman series for Visible region Ultraviolet Infrared region None of these
hydrogen spectrum lies in the region

16. The wavelengths Paschan series for Visible region Ultraviolet Infrared region None of these
the hydrogen spectrum lies in the region
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17. Brackett and Pfund series of spectral Visible region Ultraviolet Infrared region Far-infrared
lines lies in the region region

18. When an electron in an atom of

hydrogen jumps from an outer orbit
n=3 to an inner orbit n=2, the
wavelength of emitted radiations will
be equal to?
19. In the spectrum of which of the Oxygen Nitrogen Hydrogen All of these
following will you find Balmer series?
20. Which of the following can exist only Principal Linear Angular Azimuthal
quantum momentum momentum quantum
number number
in integral multiples of , according
to assumption of Bohr’s theory?
21. If hydrogen gas I bombarded at room Lyman series Shortest Longest All series will
temperature with electrons wavelength of wavelength of appear
possessing different energies, the Lyman series Lyman sires together
wavelength of radiations first emitted
from the gas will correspond to
22. Lines of Balmer series are emitted by From the first From higher From higher From the third
hydrogen atom when the electron orbit to any orbits to orbits to orbit to higher
jumps other orbit second orbit second orbit orbit

23. The frequency of the first line in the

Lyman series for hydrogen is found
to be approximately

24. Hydrogen emits blue light when it Red Yellow Green Violet
changes form n=4 energy level to
n=2 energy level. Which colur of light
will be emitted when the electron in
this atom jumps from n=5 to n=2?
25. Which of the following series lies in Lyman series Paschen series Balmer series Pfund series
the visible region of the
electromagnetic spectrum?
26. Which of the following is one of the Balmer series Bracket series Pfund series All of these
spectral series of atomic hydrogen?
27. The Balmer series is found in the Hudrogen Nitrogen Oxygen All
spectrum of
28. Number of the mission spectra are One Three Two Four

29. Dimension of Rydberg’s constant is

30. Number of series lies in infra red One Three Two Four
region for hydrogen atom is / are
31. To find longest wavelength radiation 2 4 3
in Balmer series, the value of n used
is
32. The following gas was identified in Hydrogen Helium Carbon Nitrogen
the sun using spectroscopy
33. Hydrogen atom spectrum does not lie Ultraviolet Visible region Infra-red X-ray region
in region region

34. Balmer series in

mathematical form
can be expressed as
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35. Lyman series

contains the
wavelength gives by
the formula
36. Mathematically,
Paschan series can
be expressed as

37. Bracket series can be

expressed as

38. Mathematically,
Pfund series is
written as

TOPIC: BOHR’S MODEL OF HYDROGEN ATOM

No QUESTION A B C D
.

1. Neill Bohr made his 1897 1905 1913 1921

three postulates in

2. According to 1st Continuously Without Both ‘a’ &’b’ None

postulate of Bohr’s radiating energy radiating energy
theory, an electron can
move around the
nucleus in circular
orbits

3. According to Bohr’s 2nd

postulate

4. According to 3rd
postulate of Bohr’s
theory

5. An expression for
electrostatic force
between the electron
and the nucleus of
hydrogen atom is given
by

6. As the electron is
revolving around the
nucleus the centripetal
force acting on it is
given by

7. The radius of nth orbit

of hydrogen atom can
be determined by the
formula

8. The value of Planck’s

constant is
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9. The radius of 1st Bohr’s 0.53m 0.53nm 0.053nm 0.53mm

orbit for hydrogen atom
is

10. The P.E. of an electron

reviling at a distance ‘rn’
from the nucleus is

11. The total energy of an

electron in nth orbit of
the hydrogen atom is
given by

12. An expression for

ground state energy of
an electron is given by

13. The ionization energy -11.6eV -12.6eV -13.6eV -19.6eV

for hydrogen atom is

14. What is the relation

between Rydberg
constant and ground
state energy (En)?

15. When an electron exists Normal state Ground state Excited state Both ‘a’ & ‘b’
is this lowest state, it is
called

16. The potential due to Potential Excitation Ionization All of these

which an electron is gradient potential potential
lifted from ground state
to excited state is called

17. For a hydrogen atom,

the speed of an
electron in the nth orbit
is given by

18. The first Bohr atom in

the hydrogen atom has
a radius

19. The SI unit of m m-1 m-2 Nm-1

Rydberg’s constant is

20. According to Bohr’s Perfect circle of A circle of An ellipse A circle of an

atomic model, an any radius continuously allowed radius
electron can revolve decreasing
around a proton radius
indefinitely, if its path is

21. As the quantum Increases Decreases Remains the Both ‘a’ and ‘b’
number increases, the same
difference of energy
between two
consecutive energy
 P a g e | 14

levels

22. According to Bohr’s Kinetic energy Potential energy Linear Angular

theory, which of the momentum momentum
following takes discrete
values?

23. In an atom of hydrogen 8.45 Ao 4.85 Ao 5.84 Ao 0.845 Ao

if the radius of first
orbit is 0.528Ao then
the radius of 4th orbit is
approximately.

24. An atom makes a

transition from a state
of energy E2 to one of
lower energy E1. Which
of the following gives
the wavelength of the
radiation emitted, in
terms of the Planck’s
constant ‘h’ and the
speed of light ‘c’?

25. Who introduced the Raman Bohr Newton Fermi

concept that an atom
possess quantized
energy levels?

26. In which of the When it is When it jumps When it goes None of the
following an electron moving in any from higher from lower above
emits energy? specified orbit energy level to energy level to
lower energy higher energy
level level

27. The angular speed of Directly Directly Inversely Inversely

an electron in the nth proportional to n proportional to proportional to proportional to n
orbit of Bohr’s n2 n2
hydrogen atom is

28. According to Bohr’s Directly Inversely Directly Directly

theory of hydrogen proportional to r proportional to r proportional to proportional to
atom the velocity of square root of r square of r
electron in the orbit of
radius r is

29. According to Bohr’s

theory the radius of
quantized orbit is given
by

30. Ionization of a 12.3eV 13.5eV 4.2J 2.4J

hydrogen atom
originally in its ground
state takes a minimum
amount of energy equal
to
 P a g e | 15

31. The first successful David Bohm Louis de Broglie Neil Bohr J.J. Thomson
quantitative theory of
atomic structure was
formulated by

32. The energy in electron Faraday energy Wave number Ionization Excitation
volts necessary to potential potential
remove the most
loosely bound electron
from the neutral atom
is known as the

33. In Bohr’s theory of the The frequency The angular Both ‘a’ & ‘b’ None of the
hydrogen atom the of revolution momentum of above
allowed orbits for the was one of the the electron was
electron were those for frequencies an integral
which present in the multiple of
line spectrum Planck’s
constant divided
by 2

34. According to Bohr atom

only those orbits
around the nucleus are
allowed along which
angular momentum of
electron is

35. If the ionization energy 13.6 V 136 V 3.4 V None of the

of hydrogen atom is above
13.6 eV its ionization
potential will be

36. In the Bohr’s model of Infinite energy Minimum energy Maximum Zero energy
the hydrogen atom, the energy
lowest orbit
corresponds to

37. When an electron in an K.E increases, K.E. decreases, K.E increases, K.E decreases,
atom goes from a lower P.E. decreases P.E. decreases P.E. increases P.E. decreases
to a higher orbit its

38. The ratio of the kinetic 1:-1 1:2 1:1 1:-2

energy and the total
energy of the electron
in the hydrogen atom
according to Bohr’s
theory, is

39. To ionize hydrogen 13.6 ev +3.4 -13.6 ev -3.4 ev

atom from its ground
state energy required is

40. The velocity of electron N

revolving around
hydrogen nucleus is
directly proportional to
 P a g e | 16

(n=principle quantum
number)

41. According to 3rd

postulate of Bohr’s
theory:

42. The relation between

Rydberg constant (RH)
and ground state
energy (EO) is given by
the relation:

43. The energy in the 4th -2.51 eV -3.50 eV -13.6 eV 0.85 eV

orbit of hydrogen atom
is

44. The equation or

Rydberg constant is
given by

45. The radius of 10th orbit 0.053nm 0.53nm 5.3nm 53nm

in hydrogen atom is

46. If electrons jumps from 3.40eV 10.20eV 13.6 eV 3.8eV

second orbit to first
orbit in hydrogen atom
it emits photon of

TOPIC: INNER SHELL TRANSITIONS AND CHARACTERISTIC X-RAYS

No QUESTION A B C D
.

1. x-rays are deflected by Electric field Magnetic field Both ‘a’ & ‘b’ None of these

2. Which of the following K-shell L-shell M-shell N-shell

shell is closest to the
nucleus?

3. The transition of inner Low energy High energy High energy High energy
shell electrons in heavy photons or X-
atom gives rise to the rays
emission of

4. The photons emitted in particles particles particles Characteristic X-

inner shell transition rays
are called

5. The energy of X-rays Accelerating Material of Both ‘a’ & ‘b’ None of these
depends upon voltage target

6. Which of the following Infrared Ultraviolet X-rays Visible light

radiation will burn
human skin?

7. The continuous X-rays Bremsstrahlung Breaking Holography Both ‘a’ & ‘b’
spectrum is obtained
 P a g e | 17

due to radiation

8. The continuous X-rays Breaking Excitation Ionization Declaration of

spectrum is obtained potential potential potential impact electron
due to

9. The transitions of visible region Infrared region Ultraviolet All of these

lectrons in the region
hydrogen or other light
elements result in the
emission of spectral
lines in the

10. In heavy atoms, the Elliptical shells Inner shells Concentric Outer shells
electrons are assumed shells
to be arranged in

11. In the experiment of Thermonic Potential Braking Cut of current

production of X-rays, emission difference potential
electrons are
accelerated towards the
anode by

12. The maximum energy Increasing the Decreasing the Heating the None of the
of photons emitted voltage across voltage across metal target above
from an X-rays tube is the tube the tube
certain to be increased
by

13. The total energy of an Zero Negative Positive Infinity

electron in an orbit
around the nucleus is

14. When an electron To lower energy To higher Outside the To infinity

absorbs energy, it level energy levels atom
jumps

15. The total energy of an Rotational and Rotational and P.E and K.E Rotational and
electron in an orbit K.E. vibrational vibrational
around the nucleus is energy
the sum of

16. In an electronic Gamma rays Visible rays Infrared rays Ultraviolet rays
transition, atom cannot
emit

17. x-rays are similar in Alpha rays Beta rays Gamma rays None of these
nature to

18. x-rays travel in straight Less than light Greater than Equal to light Equal to sound
line with velocity light

19. The penetrating power High mass High volume High electron All of these
of X-rays is least with density density density
materials of

20. X-rays eject electrons Pair production Pair annihilation Compton effect Photoelectric
from matter by effect
 P a g e | 18

21. X-rays are part of Infrared Ultraviolet Far-ultraviolet Far-infrared

electromagnetic radiation radiation radiation radiation
spectrum and are
characterized by
frequencies higher than
those of

22. X-rays can cause Cadmium Platinocyanide Zinc sulphide All of these
fluorescence in
materials such as

23. The use fullness of X- Mass Density Penetrating All of these

rays is largely due to power
their

24. X-rays cn cause Malaria Dysentery Cancer None of these

25. Frequency of x-rays No of electrons Accelerating Nature of the Both

depends upon striking the potential target material accelerating
target potential and
nature the target
material

26. X-rays are 10-6m 10-8m 10-10m 10-12m

electromagnetic waves
having wavelength

27. A x-rays photon None of these

produced due to
transition of electron
from M-shell to K-shell
is called

28. The characteristics x- Discrete Continuous Band spectrum All of these

rays appear as discrete spectrum spectrum
lines on a

29. The continuous x-rays Bremsstrahlung Breaking Both a and b All of these
spectrum is due to an radiation radiation
effect known as

30. X-rays can cause Cancer Damage the Both a and b None of these
living tissues

31. Density differences of 2% 1% 10% 100%

the order of ----- can be
detected by the CAT-
scanners

32. In continuous x-ray K.E=hfmin

spectrum when the
electrons lose all their
K.E in the first collision,
the K.E is expressed as

33. The quality of x-rays Filament of Material of the Accelerating Both b and c
depends upon current target voltage
 P a g e | 19

34. CAT stands for Computerized Computerized Computerized None of these

axial automatic accelerated
tomography treatment tomography

35. Production of X-rays is Photo electric Compton effect Annihilation Pair production
reverse process of effect

36. In a electronic Infrared Ultraviolet Visible -radiations

transition atom cannot radiations radiations radiations
emit

37. Photons emitted in Discontinuous X- Characteristic Continuous X- Energetic X-rays

inner shell transition rays X-rays rays
are

TOPIC: UNCERTAINTY WITH IN THE ATOM

No QUESTION A B C D
.

1. The size of nucleus of an

atom is of the order of
2. An electron can never be Inside a nucleus Outside a nucleus Inside an atom All of these
found
3. The radius of the
hydrogen atom is about

4. The maximum uncertainty

in the measurement of
position of an electron
inside the nucleus is of
the order of

5. The speed of electrons in Less than speed of Greater than Equal to speed of None of these
atom is light speed of light light

TOPIC: LASER

No QUESTION A B C D
.

1. Laser is a device which Monochromatic Coherent beam An intense beam All of these
can produce beam of light of light of light
2. Lasers are classified as Solid lasers Liquid lasers Gas lasers All of these

3. Most widely used types of Neon Argon ion Helium All of these
gas lasers are

4. Operation of laser Spontaneous The existence of The existence of The existence of

depends upon emission of atoms is ground atoms is normal atoms in
radiation state state metastable state

5. Laser is a device for Producing a beam Producing a Producing a Producing highly

of white light beam of beam of high penetrating X-rays
monochromatic intensity
and coherent incoherent light
light

6. A laser beam may be Unidirectional Coherent Monochromatic Not absorbed

 P a g e | 20

used to measure very

large distance because it
is

7. Laser beam can be used Tomography Holography Both ‘a’ & ‘b’ None of these
to generate three
dimensional images of
objects in a process called

8. The ratio of life time of

metastable excited state
to the life time of normal
excited state is

9. Under lying principle of Induced Stimulated Spontaneous All

laser operation is absorption emission emission

10. Population inversion More atoms in More atoms in Equal number of All depending
means exited states ground states atoms in ground upon the type of
state and in LASER
excite

11. To diagnose diseases of Carbon laser Water laser Rubi laser Helium neon laser
the eye we use

12. Laser is the acronym for Light amplification Light Light Light amplification
by slow energy amplification by amplification by by solar energy
radiation simple energy stimulated radiation
radiation emission of
radiation

13. The excited states in Metastable state Normal state Ground state None of these
which the life time of an
electron is of the order of
sec are called

14. The most common type of Neon laser Argon laser Helium-neon None of these
lasers used in physics laser
laboratories are

15. Helium-neon laser, 10% 15% 25% 85%

discharge tube contains
helium

16. The process in which the Population Normal Induced None of these
higher state has a greater inversion population population
population than the lower
energy state is called

17. Laser can be used For welding For inducing For All of these
fusion reactions telecommunicatio
ns along optical
fibers

18. Laser beam can be used Tomography Holography Electro – graphy Xerography
to generate three
dimensional images of
objects in a process called

19. What is the colour of light Blue Green Red Yellow

emitted from He-Ne
 P a g e | 21

Laser?

20. Helium-neon laser, 10% 15% 25%` 85%

discharge tube contains
neon

21. Which is not characteristic Monochromatic Coherent Intense Multi directional

of LASER?