Atomic Spectra MCQs
The spectral series of the hydrogen atom that lies in the ultraviolet region of the electromagnetic spectrum is called the:
Balmer series
Lyman series
Paschen series
Brackett series
According to Bohr's atomic model, the angular momentum of an electron in a stationary orbit is:
Directly proportional to the principal quantum number, n
Inversely proportional to the principal quantum number, n
Directly proportional to the square of the principal quantum number, n²
Constant for all orbits
The transition of an electron from n=4 to n=2 in a hydrogen atom results in the emission of a photon in which series?
Lyman series
Paschen series
Balmer series
Pfund series
The phenomenon where an excited atom emits a photon without any external trigger is known as:
Stimulated emission
Spontaneous emission
Absorption
Population inversion
The production of characteristic X-rays is a result of:
The rapid deceleration of high-speed electrons by a target nucleus.
Electron transitions between the inner shells of a heavy atom.
The heating of a filament in an X-ray tube.
The photoelectric effect.
For laser action to occur, a necessary condition is that there are more atoms in a higher energy state than in a lower one. This condition is called:
Metastable state
Spontaneous emission
Optical pumping
Population inversion
The energy of an electron in the nth orbit of a hydrogen atom is proportional to:
Which of the following properties is NOT characteristic of laser light?
Coherent
Monochromatic
Incoherent
Directional
The minimum energy required to remove an electron from an atom in its ground state is known as:
Excitation energy
Binding energy
Ionization energy
Work function
The Paschen series of the hydrogen spectrum is in which region?
Ultraviolet
Visible
Infrared
X-ray
For an electron in a stationary Bohr orbit, its total energy is -3.4 eV. What is its kinetic energy (KE)?
-3.4 eV
+3.4 eV
-6.8 eV
+6.8 eV
The continuous spectrum of X-rays is produced due to:
Electron transitions between discrete energy levels.
The deceleration of bombarding electrons by the target.
The excitation of the target atoms.
Thermionic emission from the filament.
A state in which an excited atom can stay for a relatively long time (e.g., 10⁻³ s) is called a:
Ground state
Excited state
Ionized state
Metastable state
The radius of the first Bohr orbit for the hydrogen atom is r₁. The radius of the third Bohr orbit is:
An absorption spectrum is characterized by:
Bright lines on a dark background.
Dark lines on a bright background.
A continuous band of colors.
No lines at all.
In a He-Ne laser, the process of exciting Ne atoms through collisions with excited He atoms is called:
Stimulated emission
Optical pumping
Resonant energy transfer
Spontaneous absorption
The series limit of a spectral series corresponds to an electron transition from:
n = 2 to n = 1
n = ∞ to the final state n.
n = (n_final + 1) to n_final
n = 1 to n = ∞
The energy of a photon emitted from a hydrogen atom is 10.2 eV. This corresponds to a transition from:
n = 2 to n = 1
n = 3 to n = 1
n = 3 to n = 2
n = 4 to n = 2
Rydberg's constant (R) is a physical constant related to:
The charge of an electron
The speed of light
Atomic spectra
Planck's constant
The process of supplying energy to the atoms of a laser medium to achieve population inversion is called:
Amplification
Coherence
Pumping
Emission
Calculate the wavelength of the second line of the Balmer series for the hydrogen atom. (Rydberg constant R_H ≈ 1.097 × 10⁷ m⁻¹)
The wavelength of characteristic X-rays depends on:
The accelerating voltage in the X-ray tube.
The material of the target anode.
The temperature of the filament.
The pressure inside the X-ray tube.
The lines in the Balmer series of the hydrogen spectrum are formed by electron transitions from higher energy levels to:
The lifetime of an atom in an ordinary excited state is typically about:
An electron in a hydrogen atom jumps from n=3 to n=1. The number of possible spectral lines that can be emitted is:
Bohr's model of the atom successfully explained:
The spectrum of all atoms and molecules.
The line spectrum of the hydrogen atom.
The Zeeman effect (splitting of spectral lines in a magnetic field).
The relative intensities of spectral lines.
In the process of stimulated emission, the emitted photon is identical to the incident photon in all aspects EXCEPT:
Frequency
Phase
Direction of travel
It is identical in all aspects mentioned.
The Brackett series in the hydrogen spectrum is formed by electron transitions ending at which energy level?
The ground state energy of a hydrogen atom is -13.6 eV. What is the energy of the first excited state?
-13.6 eV
-6.8 eV
-3.4 eV
-1.51 eV
The concept of discrete energy levels in an atom was first introduced by:
J.J. Thomson
Ernest Rutherford
Niels Bohr
Max Planck
The velocity of an electron in the first Bohr orbit is v₁. The velocity in the second orbit would be:
The shortest wavelength in the Balmer series corresponds to a transition from:
n = 3 to n = 2
n = 2 to n = 1
n = ∞ to n = 2
n = ∞ to n = 1
The laser used in barcode scanners is typically a:
CO2 laser
Ruby laser
He-Ne laser
Excimer laser
According to Bohr's third postulate, an electron emits a photon when it:
Jumps from a lower energy orbit to a higher one.
Jumps from a higher energy orbit to a lower one.
Revolves in a stationary orbit.
Is removed from the atom.
The Pfund series of the hydrogen spectrum lies in the:
Visible region
Ultraviolet region
Far-infrared region
X-ray region
What is the energy required to ionize a singly ionized helium atom (He⁺)?
13.6 eV
27.2 eV
54.4 eV
122.4 eV
A collection of atoms is bombarded with electrons. The resulting spectrum will most likely be:
An emission line spectrum
An absorption line spectrum
A continuous spectrum
A band spectrum
The ratio of the longest wavelength of the Lyman series to the longest wavelength of the Balmer series is:
One of the major failings of the Rutherford atomic model was its inability to explain:
The existence of a nucleus.
The scattering of alpha particles.
The stability of the atom.
That most of the atom is empty space.
The total energy of an electron in a stationary orbit is negative. This indicates that:
The electron is free from the nucleus.
The electron is bound to the nucleus.
The kinetic energy of the electron is negative.
The potential energy of the electron is positive.
The minimum accelerating potential required to produce X-rays of wavelength λ is given by:
V = hλ/e
V = ec/hλ
V = hc/eλ
V = h/eλ
In stimulated absorption, an atom in the ground state absorbs a photon and moves to an excited state. This is the reverse process of:
Spontaneous emission
Stimulated emission
Population inversion
Ionization
Which transition in a hydrogen atom emits a photon with the highest frequency?
n = 2 to n = 1
n = 6 to n = 2
n = 2 to n = 6
n = ∞ to n = 1
Sound waves
Electromagnetic radiation
Beta particles
Alpha particles
The 'pumping' mechanism in a ruby laser is:
Electrical discharge
Chemical reaction
Optical pumping
Atomic collisions
As the principal quantum number 'n' increases, the difference in energy between consecutive orbits:
Increases
Decreases
Remains constant
Becomes zero
The fact that each element has a unique line spectrum can be used for:
Determining the temperature of a star.
Identifying the chemical composition of a substance.
Measuring the speed of light.
Proving the existence of the ether.
According to de Broglie's hypothesis, the reason for an electron remaining in a stable orbit is that the circumference of the orbit must be:
Equal to its de Broglie wavelength.
An integral multiple of its de Broglie wavelength.
Inversely proportional to its mass.
Half the de Broglie wavelength.
An X-ray tube operates with an accelerating potential of 50 kV. What is the minimum wavelength (cutoff wavelength) of the continuous X-ray spectrum produced?
0.025 nm
0.25 nm
2.5 nm
25 nm
If an electron in a hydrogen atom is in the n=4 state, what is the maximum number of unique spectral lines that can be emitted as it transitions to lower energy levels?
According to Moseley's Law, if the atomic number (Z) of the target anode in an X-ray tube is increased, the frequency of the characteristic X-rays:
Increases
Decreases
Remains the same
Becomes zero
A four-level laser system is more efficient than a three-level system primarily because:
It uses a more powerful pumping source.
It can produce four different colors of light.
The metastable state has a longer lifetime.
Population inversion is easier to achieve.
What is the ratio of the radius of the second Bohr orbit (n=2) to the radius of the fourth Bohr orbit (n=4) in a hydrogen atom?
Which of the following phenomena could NOT be explained by Bohr's atomic model?
The spectrum of a hydrogen atom
The Zeeman effect (splitting of spectral lines in a magnetic field)
The stability of an atom
The spectrum of a He⁺ ion
What is the function of the resonant cavity (mirrors) in a laser?
To create the initial population inversion.
To reflect photons back and forth through the medium for amplification.
To absorb unwanted wavelengths of light.
To cool the laser medium.
The penetration power of X-rays is high because they have:
High speed
No charge
Short wavelength and high energy
Long wavelength and low energy
The first line of the Paschen series results from the transition:
n = 3 to n = 2
n = 4 to n = 3
n = 2 to n = 1
n = ∞ to n = 3
The concept of a central positive nucleus was a conclusion from:
The photoelectric effect experiment.
The alpha particle scattering experiment.
The analysis of the hydrogen spectrum.
The discovery of the electron.
In a three-level laser system, the lasing transition occurs between the metastable state and:
The ground state
An intermediate state above the ground state
A higher excited state
Another metastable state
The color of light emitted in the Balmer series with the longest wavelength is:
Violet
Blue-Green
Red
Yellow
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