CUET UG Physics Booster Test 2- Spectral Series and Duality
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QUESTION 1 OF 20
When a hydrogen atom makes a transition from the second excited state (n=3) to the ground state (n=1), what is the exact energy of the emitted photon?
QUESTION 2 OF 20
Match List I with List II regarding spectral emission observations:
| List I | List II |
|---|---|
| 1. Heated rarefied gases | a. Series of discrete bright lines |
| 2. Condensed matter and dense gases | b. Continuous distribution of wavelengths |
| 3. Atomic hydrogen | c. Set of lines with fixed relative positions |
| 4. Emission spectrum generally | d. Bright lines on a dark background |
QUESTION 3 OF 20
Incorrect statement about the absorption process and transmitted light:
QUESTION 4 OF 20
Statements regarding dark lines in atomic spectra:
1. They indicate the specific frequencies that have been absorbed by atoms of the gas.
2. They appear in the continuous spectrum when transmitted light is analysed with a spectrometer.
3. They are produced spontaneously when electrons fall to lower energy levels.
4. They form what is known as the absorption spectrum of the material.
QUESTION 5 OF 20
Because each element is associated with a characteristic spectrum of radiation, analyzing the emission line spectra of a material can serve as a type of fingerprint for gas identification, which strictly implies that:
QUESTION 6 OF 20
In Bohr's theory, which explains the unique discrete lines emitted by atomic hydrogen, the specific wavelengths can be deduced from the energy differences between allowed states. The mathematical expression for total energy Eₙ is:
QUESTION 7 OF 20
Statements about the ionisation energy of the hydrogen atom:
1. It is the minimum energy required to free the electron from the ground state.
2. Its value is exactly 13.6 eV.
3. The theoretical prediction disagrees heavily with the experimental value.
4. It corresponds to the energy required to reach n = ∞.
QUESTION 8 OF 20
When a 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature:
QUESTION 9 OF 20
When an electron falls from an excited state to the ground state (n=1), a characteristic series of lines is emitted. As the principal quantum number n of the excited state increases, the minimum energy required to subsequently free the electron _______ and the energy gap to the ground state _______.
QUESTION 10 OF 20
When analyzing transitions that drop back to lower energy states, the exact difference of energy is carried away by a photon. Since nf and ni are both restricted to integers, this mathematically ensures that:
QUESTION 11 OF 20
Incorrect statement about the wave nature of electrons:
QUESTION 12 OF 20
Statements concerning particle waves within Bohr orbits:
1. A standing wave is successfully formed only when the total orbital distance is an integral number of wavelengths.
2. The momentum p of the electron is given by mv assuming the speed is much less than light.
3. The corresponding de Broglie wavelength (λ) is equal to h/mv.
4. All fractional, continuous wavelengths form perfectly resonant standing waves.
QUESTION 13 OF 20
For an electron in a circular resonant standing wave orbit, the quantum condition linking the full orbit circumference to the electron's momentum p is:
QUESTION 14 OF 20
What specific condition ensures that an electron's wave does not quickly drop to zero amplitude due to self-interference in a circular orbit?
QUESTION 15 OF 20
Match List I with List II for the derivation of angular momentum from the de Broglie hypothesis:
| List I | List II |
|---|---|
| 1. λ | a. h/p |
| 2. 2πrₙ | b. nλ |
| 3. p | c. mv |
| 4. mvrₙ | d. nh/2π |
QUESTION 16 OF 20
Correct statements about why only certain quantised states persist without radiating:
1. Waves with non-integral wavelengths interfere with themselves and their amplitudes drop to zero.
2. The electron waves resonate, allowing the orbit to maintain dynamically stable standing waves.
3. The integer n in the angular momentum formula represents the number of full wavelengths fitting into the circumference.
4. The continuous emission spectrum matches these persistent non-radiating states exactly.
QUESTION 17 OF 20
The Bohr model is strictly applicable only to _______ atoms and entirely fails to account for the electrical forces between _______ in more complex atoms.
QUESTION 18 OF 20
If the hydrogen atom corresponds to atomic number Z = 1, what is the atomic number Z for which Bohr's model successfully predicts transition frequencies but still fundamentally fails to explain the relative intensity variations of the spectral lines?
QUESTION 19 OF 20
Statements regarding the true picture of multi-electron complex atoms:
1. It firmly requires a new and radical theory based on Quantum Mechanics.
2. A given energy state is characterised generally by four quantum numbers (n, l, m, s).
3. Bohr's single quantum number n provides a complete and flawless picture for multi-electron atoms.
4. The electron-electron electrical interaction is comparable in magnitude to the electron-nucleus electrical force.
QUESTION 20 OF 20
Incorrect statement regarding classical Bohr orbits versus modern quantum mechanics:
Test Complete!
Answer Review
1 When a hydrogen atom makes a transition from the second excited state (n=3) to the ground state (n=1), what is the exact energy of the emitted photon?
�� Energy levels in hydrogen are quantized. �� Emitted photon energy equals the difference between energy levels. �� For n=3 → n=1, a large energy gap exists.
For hydrogen: Eₙ = -13.6/n² eV E₁ = -13.6 eV E₃ = -13.6/9 = -1.51 eV Photon energy emitted: ΔE = E₃ - E₁ ΔE = (-1.51) - (-13.6) ΔE = 12.09 eV Therefore, the emitted photon has energy 12.09 eV.
- �� Option A → 10.2 eV corresponds to the n=2 transition energy from the ground state.
- �� Option C → 1.51 eV is the magnitude of the energy of the n=3 state itself.
- �� Option D → 3.40 eV is the magnitude of the n=2 state energy.
Used
- Substitution
Application:
- Substitute n=1 and n=3 into the hydrogen energy formula.
Final Logic:
- Photon energy = E₃ − E₁ = 12.09 eV.
3 → 1 gives 12.09 eV
2 Match List I with List II regarding spectral emission observations:
| List I | List II |
|---|---|
| 1. Heated rarefied gases | a. Series of discrete bright lines |
| 2. Condensed matter and dense gases | b. Continuous distribution of wavelengths |
| 3. Atomic hydrogen | c. Set of lines with fixed relative positions |
| 4. Emission spectrum generally | d. Bright lines on a dark background |
�� Rarefied gases give line spectra. �� Dense matter gives continuous spectra. �� Hydrogen has fixed spectral line positions.
List I — List II 1. Heated rarefied gases — a. Series of discrete bright lines 2. Condensed matter and dense gases — b. Continuous distribution of wavelengths 3. Atomic hydrogen — c. Set of lines with fixed relative positions 4. Emission spectrum generally — d. Bright lines on a dark background Thus, option B is correct.
- �� Options A, C and D contain incorrect pairings between radiation sources and spectral characteristics.
Used
- Option Grouping
Application:
- Match known spectrum types with their properties.
Final Logic:
- Rarefied gas → Line spectrum; Dense matter → Continuous spectrum.
Rare Gas = Lines, Dense Matter = Continuous
3 Incorrect statement about the absorption process and transmitted light:
�� Absorption requires photon intake. �� Emission occurs during downward transitions. �� Dark lines indicate absorbed frequencies.
An atom moves to a higher energy state by absorbing a photon whose energy matches the energy gap between two states. Emission occurs when an electron falls to a lower state. Therefore, option C is correct.
- �� Option A → Correct description of absorption spectra.
- �� Option B → Absorption and emission lines occur at the same wavelengths.
- �� Option D → Correct statement of photon absorption.
Used
- Elimination
Application:
- Identify the statement that reverses absorption and emission.
Final Logic:
- Higher state transition requires absorption, not emission.
Up = Absorb, Down = Emit
4 Statements regarding dark lines in atomic spectra:
1. They indicate the specific frequencies that have been absorbed by atoms of the gas.
2. They appear in the continuous spectrum when transmitted light is analysed with a spectrometer.
3. They are produced spontaneously when electrons fall to lower energy levels.
4. They form what is known as the absorption spectrum of the material.
�� Dark lines indicate absorption. �� They appear in transmitted continuous light. �� Absorption spectrum contains dark lines.
Statements 1, 2 and 4 are correct. Statement 3 is incorrect because electrons falling to lower levels produce emission lines, not absorption lines. Therefore, option A is correct.
- �� Statement 3 is incorrect.
- �� Options B, C and D include statement 3.
Used
- Statement Verification
Application:
- Check each statement using absorption spectrum concepts.
Final Logic:
- Dark lines arise from absorption, not spontaneous emission.
Dark Line = Absorbed Light
5 Because each element is associated with a characteristic spectrum of radiation, analyzing the emission line spectra of a material can serve as a type of fingerprint for gas identification, which strictly implies that:
�� Every element has unique energy levels. �� Unique energy levels produce unique spectra. �� Spectra act as fingerprints.
The characteristic emission spectrum of an element arises from transitions between its unique energy levels. Since these levels differ from element to element, the emitted wavelengths are unique. Therefore, option C is correct.
- �� Option A → Energy level spacings differ among elements.
- �� Option B → Does not explain fingerprint identification.
- �� Option D → Continuous spectra are not unique fingerprints.
Used
- Conceptual Matching
Application:
- Link spectral lines to atomic structure.
Final Logic:
- Unique energy levels → Unique spectral lines.
Unique Atom = Unique Spectrum
6 In Bohr's theory, which explains the unique discrete lines emitted by atomic hydrogen, the specific wavelengths can be deduced from the energy differences between allowed states. The mathematical expression for total energy Eₙ is:
�� Bohr derived quantized energy levels. �� Energy varies as 1/n². �� Energy is negative for bound states.
The Bohr model gives: Eₙ = -me⁴ / (8ε₀²h²n²) This formula predicts hydrogen energy levels and explains spectral lines through energy differences. Therefore, option A is correct.
- �� Option B → Incorrect dependence on constants.
- �� Option C → Positive sign is incorrect.
- �� Option D → Wrong power of mass.
Used
- Formula Recall
Application:
- Use standard Bohr energy expression.
Final Logic:
- Hydrogen energy ∝ -1/n².
Bohr Energy = Negative 1/n²
7 Statements about the ionisation energy of the hydrogen atom:
1. It is the minimum energy required to free the electron from the ground state.
2. Its value is exactly 13.6 eV.
3. The theoretical prediction disagrees heavily with the experimental value.
4. It corresponds to the energy required to reach n = ∞.
�� Ionisation removes the electron completely. �� Ground-state ionisation energy is 13.6 eV. �� Final state corresponds to n = ∞.
Statements 1, 2 and 4 are correct. Statement 3 is incorrect because Bohr's prediction agrees well with experimental results for hydrogen. Therefore, option A is correct.
- �� Statement 3 is false.
- �� Options B, C and D include statement 3.
Used
- Statement Verification
Application:
- Evaluate each statement using hydrogen energy levels.
Final Logic:
- Ionisation = n=1 → n=∞.
13.6 eV Frees Electron
8 When a 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature:
�� Excitation to n=3 requires 12.09 eV. �� Ionisation requires 13.6 eV. �� 12.5 eV is insufficient for ionisation.
Energy needed: n=1 → n=3 ΔE = 13.6(1 − 1/9) = 12.09 eV Since 12.5 eV > 12.09 eV but < 13.6 eV, excitation to n=3 is possible, but ionisation is not. Therefore, option A is correct.
- �� Option B → Ionisation requires 13.6 eV.
- �� Option C → Ground state energy does not change.
- �� Option D → Ionisation energy remains fixed.
Used
- Substitution
Application:
- Compare supplied energy with excitation and ionisation energies.
Final Logic:
- 12.09 eV < 12.5 eV < 13.6 eV.
12.09 → n=3, 13.6 → Ionisation
9 When an electron falls from an excited state to the ground state (n=1), a characteristic series of lines is emitted. As the principal quantum number n of the excited state increases, the minimum energy required to subsequently free the electron _______ and the energy gap to the ground state _______.
�� Outer states are less tightly bound. �� Ionisation energy decreases with n. �� Energy gap to ground increases.
As n increases: |Eₙ| becomes smaller. Hence ionisation energy from that level decreases. However, the difference between Eₙ and E₁ increases and approaches 13.6 eV. Therefore, option D is correct.
- �� Options A, B and C contradict hydrogen energy-level behavior.
Used
- Conceptual Analysis
Application:
- Observe behavior of Eₙ = -13.6/n².
Final Logic:
- Higher n → Easier ionisation, larger drop to ground.
Higher n = Looser Electron
10 When analyzing transitions that drop back to lower energy states, the exact difference of energy is carried away by a photon. Since nf and ni are both restricted to integers, this mathematically ensures that:
�� Energy levels are quantized. �� Only specific transitions occur. �� Photon frequencies are discrete.
Since nᵢ and nf can only take integer values, the allowed energy differences are discrete. Using: hν = Eᵢ − Ef Only specific values of ν are possible. Therefore, line spectra are produced.
- �� Option A → Contradicts Bohr model.
- �� Option B → Continuous frequencies are not predicted.
- �� Option D → Angular momentum depends on n.
Used
- Conceptual Matching
Application:
- Use quantized energy-level theory.
Final Logic:
- Discrete energy levels → Discrete frequencies.
Discrete E → Discrete ν
11 Incorrect statement about the wave nature of electrons:
�� Electron exhibits wave nature. �� Standing waves require resonance. �� Arbitrary wavelengths cannot persist.
According to de Broglie, electrons behave as matter waves. Only those wavelengths that satisfy the standing-wave condition can persist in an orbit. Waves with arbitrary wavelengths undergo destructive interference and disappear. Therefore, option D is correct.
- �� Option A → Correct statement of de Broglie's hypothesis.
- �� Option B → Correct; Davisson-Germer verified electron diffraction.
- �� Option C → Standing waves arise under resonant conditions.
Used
- Elimination
Application:
- Identify the statement violating standing-wave conditions.
Final Logic:
- Only resonant wavelengths survive.
No Resonance = No Orbit
12 Statements concerning particle waves within Bohr orbits:
1. A standing wave is successfully formed only when the total orbital distance is an integral number of wavelengths.
2. The momentum p of the electron is given by mv assuming the speed is much less than light.
3. The corresponding de Broglie wavelength (λ) is equal to h/mv.
4. All fractional, continuous wavelengths form perfectly resonant standing waves.
�� Standing waves require integral wavelengths. �� p = mv for non-relativistic motion. �� λ = h/p.
Statements 1, 2 and 3 are correct. For stable orbits: 2πr = nλ Also, p = mv λ = h/p = h/mv Statement 4 is incorrect because fractional wavelengths do not form stable standing waves. Therefore, option C is correct.
- �� Statement 4 is false.
- �� Options A, B and D include statement 4.
Used
- Statement Verification
Application:
- Check each statement using de Broglie theory.
Final Logic:
- Integral wavelengths alone survive.
Integer λ = Stable Orbit
13 For an electron in a circular resonant standing wave orbit, the quantum condition linking the full orbit circumference to the electron's momentum p is:
�� λ = h/p. �� Standing-wave condition is 2πr = nλ. �� Combine both relations.
Using: λ = h/p and 2πrₙ = nλ Substituting λ: 2πrₙ = n(h/p) Thus option A is correct.
- �� Option B → Reciprocal relation is incorrect.
- �� Option C → Incorrect derivation.
- �� Option D → Dimensionally incorrect.
Used
- Substitution
Application:
- Insert λ = h/p into standing-wave condition.
Final Logic:
- 2πr = n(h/p)
Circumference = nλ
14 What specific condition ensures that an electron's wave does not quickly drop to zero amplitude due to self-interference in a circular orbit?
�� Stable orbit requires resonance. �� Integral wavelengths fit the orbit. �� Destructive interference is avoided.
Stable standing waves occur only when: 2πr = nλ where n is an integer. This ensures constructive interference and prevents the wave amplitude from vanishing. Therefore, option B is correct.
- �� Option A → Not the general condition.
- �� Option C → Speed need not equal c.
- �� Option D → n must be an integer.
Used
- Conceptual Matching
Application:
- Apply standing-wave criterion.
Final Logic:
- Integral wavelengths produce stable resonance.
Whole λ = Whole Orbit
15 Match List I with List II for the derivation of angular momentum from the de Broglie hypothesis:
| List I | List II |
|---|---|
| 1. λ | a. h/p |
| 2. 2πrₙ | b. nλ |
| 3. p | c. mv |
| 4. mvrₙ | d. nh/2π |
�� λ = h/p. �� p = mv. �� L = mvr = nh/2π.
List I — List II 1. λ — a. h/p 2. 2πrₙ — b. nλ 3. p — c. mv 4. mvrₙ — d. nh/2π Therefore, option B is correct.
- �� Other options contain incorrect mathematical pairings.
Used
- Option Grouping
Application:
- Match standard de Broglie relations.
Final Logic:
- λ → p → Standing Wave → Quantised Angular Momentum.
λ = h/p, L = nh/2π
16 Correct statements about why only certain quantised states persist without radiating:
1. Waves with non-integral wavelengths interfere with themselves and their amplitudes drop to zero.
2. The electron waves resonate, allowing the orbit to maintain dynamically stable standing waves.
3. The integer n in the angular momentum formula represents the number of full wavelengths fitting into the circumference.
4. The continuous emission spectrum matches these persistent non-radiating states exactly.
�� Standing waves explain quantisation. �� Resonance creates stability. �� n counts wavelengths.
Statements 1, 2 and 3 are correct. Statement 4 is incorrect because stable Bohr states are associated with discrete energy levels, not a continuous emission spectrum. Therefore, option A is correct.
- �� Statement 4 is incorrect.
- �� Options B, C and D include statement 4.
Used
- Statement Verification
Application:
- Evaluate each statement using standing-wave theory.
Final Logic:
- Quantisation arises from resonance, not continuous spectra.
n = Number of Waves
17 The Bohr model is strictly applicable only to _______ atoms and entirely fails to account for the electrical forces between _______ in more complex atoms.
�� Bohr model works for one-electron systems. �� Electron-electron interactions are ignored. �� Multi-electron atoms require quantum mechanics.
Bohr's model accurately describes hydrogen and hydrogen-like ions containing a single electron. It neglects electron-electron repulsion, making it unsuitable for complex atoms. Therefore, option C is correct.
- �� Option A → Multi-electron atoms are not described accurately.
- �� Option B → Neutron interactions are not the issue.
- �� Option D → Nucleon interactions are irrelevant here.
Used
- Concept Recall
Application:
- Identify the known limitation of Bohr's theory.
Final Logic:
- Hydrogenic atoms only.
Bohr = One Electron
18 If the hydrogen atom corresponds to atomic number Z = 1, what is the atomic number Z for which Bohr's model successfully predicts transition frequencies but still fundamentally fails to explain the relative intensity variations of the spectral lines?
�� Bohr predicts hydrogen frequencies well. �� Intensity prediction remains unsuccessful. �� Limitation exists even for hydrogen.
Bohr's model successfully predicts the spectral frequencies of hydrogen (Z = 1). However, it cannot explain the relative intensities of spectral lines, even in hydrogen. Therefore, option A is correct.
- �� Options B, C and D refer to atoms where additional limitations arise.
Used
- Conceptual Analysis
Application:
- Separate frequency prediction from intensity prediction.
Final Logic:
- Hydrogen frequencies yes, intensities no.
Bohr: Position Yes, Strength No
19 Statements regarding the true picture of multi-electron complex atoms:
1. It firmly requires a new and radical theory based on Quantum Mechanics.
2. A given energy state is characterised generally by four quantum numbers (n, l, m, s).
3. Bohr's single quantum number n provides a complete and flawless picture for multi-electron atoms.
4. The electron-electron electrical interaction is comparable in magnitude to the electron-nucleus electrical force.
�� Multi-electron atoms need quantum mechanics. �� Four quantum numbers describe states. �� Electron-electron interactions are important.
Statements 1, 2 and 4 are correct. Statement 3 is incorrect because a single quantum number cannot completely describe multi-electron atoms. Therefore, option A is correct.
- �� Statement 3 is false.
- �� Options B, C and D include statement 3.
Used
- Statement Verification
Application:
- Check modern quantum mechanical description.
Final Logic:
- Complex atoms require more than n alone.
Complex Atom = Four Quantum Numbers
20 Incorrect statement regarding classical Bohr orbits versus modern quantum mechanics:
�� Exact trajectories are abandoned. �� Orbitals replace orbits. �� Probability interpretation is used.
Quantum mechanics does not permit exact electron trajectories. Instead, electrons are described by wavefunctions and probability distributions called orbitals. Therefore, option A is correct.
- �� Option B → Correct consequence of uncertainty principle.
- �� Option C → Correct description of orbitals.
- �� Option D → Correct for hydrogen-like atoms.
Used
- Elimination
Application:
- Identify the statement contradicting quantum mechanics.
Final Logic:
- Orbit ≠ Orbital.
Bohr Orbit → Quantum Orbital
