Unit 2 — Introduction to Modern Physics · Physics. These are 10 questions from the Magmo3 bank on this lesson, from easy to hard. Solve each one, then open "Show answer and explanation". Magmo3 has 53 questions on this lesson, each with an explanation.
The Lyman series of the hydrogen spectrum lies entirely in the … region.
Correct answer: (C) ultraviolet
Explanation: Transitions ending at n = 1 release large photon energies, giving ultraviolet lines.
The Paschen series of hydrogen consists of the spectral lines emitted when the electron falls to the level…
Correct answer: (D) n = 3
Explanation: The Paschen series comprises all transitions ending at n = 3, lying in the infrared.
Using the relation Eₙ = -13.6/n² eV, the energy of the electron in the level n = 2 of hydrogen equals…
Correct answer: (C) -3.4 eV
Explanation: E₂ = -13.6/2² = -3.4 eV.
The energy of the photon emitted when a hydrogen electron falls from n = 2 to n = 1 equals…
Correct answer: (B) 10.2 eV
Explanation: ΔE = E₂ - E₁ = -3.4 - (-13.6) = 10.2 eV.
According to de Broglie's interpretation of Bohr's model, a stable electron orbit of radius r must satisfy…
Correct answer: (C) 2πr = nλ
Explanation: A stable orbit contains a whole number of electron wavelengths: 2πr = nλ.
The energy that a ground-state hydrogen atom must absorb to raise its electron to the level n = 3 is…
Correct answer: (A) 12.09 eV
Explanation: ΔE = E₃ - E₁ = -1.51 - (-13.6) = 12.09 eV.
A hydrogen atom is excited to the level n = 4. The maximum number of different spectral lines it can emit while returning to the ground state is…
Correct answer: (A) 6
Explanation: The number of possible lines is n(n-1)/2 = 4×3/2 = 6.
A hydrogen atom's electron moves from the orbit of radius 2.12 Å to the orbit of radius 8.48 Å (first Bohr radius = 0.53 Å, Eₙ = −13.6/n² eV). The energy of the photon absorbed equals…
Correct answer: (A) 2.55 eV
Explanation: rₙ = n²r₁ gives n = 2 (4 × 0.53) and n = 4 (16 × 0.53); ΔE = −0.85 − (−3.4) = 2.55 eV.
For the transition n = 3 → n = 2 of hydrogen, using 1/λ = R(1/nf² - 1/nᵢ²) with R = 1.1×10⁷ m⁻¹, the wavelength is approximately…
Correct answer: (B) 6.5×10⁻⁷ m
Explanation: 1/λ = R(1/4 - 1/9) = R(5/36), giving λ ≈ 6.5×10⁻⁷ m.
The energy required to ionise a hydrogen atom whose electron is already in the level n = 2 is…
Correct answer: (B) 3.4 eV
Explanation: Ionisation from n = 2 needs E_∞ - E₂ = 0 - (-3.4) = 3.4 eV.
The first 10 questions in every subject are free, each with an explanation.