Work done by a force is maximum when the angle between force and displacement is MCQ with Answer and Explanation
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Question #1
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The radius of the nth Bohr orbit in hydrogen atom is proportional to:
Correct Answer: Option C
Explanation:
Bohr model: radius r_n = (4πε₀ħ²n²)/(m_e e²) = n² a₀, where a₀ is Bohr radius (≈0.529 Å). Thus r_n ∝ n². Energy E_n ∝ -1/n². Memory tip: 'Bohr radius: r ∝ n²; energy: E ∝ -1/n²'. This atomic physics formula is frequently tested in competitive exams. Always recall that n is principal quantum number; higher n means larger orbit, less tightly bound electron. This problem assesses understanding of quantization in early quantum theory.
Bohr model: radius r_n = (4πε₀ħ²n²)/(m_e e²) = n² a₀, where a₀ is Bohr radius (≈0.529 Å). Thus r_n ∝ n². Energy E_n ∝ -1/n². Memory tip: 'Bohr radius: r ∝ n²; energy: E ∝ -1/n²'. This atomic physics formula is frequently tested in competitive exams. Always recall that n is principal quantum number; higher n means larger orbit, less tightly bound electron. This problem assesses understanding of quantization in early quantum theory.
Question #2
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When a wave travels from one medium to another, which of its properties never changes?
Correct Answer: Option B
Explanation:
When a wave (like light or sound) changes mediums, its velocity changes due to the new medium's optical or mechanical density. Wavelength changes proportionally with velocity (v = fλ). However, frequency is determined solely by the source generating the wave and the energy of the photons/particles, and it remains absolutely constant.
When a wave (like light or sound) changes mediums, its velocity changes due to the new medium's optical or mechanical density. Wavelength changes proportionally with velocity (v = fλ). However, frequency is determined solely by the source generating the wave and the energy of the photons/particles, and it remains absolutely constant.
Question #3
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Stefan-Boltzmann Law states that the total radiant heat energy emitted from a perfectly black body is proportional to:
Correct Answer: Option D
Explanation:
The Stefan-Boltzmann law dictates that the total energy radiated per unit surface area of a black body across all wavelengths per unit time (Emissive Power, E) is strictly directly proportional to the fourth power of the black body's thermodynamic (absolute) temperature. E = sigma * T^4, where sigma is the Stefan-Boltzmann constant.
The Stefan-Boltzmann law dictates that the total energy radiated per unit surface area of a black body across all wavelengths per unit time (Emissive Power, E) is strictly directly proportional to the fourth power of the black body's thermodynamic (absolute) temperature. E = sigma * T^4, where sigma is the Stefan-Boltzmann constant.
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