Structure of Atoms and Nuclei — Flashcards
Maharashtra Board · Class 12 · Physics
24 flashcards for Structure of Atoms and Nuclei (Maharashtra Board Class 12 Physics) to test yourself on key terms and facts.
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What was Thomson's atomic model and why was it called the 'plum-pudding model'?
Answer
Thomson's atomic model (1903) proposed that an atom is a sphere with uniform positive charge in which negatively charged electrons are embedded like plums in a pudding. The total positive charge equal…
In the Geiger-Marsden experiment, what percentage of alpha particles were scattered through angles larger than 90°?
Answer
Only about one alpha particle in 8000 (0.0125%) was deflected through angles larger than 90°. Most alpha particles (99.86%) passed straight through the gold foil with negligible deflection. Only 0.14%…
What are the three main difficulties with Rutherford's atomic model?
Answer
1) According to Maxwell's equations, orbiting electrons should continuously emit electromagnetic radiation and lose energy. 2) The electron should spiral into the nucleus causing atomic collapse. 3) T…
What is the Rydberg formula for hydrogen spectrum and what do the variables represent?
Answer
1/λ = RH(1/n² - 1/m²), where λ is wavelength of spectral line, RH = 1.097 × 10⁷ m⁻¹ is Rydberg constant, n = 1,2,3... for Lyman, Balmer, Paschen series respectively, and m takes integral values greate…
State Bohr's three postulates for his atomic model.
Answer
1) Electrons revolve around nucleus in circular orbits with centripetal force provided by electrostatic attraction. 2) Angular momentum of electron is quantized: mvr = nh/2π, where n is principal quan…
Calculate the radius of the 3rd orbit of electron in hydrogen atom. (Given: Bohr radius a₀ = 0.053 nm)
Answer
Using the formula rn = a₀n², where a₀ = 0.053 nm is the Bohr radius: r₃ = a₀ × 3² = a₀ × 9 = 0.053 × 9 = 0.477 nm The general formula is rn = (n²h²ε₀)/(πmeZe²) for hydrogen-like atoms, which simplifi…
What is the energy of an electron in the nth orbit of hydrogen atom? What is the ground state energy?
Answer
En = -13.6Z²/n² eV. For hydrogen (Z=1): En = -13.6/n² eV. Ground state (n=1): E₁ = -13.6 eV First excited state (n=2): E₂ = -3.4 eV Second excited state (n=3): E₃ = -1.51 eV Negative energy indicate…
A Rutherford scattering problem: An alpha particle with 28.33 MeV energy stops at the surface of a gold nucleus. What is the distance of closest approach?
Answer
When the alpha particle stops, all kinetic energy converts to potential energy: K = (1/4πε₀) × (Zαe)(ZAue)/r For gold: ZAu = 79, Zα = 2 Using K = 9×10⁹ × (2×79×(1.6×10⁻¹⁹)²)/r 28.33 MeV = 28.33 × 1.6…
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