Atomic and Nuclear physics — Flashcards
Tamil Nadu Board · Class 12 · Physics
25 flashcards for Atomic and Nuclear physics (Tamil Nadu Board Class 12 Physics) to test yourself on key terms and facts.
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What is specific charge (e/m) of an electron and how was it determined in J.J. Thomson's experiment?
Answer
Specific charge is the charge per unit mass of an electron. Value: e/m = 1.7 × 10¹¹ C/kg In Thomson's experiment: • Cathode rays passed through crossed electric (E) and magnetic (B) fields • When fo…
In Millikan's oil drop experiment, a negatively charged oil drop of mass 1.6 × 10⁻¹⁵ kg is suspended in an electric field of 1000 V/cm. Find the charge on the drop. (g = 10 m/s²)
Answer
Given: m = 1.6 × 10⁻¹⁵ kg, E = 1000 V/cm = 10⁵ V/m, g = 10 m/s² At equilibrium, electric force balances weight: qE = mg Step 1: Calculate gravitational force F_g = mg = 1.6 × 10⁻¹⁵ × 10 = 1.6 × 10⁻¹…
Compare J.J. Thomson's, Rutherford's, and Bohr's atom models. What was the main drawback of each?
Answer
Thomson's Model (Watermelon Model): • Positive charge uniformly distributed with electrons embedded • Drawback: Could not explain atom stability; violated Earnshaw's theorem Rutherford's Model (Nucle…
What is angular momentum quantization in Bohr's atom? Write the condition and explain its significance.
Answer
Angular Momentum Quantization: Condition: L = mvr = nℏ = n(h/2π) Where: • L = angular momentum • m = electron mass • v = electron velocity • r = orbital radius • n = principal quantum number (1, 2, 3…
Calculate the radius of the 3rd Bohr orbit in hydrogen atom. (Bohr radius a₀ = 0.529 Å)
Answer
Given: n = 3, a₀ = 0.529 Å = 0.529 × 10⁻¹⁰ m, Z = 1 (hydrogen) Formula: r_n = (a₀ × n²)/Z Step 1: Substitute values r₃ = (0.529 × 3²)/1 Å r₃ = (0.529 × 9) Å r₃ = 4.761 Å Step 2: Convert to meters r…
Find the velocity of electron in the ground state of hydrogen atom. Express as a fraction of the speed of light. (c = 3 × 10⁸ m/s)
Answer
Formula: v_n = (αcZ)/n where α = fine structure constant = 1/137 For hydrogen ground state: n = 1, Z = 1 Step 1: Calculate velocity v₁ = (c × 1)/(137 × 1) v₁ = (3 × 10⁸)/137 v₁ = 2.19 × 10⁶ m/s Ste…
Calculate the excitation energy needed to move an electron from n=1 to n=3 in a hydrogen atom.
Answer
Formula: ΔE = E_f - E_i = -13.6 Z²(1/n_f² - 1/n_i²) eV Given: Z = 1 (hydrogen), n_i = 1, n_f = 3 Step 1: Calculate final and initial energies E₁ = -13.6 × 1²/1² = -13.6 eV E₃ = -13.6 × 1²/3² = -13.6…
What is the ionization energy of hydrogen atom? Explain why it has a specific value.
Answer
Ionization Energy (from ground state): E_ionization = E_∞ - E₁ = 0 - (-13.6 eV) = 13.6 eV General Formula: E_ion = 13.6 Z²/n² eV Why this specific value: 1. Energy Zero Reference: Zero energy is as…
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