A ship floats because its density is MCQ with Answer and Explanation
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Question #1
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A body at 100°C is placed in contact with a body at 0°C. Heat flow stops when
Question #2
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The work function of a metal is 2.3 eV. The threshold frequency for photoelectric emission is approximately: (h = 4.14×10⁻¹⁵ eV·s)
Correct Answer: Option C
Explanation:
Photoelectric equation: work function φ = hν₀, where ν₀ is threshold frequency. Thus ν₀ = φ/h = 2.3 eV / (4.14×10⁻¹⁵ eV·s) ≈ 5.555×10¹⁴ Hz ≈ 5.6×10¹⁴ Hz. This direct application tests photoelectric effect fundamentals. Memory aid: 'ν₀ = φ/h; higher work function ⇒ higher threshold frequency'. Competitive exams frequently provide h in eV·s for such calculations. Always ensure units match: eV for φ and h to avoid conversion errors. This problem assesses numerical proficiency in modern physics applications.
Photoelectric equation: work function φ = hν₀, where ν₀ is threshold frequency. Thus ν₀ = φ/h = 2.3 eV / (4.14×10⁻¹⁵ eV·s) ≈ 5.555×10¹⁴ Hz ≈ 5.6×10¹⁴ Hz. This direct application tests photoelectric effect fundamentals. Memory aid: 'ν₀ = φ/h; higher work function ⇒ higher threshold frequency'. Competitive exams frequently provide h in eV·s for such calculations. Always ensure units match: eV for φ and h to avoid conversion errors. This problem assesses numerical proficiency in modern physics applications.
Question #3
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What is the magnetic dipole moment of an electron revolving in a circular orbit of radius 'r' with a uniform speed 'v'?
Correct Answer: Option B
Explanation:
Magnetic dipole moment M = Current(I) * Area(A). Current is charge/time: I = e / T. Time period T = 2pir / v. So I = ev / (2pir). The area of the circular orbit is A = pir^2. Therefore, M = [ev / (2pir)] * [pir^2] = evr / 2. This is a standard derivation in modern physics.
Magnetic dipole moment M = Current(I) * Area(A). Current is charge/time: I = e / T. Time period T = 2pir / v. So I = ev / (2pir). The area of the circular orbit is A = pir^2. Therefore, M = [ev / (2pir)] * [pir^2] = evr / 2. This is a standard derivation in modern physics.
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