Class 12 Physics – Daily Revision MCQ (English Medium)
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A body of mass 2 kg has a radius of gyration of 0.5 m about a given axis. What is its moment of inertia about that axis?
Chapter 1: Rotational Dynamics
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Answer: B. 0.5 kg m²
I = MK² = 2 × (0.5)² = 2 × 0.25 = 0.5 kg m².Why is the excess pressure inside a soap bubble twice that inside a liquid drop of the same radius?
Chapter 2: Mechanical Properties of Fluids
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Answer: D. A soap bubble has two free surfaces, inner and outer
A drop has one surface (excess pressure 2T/r) but a bubble film has two surfaces, so its excess pressure is 4T/r.According to Wien's displacement law, what happens to the wavelength of maximum emission (λmax) of a black body when its absolute temperature is increased?
Chapter 3: Kinetic Theory of Gases and Radiation
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Answer: A. It decreases (shifts to shorter wavelength)
λmax is inversely proportional to absolute temperature, so a hotter black body peaks at a shorter wavelength.An ideal gas expands isothermally. Which statement about this process is correct?
Chapter 4: Thermodynamics
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Answer: C. Its internal energy does not change, so the heat absorbed equals the work done (Q = W)
In an isothermal process ΔT = 0, so for an ideal gas ΔU = 0 and the first law gives Q = W.The length of a simple pendulum is made 4 times its original value at the same place. Its period of oscillation becomes:
Chapter 5: Oscillations
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Answer: B. 2 times
T = 2π√(L/g), so T ∝ √L; √4 = 2, hence the period doubles.Light in a medium of refractive index n₁ falls on the surface of a medium of refractive index n₂. The Brewster angle θB is given by:
Chapter 7: Wave Optics
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Answer: C. tan θB = n₂/n₁
Brewster's law: θB = tan⁻¹(n₂/n₁); at this angle the reflected light is completely plane polarized.The space between the plates of a parallel plate capacitor (capacitance C₀ in air) is completely filled with a dielectric of dielectric constant k. The new capacitance is:
Chapter 8: Electrostatics
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Answer: A. kC₀
When the dielectric fills the whole gap (t = d), C = kε₀A/d = kC₀, i.e. capacitance increases k times.Light of a fixed frequency above the threshold frequency falls on a metal surface. If only its intensity is increased, what happens?
Chapter 14: Dual Nature of Radiation and Matter
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Answer: D. Photoelectric current increases, but maximum kinetic energy stays the same
More intensity means more photons, so more electrons are emitted (larger current); KEmax depends only on frequency, not intensity.A radioactive sample has a half-life of 4 days. What fraction of the original nuclei remains undecayed after 12 days?
Chapter 15: Structure of Atoms and Nuclei
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Answer: B. 1/8
12 days = 3 half-lives, so the fraction left = (½)³ = 1/8.Which special purpose junction diode is commonly used in a voltage regulator circuit of a power supply?
Chapter 16: Semiconductor Devices
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Answer: C. Zener diode
A Zener diode works on junction breakdown and keeps the output voltage nearly constant, so it is used as a voltage regulator.
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All questions are written by PadhaiNotes in our own words from the chapters of the official Maharashtra State Board Balbharati textbook (ebalbharati.in). Each question shows its chapter.