2nd Year Physics - 30 Most Important Conceptual Questions

 

12th Physics Conceptual Questions

PHYSICS 12th Federal Board
(30 CONCEPTUAL QUESTIONS) 

Following 30 Conceptual Questions are the Guess for Physics Numerical in Federal Board. Sample Questions have been provided with relevant topics and being a student you can get detailed answer from any AI Platform (like ChatGPT, Deepseek, Gemini or Meta AI), just copy the question and past it there. So, Important thing is to develop your understanding regarding SLO based exams compromised which types of Questions.

To watch Details Explanation of each topic: Click Here

• The Electric Potential is constant through a given region, is the electric field zero or non-zero?

If the electric potential V is constant in a region, the electric field E is given by E = -∇V. Since the gradient of a constant is zero, E = 0. Example: Inside a charged conductor, V is constant and E = 0.

• Can different equipotential lines cross each other? Explain.

Equipotential lines represent locations with the same electric potential. If two lines crossed, a point would simultaneously have two different potentials, which is physically impossible. Formula: V = constant per line. Example: Concentric circles around a point charge are non-intersecting equipotential lines.

• Water has a large dielectric constant but rarely used in capacitors. Why?

Water has a high dielectric constant, which should be ideal for capacitors. However, it is a polar solvent and conducts electricity due to dissolved ions, causing leakage currents or dielectric breakdown. Formula: C = ε₀A/d.

• Under what circumstances can terminal P.D. of a battery exceeds EMF?

The terminal voltage of a battery is V = ε - Ir during discharge, and V = ε + Ir during charging. So during external charging, terminal voltage can exceed the EMF. Example: A 12V battery being charged at 2A with r = 1Ω gives V = 14V.

• Determine KVL is based on conservation of energy while KCL is based on conservation of charge?

KVL is based on energy conservation: total work done around a closed loop is zero. KCL is based on charge conservation: net current entering a node equals current leaving. Formula: KVL: ∑V = 0 or ∑E=∑V, KCL: ∑I_in = ∑I_out.

• How much charge will flow in a pocket calculator each minute when current is 0.0001A?

Charge Q = It. For I = 0.0001 A, t = 60 s, Q = 0.0001 × 60 = 0.006 C. Example: 0.006 Coulombs is equal to about 3.75 × 10^16 electrons flowing per minute.

• Electron and proton are projected with same velocity normal to magnetic field? Which one suffer more deflection?

In a magnetic field B, a particle's deflection radius is r = mv/qB. Electrons have much less mass than protons, so they curve more under the same B. Example: In a CRT, electrons sharply curve due to small mass.

• If a current passes through an unstretched spring, will it contract or expand?

A current in a helical spring creates a magnetic field along its axis. The Lorentz force causes the coils to attract each other, leading to contraction. Formula: Force per unit length F = μ₀I²/2πr. Example: Used in magnetic actuators.

• How can neutron is being accelerated in a cyclotron?

Neutrons cannot be accelerated in a cyclotron because they have no electric charge. Cyclotrons use electric and magnetic fields to accelerate charged particles, but since neutrons are neutral, they do not respond to these fields. Instead, neutrons are typically produced in nuclear reactions and directed using mechanical or magnetic means.

• Show that the relationship E = -ΔΦ/Δt is dimensionally correct?

The induced EMF E = -ΔΦ/Δt. Dimensional check: [E] = [Wb/s] = [V] = [ML²T⁻³A⁻¹], which matches. Conclusion: The relation is dimensionally consistent and physically valid.

• Give the formula of flux linkage in terms of angular orientation?

Magnetic flux linkage is Φ = NBAcosθ, where θ is the angle between the magnetic field and area vector. Example: A coil rotating in a magnetic field induces maximum EMF when θ changes rapidly.

• How Eddy current can be minimized in transformer?

Eddy currents are loops of induced current in conductors due to changing magnetic fields. To minimize them, transformer cores are laminated, reducing area for loops. Formula: Power loss P = I²R. Example: Iron cores are laminated to reduce heating.

• How does doubling the frequency affect the reactance of (a) inductor (b) capacitor?

(a) Inductive reactance XL = 2πfL: doubling f doubles XL. (b) Capacitive reactance XC = 1/2πfC: doubling f halves XC. Example: In AC circuits, frequency shift alters current flow significantly.

• If the peak Value of a sine wave is 1000 V, what is its effective (Veff) value?

The RMS or effective value of a sine wave is Vrms = Vpeak/√2. For 1000V peak: Vrms = 1000/√2 ≈ 707V. Example: Household AC is typically 220V RMS, not peak.

• Discuss the superconductivity of material with the help of graph?

Superconductivity occurs when resistance drops to zero below critical temperature Tc. Graph: R vs T drops abruptly at Tc. Example: Mercury becomes superconducting below 4.2K, allowing lossless current flow.

• What is the difference between Elastic deformation and plastic deformation?

Elastic deformation is temporary and follows Hooke’s Law: F = kx. Plastic deformation is permanent and occurs beyond yield strength. Example: A stretched rubber band is elastic; bent metal beyond limit is plastic.

• Distinguish between Soft and Hard substances by drawing its curves?

Stress–strain curves: Soft materials show shallow slope, low yield point. Hard materials have steep slope, high stress before yielding. Example: Lead is soft; steel is hard and resists deformation.

• How can conductivity of semiconductor be raised?

Conductivity σ = nqμ increases by: (1) Doping: adds carriers (e.g., Phosphorus in Si), (2) Temperature: in intrinsic semiconductors, thermal energy increases free carriers. Example: Silicon doped with Boron becomes a P-type conductor.

• Why the base current is weak compared to collector current?

Base current IB is small; it controls large collector current IC. Gain: β = IC/IB, typically 100–200. Example: In switching, a tiny base signal triggers high-power output.

• A P-type semiconductor has large number of holes but still electrically neutral. Why?

P-type has excess holes, but the number of added acceptor atoms equals missing electrons. Total charge remains balanced, making the material electrically neutral. Example: Doping Si with Boron introduces holes but no net charge.

• Why transistor is called current amplification device?

A transistor amplifies current: small base current modulates large collector current. Formula: IC = βIB. Example: In audio amplifiers, microampere-level base signals drive milliampere outputs.

• Differentiate between NPN and PNP transistors?

NPN transistor: electrons flow from emitter to collector; requires positive base. PNP transistor: holes flow; base must be negative. Example: NPN used in digital circuits; PNP in complementary designs.

• How would everyday events appear to us, if c= 50 m/s?

If c = 50 m/s, then walking (~1 m/s) becomes 2% of c. Time dilation t = t₀/√(1 - v²/c²) becomes noticeable in daily life. Example: Clocks would tick slower for fast-moving vehicles.

• Why must the rest mass of photon be zero?

Photon travels at speed c. If it had mass, relativity predicts infinite energy at c, which is unphysical. Thus, photon rest mass must be zero. Formula: E = pc for massless particles.

• Why don't we observe the Compton's effect with visible light?

Compton shift: Δλ = (h/m(e)c)(1 - cosθ). For visible light (λ ~ 500 nm), shift is negligible. Example: X-rays show measurable shift; visible light does not.

• Calculate the shortest and longest wavelength of the radiation for the Paschen series?

Paschen series: n(1) = 3. Shortest λ: n(2) = ∞ → λ ≈ 820 nm. Longest: n2 = 4 → λ ≈ 1875 nm. These fall in the infrared region of the spectrum.

• Calculate the shortest wavelength produced by an X-ray is 0.46 nm, What is the voltage applied?

V = hc/eλ = (6.63×10⁻³⁴×3×10⁸)/(1.6×10⁻¹⁹×0.46×10⁻⁹) ≈ 2700 V. Example: This is typical for high-voltage X-ray tubes.

• Why heavier nuclei have more neutrons than protons?

Heavy nuclei need more neutrons to counteract proton repulsion via the strong force. Neutrons increase nuclear binding energy without adding charge. Example: Lead-208 has 126 neutrons and 82 protons for stability.

• Why are small and large nuclei unstable?

Small nuclei (e.g., H-1) have insufficient binding per nucleon; large ones (e.g., U-238) have high Coulomb repulsion. 

Result: Both may decay to more stable nuclei.

• Why is a conventional fission nuclear reactor not able to explode as a bomb?

Fission reactors use low-enriched uranium and have control rods to absorb neutrons. They lack critical mass and geometry to cause rapid, explosive chain reactions. Example: Reactors release energy over hours, not microseconds.

• Why does the fusion of light nuclei into heavier nuclei release energy?

Fusion of light nuclei (like H) releases energy because total mass after fusion is less than before. Formula: E = Δmc². Example: Sun fuses hydrogen to helium, powering its radiance.

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