Karnataka 2nd PUC Physics Model Paper 2027 — Full Paper With Solutions

This model paper follows the official KSEAB 2nd PUC Physics pattern for 2027. Theory: 70 marks in 3 hours 15 minutes. Practical: 30 marks separately.

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Paper Structure

Section	Type	Questions	Marks
Part A	MCQ + Fill in Blanks	10	10
Part B	2-mark questions (6 of 9)	9	12
Part C	3-mark questions (6 of 9)	9	18
Part D	5-mark numericals (3 of 5)	5	15
Part E	5-mark + 3-mark questions (1 of 2)	2	8+5=... wait

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PART A — Objective (1 Mark Each)

Q1. The SI unit of electric field intensity is:

(a) N (b) N/C (c) C/m (d) V·m

Answer: (b) N/C

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Q2. The process of converting AC to DC is called:

(a) Amplification (b) Modulation (c) Rectification (d) Oscillation

Answer: (c) Rectification

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Q3. A wire of resistance R is stretched to double its length. Its new resistance is:

(a) R/2 (b) R (c) 2R (d) 4R

Answer: (d) 4R
(When length doubles, area halves. R = ρL/A → R' = ρ(2L)/(A/2) = 4R)

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Q4. The photoelectric effect proves the ________ nature of light.

Answer: Particle (quantum)

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Q5. The critical angle for total internal reflection depends on:

(a) Wavelength of light (b) Refractive index of medium (c) Intensity (d) Both a and b

Answer: (d) Both a and b

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PART B — 2-Mark Questions (Attempt 6 of 9)

Q6. State Coulomb's Law. Write its mathematical form.

Answer: The electrostatic force between two point charges is directly proportional to the product of the charges and inversely proportional to the square of the distance between them.
F = kq₁q₂/r²
where k = 9×10⁹ N·m²/C², q₁, q₂ are charges, r is distance between them.

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Q7. What is meant by threshold frequency in photoelectric effect?

Answer: The minimum frequency of incident light below which no photoelectric emission occurs, regardless of the intensity of light, is called the threshold frequency (ν₀).
Below ν₀ — no electrons emitted even with very bright light.
Above ν₀ — electrons are emitted even with dim light.

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Q8. State Lenz's Law.

Answer: The direction of the induced current is such that it opposes the change in magnetic flux that causes it.
Lenz's Law is a consequence of the law of conservation of energy.
If it were not so, energy would be created from nothing — which is impossible.

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Q9. Define electric potential. Write its SI unit.

Answer: Electric potential at a point is defined as the work done per unit positive charge in bringing a test charge from infinity to that point.
V = W/q
SI unit: Volt (V) = Joule/Coulomb
Potential is a scalar quantity.

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Q10. What is a p-n junction diode? Mention its two types of biasing.

Answer: A p-n junction diode is formed by joining p-type and n-type semiconductors together. A depletion layer forms at the junction.
Two types of biasing:

1. Forward bias — p-type connected to +ve terminal; depletion layer narrows; current flows
2. Reverse bias — p-type connected to −ve terminal; depletion layer widens; no current flows

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PART C — 3-Mark Questions (Attempt 6 of 9)

Q11. Derive the expression for the equivalent resistance of resistors connected in parallel.

Answer:
Let R₁, R₂, R₃ be resistors connected in parallel with potential difference V across each.

Current through each: I₁ = V/R₁, I₂ = V/R₂, I₃ = V/R₃

Total current: I = I₁ + I₂ + I₃
V/Req = V/R₁ + V/R₂ + V/R₃

Dividing by V:
1/Req = 1/R₁ + 1/R₂ + 1/R₃

The equivalent resistance in parallel is always less than the smallest individual resistance.

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Q12. Explain the working principle of a transformer. Derive the turns ratio equation.

Answer:
Principle: Mutual induction — changing current in primary coil induces EMF in secondary coil through changing magnetic flux.

Working:

• AC supply to primary coil (Np turns)
• Alternating magnetic flux created in iron core
• Flux links with secondary coil (Ns turns)
• EMF induced in secondary: Es = −Ns(dΦ/dt)
• Primary EMF: Ep = −Np(dΦ/dt)

Turns Ratio: Ep/Es = Np/Ns
Vs/Vp = Ns/Np

• Step-up transformer: Ns > Np → Vs > Vp
• Step-down transformer: Ns < Np → Vs < Vp

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Q13. State and explain Huygen's Principle of wave propagation.

Answer:
Huygens' Principle:

1. Every point on a given wavefront acts as a source of secondary wavelets which spread out in all directions with the speed of the wave
2. The new wavefront at any later time is the forward envelope (tangent) of all the secondary wavelets

Explanation:
If AB is a plane wavefront at time t=0, each point on AB sends out secondary wavelets of radius ct (where c = speed of light).
The tangent drawn to all these spheres gives the new wavefront A'B' at time t.

This principle explains reflection, refraction, and diffraction of waves.

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PART D — 5-Mark Numericals (Attempt 3 of 5)

Q14. A parallel plate capacitor has plates of area 6×10⁻³ m² separated by 3 mm of air. Find: (i) Capacitance (ii) Charge if V = 100V (iii) Energy stored.

Solution:
ε₀ = 8.85 × 10⁻¹² F/m

(i) C = ε₀A/d = (8.85×10⁻¹²×6×10⁻³) / (3×10⁻³)
C = 17.7×10⁻¹² F = 17.7 pF

(ii) Q = CV = 17.7×10⁻¹² × 100 = 1.77×10⁻⁹ C = 1.77 nC

(iii) E = ½CV² = ½×17.7×10⁻¹²×(100)²
E = ½×17.7×10⁻¹²×10⁴ = 8.85×10⁻⁸ J

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Q15. Light of wavelength 5000 Å falls on a metal with work function 1.9 eV. Find: (i) Energy of photon (ii) Maximum KE of emitted electrons (iii) Stopping potential.

Solution:
h = 6.63×10⁻³⁴ J·s; c = 3×10⁸ m/s; λ = 5×10⁻⁷ m; 1eV = 1.6×10⁻¹⁹ J

(i) E = hc/λ = (6.63×10⁻³⁴×3×10⁸)/(5×10⁻⁷)
E = 3.978×10⁻¹⁹ J = 2.49 eV

(ii) KEmax = E − W₀ = 2.49 − 1.9 = 0.59 eV = 9.44×10⁻²⁰ J

(iii) eV₀ = KEmax → V₀ = 0.59/1 = 0.59 V

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Practice Problems (Self Test)

1. Three resistors 2Ω, 3Ω, 6Ω are connected in parallel. Find equivalent resistance and total current when 12V is applied.
2. A transformer has 500 turns in primary and 2500 turns in secondary. If primary voltage is 220V, find secondary voltage.
3. An electron moves with velocity 10⁶ m/s in a magnetic field of 0.5T perpendicular to it. Find the radius of circular path.

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Chapter-Wise Weightage

Chapter	Marks
Electrostatics	9
Current Electricity	8
Magnetism	8
Electromagnetic Induction and AC	8
Optics	10
Modern Physics	8
Semiconductor Devices	7
Communication Systems	4
Electromagnetic Waves	3

Tip: Karnataka 2nd PUC awards 5 marks for each numerical in Part D. Always write the formula first, substitute values with units, and box your final answer — this ensures full marks even if arithmetic has a small error.