GUJCET Physics: 40 MCQs, Formula-First Reasoning
GUJCET Physics is a common subject in both PCM and PCB combinations: 40 single-correct MCQs, 1 mark each, with 0.25 deducted for a wrong response. Questions follow the GSEB Class 12 Science syllabus, so the highest-yield areas are electrostatics, current electricity, ray and wave optics, EMI/AC, dual nature, atoms/nuclei and semiconductors. The paper is numerical but compact: most items need one relation and one unit check, not a long derivation.
Core rules to keep ready
- Capacitors: charge is conserved when isolated conductors are connected; common potential V = (C₁V₁ + C₂V₂)/(C₁ + C₂). Energy is lost to heat/radiation unless the problem says otherwise.
- Circuits: terminal voltage V = ε − Ir; an ideal voltmeter has infinite resistance, an ideal ammeter zero resistance.
- Optics: use the Cartesian sign convention consistently; lens power P = 1/f (metres). Total internal reflection requires dense-to-rare travel and an angle above the critical angle.
- AC: I_rms = I_peak/√2; average current over a full cycle is zero; reactance X_L = ωL, X_C = 1/(ωC).
- Modern physics: photon energy E = hc/λ; photoelectric threshold ν₀ = φ/h; activity halves every half-life.
Worked example
A 2 μF capacitor charged to 100 V is connected to an uncharged 4 μF capacitor. Find the common potential and energy lost. Initial charge Q = C₁V₁ = 2×10⁻⁶ × 100 = 2×10⁻⁴ C. After connection, Q is shared: V = Q/(C₁+C₂) = 2×10⁻⁴/(6×10⁻⁶) = 33.3 V. Initial energy U_i = ½C₁V₁² = ½×2×10⁻⁶×10⁴ = 0.010 J. Final U_f = ½×6×10⁻⁶×(33.3)² ≈ 0.00333 J. Loss ≈ 6.7×10⁻³ J. The missing energy is not a calculation error: it is dissipated in the connecting wire.
Traps that cost marks
- An n-type semiconductor is electrically neutral, not negatively charged.
- Do not mix rms and peak values in power calculations.
- Induced emf depends on the rate of change of flux, not on flux itself.
- Convert cm, mm and μF to SI before substituting.
- A wrong answer costs 0.25; if two options remain, the expected value of a guess is negative.