Board-style MCQs and past-paper numericals in the BIEK / Sindh Board pattern. Tap an option to check yourself instantly. Solved questions are at the bottom.
Multiple-choice questions
Solved numericals (past papers)
Charge of a proton from its quark content
A proton is made of two up quarks (each +2/3 e) and one down quark (−1/3 e). Find its charge.
q = (+2/3) + (+2/3) + (−1/3) = +3/3 = +1 e
Charge of a neutron from its quark content
A neutron is made of one up quark (+2/3 e) and two down quarks (each −1/3 e). Find its charge.
q = (+2/3) + (−1/3) + (−1/3) = 0 ⇒ 0 (neutral)
Energy from electron–positron annihilation
An electron (mₑ = 9.11 × 10⁻³¹ kg) meets a positron and they annihilate. Find the total energy released (c = 3 × 10⁸ m/s).
E = 2mₑc² = 2 × 9.11×10⁻³¹ × (3×10⁸)² = 2 × 8.2×10⁻¹⁴ = 1.64 × 10⁻¹³ J (≈ 1.02 MeV)
Radius of a charged track in a magnetic field
A particle of charge e = 1.6 × 10⁻¹⁹ C and momentum p = 3.2 × 10⁻²⁰ kg·m/s moves perpendicular to a field B = 0.5 T. Find the track radius (r = p/qB).
r = p/(qB) = 3.2×10⁻²⁰ / (1.6×10⁻¹⁹ × 0.5) = 3.2×10⁻²⁰ / 8×10⁻²⁰ = 0.40 m
Rest energy of a proton
Find the rest energy of a proton (mₚ = 1.67 × 10⁻²⁷ kg) in joules and MeV.
E = mₚc² = 1.67×10⁻²⁷ × (3×10⁸)² = 1.50 × 10⁻¹⁰ J
In MeV: 1.50×10⁻¹⁰ / 1.6×10⁻¹³ = ≈ 938 MeV
Checking a conservation law in a decay
In β⁻ decay a neutron changes into a proton plus an electron and an antineutrino: n → p + e⁻ + ν̄ₑ. Check charge conservation.
Before: charge of n = 0. After: (+1) + (−1) + 0 = 0 — charge is conserved