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)
Number of neutrons in a nucleus
How many neutrons are there in a uranium-235 nucleus (Z = 92)?
N = A − Z = 235 − 92 = 143 neutrons
Energy released from a mass defect (E = mc²)
A nuclear reaction has a mass defect Δm = 0.02 u. Find the energy released (1 u = 931 MeV).
E = Δm × 931 MeV/u = 0.02 × 931 = 18.62 MeV
Binding energy and binding energy per nucleon
A ⁴He (alpha) nucleus has a mass defect of 0.0304 u (A = 4). Find its binding energy and B.E. per nucleon.
B.E. = 0.0304 × 931 = 28.3 MeV
B.E. per nucleon = 28.3 / 4 = 7.07 MeV/nucleon
Fraction of a sample left after several half-lives
A radioactive sample has a half-life of 8 days. What fraction remains after 24 days?
n = t/T½ = 24/8 = 3 half-lives
Fraction = (½)ⁿ = (½)³ = 1/8 (0.125, i.e. 12.5 %)
Mass remaining after a number of half-lives
An initial 80 g sample has a half-life of 5 years. How much remains after 15 years?
n = 15/5 = 3 ⇒ remaining = 80 × (½)³ = 80 × 1/8 = 10 g
Decay constant from the half-life
A radioactive nuclide has a half-life of 5.0 s. Find its decay constant λ.
λ = 0.693 / T½ = 0.693 / 5.0 = 0.139 s⁻¹