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)
Coulomb's law — force between two charges
Two point charges of +4 μC and +6 μC are placed 0.20 m apart in air. Find the force between them.
F = k·q₁q₂ / r² = (9×10⁹ × 4×10⁻⁶ × 6×10⁻⁶) / (0.20)²
F = (9×10⁹ × 24×10⁻¹²) / 0.04 = 0.216 / 0.04 = 5.4 N (repulsive)
Effect of distance (inverse-square)
The force between two charges is 8 N when they are 0.30 m apart. What is the force when the distance is reduced to 0.10 m (charges unchanged)?
F ∝ 1/r², so F₂/F₁ = (r₁/r₂)² = (0.30/0.10)² = 9
F₂ = 9 × 8 = 72 N
Electric field of a point charge
Find the electric field 0.50 m from a point charge of +2 μC in air.
E = k·Q / r² = (9×10⁹ × 2×10⁻⁶) / (0.50)²
E = 18000 / 0.25 = 7.2 × 10⁴ N/C (directed away from the charge)
Force from a field on a charge
A charge of 5 μC is placed in a uniform field of 3 × 10⁴ N/C. Find the force on it.
F = qE = 5×10⁻⁶ × 3×10⁴
F = 0.15 N
Electric potential of a point charge
Find the potential 0.30 m from a +5 μC charge in air.
V = k·Q / r = (9×10⁹ × 5×10⁻⁶) / 0.30
V = 45000 / 0.30 = 1.5 × 10⁵ V
Work done moving a charge through a p.d.
How much work is done in moving a charge of 2 μC through a potential difference of 5000 V?
W = qV = 2×10⁻⁶ × 5000
W = 0.01 J (10 mJ)