An electron enters a magnetic field parallel to the field lines. Force is MCQ with Answer and Explanation

Explanation:
Newton's law: F = Gm₁m₂/r² ⇒ F ∝ 1/r². Inverse square law fundamental to gravitation, electrostatics, and radiation intensity. Memory aid: 'Gravity weakens with square of distance; double distance ⇒ force becomes 1/4'. Core concept frequently tested to verify understanding of fundamental force laws in competitive exams.

Explanation:
Volume V = (4/3)πr³, so ΔV/V = 3 Δr/r. Percentage error in volume = 3 × 2% = 6%.

Explanation:
sin C = 1/μ = 2/3 ≈ 0.6667, C = sin⁻¹(2/3). So option A: sin⁻¹(2/3). Wait sin C = n2/n1 = 1/1.5 = 2/3. So C = sin⁻¹(2/3). Option A is sin⁻¹(2/3). I'll correct to A.