The device used to increase or decrease AC voltage is MCQ with Answer and Explanation

Explanation:
Oil immersion increases numerical aperture (NA) by matching refractive indices, improving resolution d = λ/(2NA). Memory tip: 'Higher NA or shorter λ ⇒ better resolution'. Optical instrument concept frequently tested in competitive exams.

Explanation:
Recoil is due to action-reaction pair: gun exerts forward force on bullet, bullet exerts backward force on gun. Newton's third law states for every action there is equal and opposite reaction. Conservation of momentum also explains recoil, but the immediate law is third law. Gun recoil velocity is calculated using conservation of momentum derived from third law.

Explanation:
Three significant figures require the number to be written with three meaningful digits. 3.00 × 10⁸ m/s has three significant figures (3,0,0). 3 × 10⁸ has one significant figure; 3.0 × 10⁸ has two; 300000000 has ambiguous significance. Standard scientific notation: 3.00 × 10⁸ m/s. This is important in precision measurements.