A 5 Ω resistor dissipates 20 W power. Current through it is MCQ with Answer and Explanation

Explanation:
P = 1/f(m) ⇒ f = 1/P = 1/(-4) = -0.25 m = -25 cm. Negative focal length indicates diverging (concave) lens. Memory aid: 'Negative power = concave lens; f(cm) = 100/P(D)'. Direct lens power application frequently tested in competitive exams with sign convention awareness.

Explanation:
Speed of light ≈ 3×10⁸ m/s, sound ≈ 340 m/s. Light reaches almost instantly, sound takes time. So thunder heard after lightning. Time delay gives distance: d = v_sound × t.

Explanation:
Candela (cd) is SI base unit for luminous intensity. Lumen: luminous flux; Lux: illuminance; Watt: power. Memory aid: 'Candela = candle power; base unit for perceived light'. Unit knowledge frequently tested in competitive exams.