The part of human eye that controls amount of light entering is MCQ with Answer and Explanation

Explanation:
Using the second equation of motion for free fall: h = ut + ½gt². Since it is dropped, initial velocity (u) = 0. Time (t) = 4s, g = 10 m/s². The height h = 0 + ½(10)(4)² = 5 × 16 = 80 meters.

Explanation:
In uniform circular motion, speed is constant but velocity direction changes continuously, producing centripetal acceleration. Magnitude a = v²/r, direction always towards the center of the circle. This acceleration changes velocity direction without altering speed. Tangential acceleration would change speed, but here speed is constant. Formula derivation: From vector analysis of velocity change over small time interval. Exam tip: Remember 'centripetal' means 'center-seeking'; this concept is fundamental for rotational dynamics questions in competitive exams.

Explanation:
Materials are classified by their magnetic properties. Ferromagnetic materials (Iron, Cobalt, Nickel) are strongly attracted to magnets. Paramagnetic materials (Aluminum, Platinum) are weakly attracted. Diamagnetic materials (Water, Bismuth, Copper, Gold) are actually weakly repelled by a magnetic field because they create an induced magnetic field in opposition to the externally applied one.