Physics MCQs

Notes:
During winter ice is formed only on the top layer of a pond or a lake because the water’s surface is usually slightly cooler than the rest of the body of water due to evaporative cooling. As water cools below 4 C, it also becomes slightly less dense, rising to the surface. Ice is also slightly less dense than the slightly warmer water below, so it floats on the water’s surface. Once ice crystals begin to form, they provide nucleation sites for additional ice to grow along the water’s surface. The islands of ice expand, until they cover the entire surface of the water.

Notes:
In 1922, Neils Henrik David Bohr won Nobel Prize in Physics for his remarkable contributions towards the understanding of the atomic structure and quantum theory. Neils Bohr was a Danish physicist born and died in Copenhagen, Denmark. He developed Bohr Model of the Atom, in which he proposed that energy levels of electrons are discrete and that the electrons revolve in stable orbits around the atomic nucleus but can jump from one energy level to another.

Notes:
A seconds pendulum is a pendulum whose period is precisely two seconds; one second for a swing in one direction and other second for the return swing, it has a frequency of 1/2 Hz. At standard gravity, its length is 0.994 m.

Notes:
The SI unit of work is the Newton-metre or joule (J). A Newton metre is also the SI unit of torque (also called moment or moment of force).

Notes:
In the reference frame of the platform the ball has initial horizontal velocity equal to the velocity of the train. The vertical direction is the same observed on the train because both observers agree that gravity is acting on the ball causing an acceleration g. But, in the platform’s reference frame it already had x-velocity, and the resultant path would be a parabola.

Notes:
A parsec is a unit of length used to measure large distances between objects outside our Solar System. One parsec is the distance equal to about 3.26 lightyears in length.

Notes:
According to Newton’s third law of motion, to every action there is an equal and opposite reaction’. It indicates that when one object exerts a force on another object, the second object instantaneously exerts a force back on the first object. These two forces are always equal in magnitude, but opposite in direction.

Notes:
According to Archimedes Principle, the weight of the water displaced by the hull of a floating boat equals the total weight of the boat and its contents. If iron nails are removed from the boat, it becomes lighter and displaces less water. That means the boat rises up so that less of its volume is below the surface, while the water level falls because it now displaces less water when submerged.

Notes:
According to Archimedes Principle and law of floatation the buoyant force acting an an object/body immersed in a liquid is affected by its density with the increasing liquid’s density, byoyant force acted upon increases too. The sea water beings saline is more denser than river water hence, applies more buoyant force making a swimmer to swim easily with less efforts.

Notes:
Real gases approximate ideal gases when their pressure is relatively low, and their temperature is reasonably high. A real gas deviates increasingly from ideality as it is compressed and cooled to near the point at which it will condense into a liquid. Compressing forces the molecules closer together so that intermolecular forces become stronger, and cooling reduces the kinetic energy of the molecules, so that they are more easily held by these forces.