Physics MCQs

Notes:
Actually a black board has all colours in light or white light . So when light falls on it board absorbs all colours because all are present so no light is reflected back . That is the case when board has all colours and so it will appear black as it absorbs all colours of light that fall on it .

Notes:
Mass is the amount of matter enclosed by a body so it can never change with displacement in a body. Weight is a force actually force due to gravity taking earth into consideration. Therefore outside earth this force is negligible. Hence weight is zero. As W=mg, where g is the force due to gravity. When ‘g’ is almost negligible or nil, weight becomes zero. Hence outside earth weight is zero while mass is constant.

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:
Radio waves travel very quickly through space. Radio waves are a kind of electromagnetic radiation, and thus they move at the speed of light. The speed of light is a little less than 300,000 km per second. At that speed, a beam of light could go around the Earth at the equator more than 7 times in a second.

Notes:
Normal body temperature of human is 37° C. But when we convert 37° C into Kelvin it becomes 310 K because 0° C = 0°C + 273 = 273 K.

Notes:
When light enters from rarer (air) to denser (glass) medium wavelength and velocity will get affected. The velocity will decrease. Moreover, as the ray bent in passing through different media which results in decrease of wavelength. As such there is no change in frequency when light enters from air to glass.

Notes:
Sound is a longitudinal wave. Longitudinal wave is a wave where the direction of propagation of the wave and movement of particles is in the same direction where as in transverse wave they are perpendicular to each other. 
Extra info: Example of transverse wave is light wave (electromagnetic wave).

Notes:
The energy possessed by a body by virtue of its motion is called kinetic energy. Potential Energy is the energy possessed by virtue of its position or configuration. When a body falls from an aeroplane, there is increase in its acceleration as it fall under the influence of force of gravity.

Notes:
Since Torque = force x distance, to open a door easily, the handle should be fixed at the greatest distance from the hinges. If we pull with same force on a handle that is 2 feet away from the hinges, we will provide twice the torque, so it will be twice as easy to open.

Notes:
Water at ordinary temperatures contracts and increases in density as it is cooled, like most substances. But at 4°C, it reaches its maximum density and then decreases in density as it approaches the freezing point. This is referred to as anomalous property of water according to which density reduced with the decreasing temperature.