Physics MCQs

Notes:
The ohm is the SI unit of electrical resistance. Electrical resistance of an object is the measure of its obstruction to the flow of electric current. It mainly depends on the material it is made of, cross sectional area of a conductor, length and temperature. The resistance of a conductor of unit cross-sectional area and unit length is known as Resistivity. The unit of resistivity is ohm-metre.

Notes:
Sublimation is the process by which a substance transitions from a solid to a gas without passing through a liquid phase. This typically occurs when a substance is heated to a temperature at which its solid form becomes a gas, such as when dry ice (solid carbon dioxide) sublimates and turns into gas. Sublimation can also occur when a substance is exposed to a vacuum, which can cause gases to be drawn out of the substance and turn into a solid. Sublimation is an important process in many scientific and industrial fields, including meteorology, chemistry, and materials science. Camphor is also an example of Sublimation.

Notes:
The correct answer is that the person hears the sound waves twice: first via steel and then via air. Sound travels faster in solids than in gases. in steel, it travels at about 5,960 m/s, while in air, it travels at approximately 343 m/s. Given the long distance of 700 meters, the sound will reach the person through the steel rail first, followed by the sound traveling through the air. This phenomenon illustrates the differences in sound propagation speeds in different media.

Notes:
Albert Einstein was awarded the Nobel Prize in Physics in 1921 for his groundbreaking theoretical work on the nature of light and the fundamental relationship between energy and matter. Einstein’s most famous contribution to science was his theory of relativity, which was published in 1905 and expanded upon in later years. His theory showed that the laws of physics are the same for all non-accelerating observers, and that the speed of light in a vacuum is constant and independent of the motion of the observer. This revolutionary idea challenged many of the long-held beliefs about the nature of space, time, and the fundamental forces of the universe, and it has had a profound impact on the field of physics and our understanding of the universe.

Notes:
It is just a feeling, we are actually being pushed towards the moving train by the atmosphere surrounding us. The reason can be explained with the help of “Bernoulli’s law”. When a train is stationary, the pressure at points in surrounding area would be uniform and at atmospheric pressure. As the train starts and gains momentum, the increasing velocity of the train depletes the pressure at the points in the area at close proximity to the train. Now the pressure at these points is less than atmospheric pressure. The points at an area farther away from the train are at same atmospheric pressure as before. It has to be noted that, the velocity of the train affects pressure of the areas closer to the train and not of those a little far away. Naturally, air from the points at atmospheric pressure (relatively high) would rush towards the low pressure area (the area immediately surrounding the train) or towards the train. Thus a person standing near a moving train will actually be pushed towards the train by the gush of wind destined to the low pressure area.

Notes:
Normal clocks and watches work on either mechanical or electronic control systems. These systems are not very accurate as they can be affected by many factors. On the other hand, atomic clocks keep time by the oscillation of the nucleus of an atom and its surrounding electrons. The mass of the nucleus and the gravity and electrostatic “spring” between the positively charged nucleus and the electrons set the oscillation frequencies. This oscillation is not directly analogous to the time keeping of normal clocks, but both types of clocks use oscillations to keep track of time. Atomic clocks are more reliable time keepers because their oscillations are not subject to change according to environmental factors such as humidity that would decrease the accuracy of normal clocks. A common misconception is that the atomic clock works on radioactive disintegration of the nuclei. These clocks do not keep time according to atomic decay. In quartz clocks, the vibrations of a quartz crystal are controlled and used to measure time. The quartz vibrates at the rate of 32,768 Hz when electricity is passed through it.

Notes:
bar, torr and Pascal are the units used for measuring pressure whereas shake is a unit of time. 1 bar = 10⁵ Pa 1 bar = 760 torr 1 bar = 1 atmospheric pressure Shake is the smallest practical unit of time. 1 shake = 10^-8s

Notes:
The SI unit of Linear Momentum is kg m/s Linear Momentum = Mass(kg) x Velocity (m/s) Linear Momentum is the quantity of motion of a moving body. Dimensional Formula of Linear Momentum is [M¹ L¹ T^-1]

Notes:
When one body is actually moving over the surface of other body, the friction is known as Kinetic friction. It is also known as dynamic friction.

Notes:
The coefficient of static friction can be defined as the ratio of the limiting static friction and the normal reaction between the 2 surfaces. The value of coefficient of limiting friction depends: 1. Nature of the surfaces in contact. 2. Material of the surfaces in contact