Metrology is the comparison of physical quantity with its equivalent quantity. Measurement is the basis of all scientific research and experiments. Physics is a quantitative science. Physicists always deal with numbers that represent physical measurements. It is the foundation for all technological development.
The accuracy of measurement is more important in science. But sometimes we fail to calculate the exact value in the measurement. It's quite hard to find the exact value of any measurement. In such cases, it will cause an error. So there is no possibility to find accurate measurements. For example, when we buy any fruits or vegetables, vendors measure the unknown weight of the fruits or vegetables with the known weight with the help of a weight scale.
Physical quantities consist of a numerical value ( a number ) and a unit of measurement. Example: 3 kilograms. Suppose you buy 3kg of vegetables from a shop. Where 3 is the numerical value and kilogram is the unit. A unit is a measurable quantity to which the unknown quantity can be compared.
A unit is defined as a physical quantity having a definite numerical value accepted by rules or conventions. For example, a foot is a unit of length. 10 feet means 10 times the finite length of 1 foot. In earlier times, different unit systems were used by different nations. But at the end of World War two, there was a need for a global unit system.
The units used to measure basic quantities are called fundamental units and are units obtained by appropriate multiplication or division of the fundamental units to measure other physical quantities also called derived units. The SI unit system is a modernized and improved unit system over the ancient unit systems. This method has been adopted by almost all the countries of the world. It consists of some basic units. Other ways can be derived from those basic units by proper connection.
Time is the measure of events and the intervals between them. Galileo’s invention of the simple pendulum in 1602 was the most reliable instrument for measuring time. At that time, it was customary to hand chandeliers from the ceilings. He then observed a chandelier suspended from the ceiling of a church swaying back and forth in the wind and devised a unique pendulum, an instrument for measuring time.
One swing of the pendulum is a full motion of the pendulum ball swinging as the pendulum swings back and forth from its centre point. The maximum displacement of the pendulum in any direction from the centre point is called the amplitude of oscillation of the pendulum.
SI unit of time is Second. The time required for light to travel a distance of 29,97,924 meters in a vacuum is one second. A second is also given as 1/86,400 times a mean solar day.
In our daily life, we are using various units of time for different actions. For example, the time take to travel by a vehicle is calculated in hour, we can calculate time taken to press a switch in seconds etc. The large units of time are the day, month, year and millennium.
$$\mathrm{1\:millennium = 3.16\times 10^9\: second}$$
$$\mathrm{1\:minute =60\:seconds}$$
$$\mathrm{1\:hour = 60\:minutes\:or\:3600 \:seconds}$$
$$\mathrm{1\:day=24\:hour\:or\:86400\: seconds}$$
$$\mathrm{1\:year=365.25\:day}$$
Time intervals are measured by the clock. The atomic periodic table is based on the uniform vibrations produced by the caesium atom. Electric oscillators, electronic oscillators, solar cell clocks, the decay time of elementary particles, and radiological age predictions are some of the clocks developed at present.
The handle on the sundial is set so that the object casts a shadow on a horizontal surface. As the sun changes in the sky, the shadow cast on the sundial changes. Time is calculated by this change. Later sundials were designed to be more accurate so that the smallest measurement that this sundial could measure was 1 hour, which was as small as 15 minutes.
Water is kept dripping at a specified rate into a graduated beaker equipped 
with a float and a needle system. As the water drips into the beaker, the water level in the beaker rises. The period can be known from the measurements marked on the side wall of the vessel. The rate at which water drips depends on the level of water in the overhead tank. The overhead tank is set up and the drip rate is constant. Although there is a change in the time measured by this clock, these clocks are very popular among people due to their accuracy of one-quarter of an hour.
It is made up of two circular glass bulbs. The glass bubbles are connected by a very narrow opening. When the hourglass is turned upside down, the fine sand from the top glass bubble enters the bottom glass bubble through the opening in the middle. The clock is also known as the hour clock because it takes one hour for the sand to reach the bottom.
Time is the measure of events and the intervals between them. Time intervals are measured by the clock. We use varies types of clocks Sundial, Water clock, Sand clock like and mechanically and battery-operated clocks to measure time.
Electric oscillators, electronic oscillators, solar cell clocks, the decay time of elementary particles, and radiological age predictions are some of the clocks developed at present. The atomic periodic table is based on the uniform vibrations produced by the caesium atom.
Q1. What are atomic clocks?
Ans. These clocks work on the basis of regular vibrations in the caesium atom. Atomic clocks are currently used as the most accurate clocks.
Q2. Define the accuracy of time measuring instruments
Ans. If one clock goes behind at the rate of 5 minutes per month and the other at the rate of 5 minutes per month, then the 2nd clock is considered to be more accurate. Because the time shown by the second clock is closest to the correct time.
Q3. What is unit conversion?
Ans. Unit conversion refers to the process of changing a unit of a physical quantity from one unit to another unit. To simplify the calculations, unit conversion is necessary to express the results necessarily.
Q4. Define Mass
Ans. The amount of matter present in an object is called mass. A kilogram is the SI unit of mass. A kilogram is the mass of a prototype cylinder made of platinum-iridium alloy kept at the International
Q5. What is Screw Gauge?
Ans. A screw gauge is a measuring instrument accurate to one-hundredth of a millimetre (0.01mm). This instrument can measure the diameter of thin wire, the thickness of thin metal plate, etc.
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