[Physics Class Notes] on Second Pdf for Exam

Second Definition

Do you know what is a second? This is a measuring unit of time that helps us to detect the accurate period.

People sometimes get confused with the question ‘what is a second?’. Each clock has a tiny and thin stick that revolves around the entire number (starts from and ends at 12).

What to answer to this question, ‘how is a second defined’? The answer is very simple and helpful. You will know the process of acknowledging the time from the clock. This information here is going to help you to know more regarding the second definition.

How is a Second Measured?

It is officially confirmed that 1 second can be measured by the time consumption of 9,192,631,770 cycles of radiations of electrons. The observation is quite simple as the electrons that radiate energy are two different energy levels of the atom called caesium-133.

History of the Second?

The second was used initially as a minimum calculation of time. But the evolution of time makes certain corrections to this concept. As of now, second is one of the fundamental units of time. You can find second definition Physics in terms of the radiation frequency.

From previous concepts, second was used to define 1/86,400 of the mean solar day. This helps you to understand the concept that the value for a second is the average period of rotation of the earth on its axis. The axis of movement (rotational motion) of the earth is relative to the sun.

[]

Definition of Seconds in Time

During the 20th century, the old definition of time became inadequate. The reason behind this is the requirement for augmented precision in timekeeping. 

Another definition came for second in 1957. It was put forward by the International Committee on Weights and Measures. The committee had decided that second was the 1/31,556,925.9747 of the length of the tropical year (1900). 

But that’s not the end. However, In the middle of 1967, the 13th General Conference on Weights and Measures had decided conditionally to define the second as 9,192,631,770 cycles of radiation.

The revolution was linked with the alteration between the two hyperfine levels. Each level of a caesium-133 atom was coming active from its ground state.

[].

The scientists had chosen the number of cycles of radiation for measuring the length of the defined second. Each radiation from the Cs atom was taken as closely as possible. 

Nowadays, it is an obsolete method that was developed astronomically to determine the second of Ephemeris Time.  The statement had the definition over the fraction of the tropical year given above. 

Some constant observations tell us that the revolution period of the Earth constantly changes. So, all of those theories won’t stand firm after it is recognized that the earth’s revolution is not constant. 

Some mandatory processes need to be added occasionally for defining the ‘second’. The definition of the second ensures that the atomic timescale remains in synchronization with nature. 

We call it Coordinated Universal Time (UTC). UTC is the one who represents the sole definition of the second in the International System of Units (SI).

What is Second in Physics? 

Second is the important segment of time. In modern time-format, second has the ultimate role. Some conversions of second are given in a table below:

Time (including hour, minute, and second) is one of the important segments of our lives. We are dealing with almost everything by doing some sort of things such as keeping time, following time, and telling time. Times is the unchangeable fact that influences every aspect of our lives, either indirectly or directly. 

What Comes Before Seconds?

Students should understand the concept of what does appear before the seconds. Well, they are some measures of time that stand lesser than the second. The list is given below that defines some of the smallest units of the second:

1. Pico-second = One-trillionth of a second

2. Femto-second = One-quadrillionth of a second

3. Deci-second = One-tenth of a second

4. Centi-second = One-hundredth of a second

5. Micro-second = One-millionth of a second

6. Nano-second = One-billionth of a second

7. Milli-second = One-thousandth of a second

8. Atto-second = One-quintillionth of a second

9. Zepto-second = One-sextillionth of a second

10. Yoctosecond = One-septillionth of a second

11. Planck time = Shortest measurable time (based on theory)

Our society spectates the time as a bridge of separation that comes in between the present and past tense. However, time plays a significant role in physics as it is used to measure motion and forces.

One of the greatest discoveries known is Einstein’s theory of relativity. This theory also declares the concept of decelerating time with the object’s motion and earth’s gravity.