What Exactly is One Second? | History of Second | Hello Science | Vikrant Kirar

NCERT Physics Class 11 Chapter 2 Units and Measurement, measurement of time. Everyone has once in their life thought of time-travel. But has anyone wondered how do we exactly measure time? Can we really know how long is a second? How can one tell the exact number of cycles of radiation a cesium-133 atom makes in order to define one second? Vikrant Kirar is back to satisfy the curiosity and answer all these questions and much more. Vikrant travels back in time and takes us through the history of a second. The second is the base unit of time in the International System of Units (SI), commonly understood and historically defined as ​1⁄86400 of a day – this factor derived from the division of the day first into 24 hours, then to 60 minutes and finally to 60 seconds each. Although the historical definition of the unit was based on this division of the Earth's rotation cycle, the formal definition in the International System of Units (SI) is a much steadier timekeeper: it is defined by taking the fixed numerical value of the cesium frequency ∆νCs. The second is the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom. Vikrant Kirar and other top educators are teaching live on Unacademy. Use code “CRASHUP" or "VIKRANT” to get 10% off on your Unacademy Subscription. Vikrant Kirar's profile- https://unacademy.com/@crashup Crashup Channel Link:    / crashup   Join our Telegram channel: https://t.me/HelloSci Watch the full playlist here -    • Explore Science Definitions | Fun Science ...   Do Subscribe and be a part of the community for more such lessons here:    / @helloscience7438   Unacademy Subscription Benefits: 1. Learn from your favorite teacher 2. Dedicated DOUBT sessions 3. One Subscription, Unlimited Access 4. Real-time interaction with Teachers 5. You can ask doubts in a live class 6. Limited students 7. Download the videos & watch offline #helloScience #IITJEE #measurementofTime