CBSE Class 11-science Answered

There are atomic clocks which are the most accurate clocks ever made. The clock uses an electronic transition frequency in a region of the electromagnetic spectrum of atoms as a frequency standard to keep accurate time. The atomic clock is so accurate that it will neither gain nor lose a second in more than 138 million years.

The various types of atomic clocks include:

• Cesium atomic clocks employ a beam of cesium atoms. The clock separates cesium atoms of different energy levels by magnetic field.
• Hydrogen atomic clocks maintain hydrogen atoms at the required energy level in a container with walls of a special material so that the atoms don't lose their higher energy state too quickly.
• Rubidium atomic clocks, the simplest and most compact of all, use a glass cell of rubidium gas that changes its absorption of light at the optical rubidium frequency when the surrounding microwave frequency is just right.