Which one of the following elements is used as a timekeeper in atomic clocks?

A Potassium
B Caesium
C Calcium
D Magnesium

Correct Answer: Caesium

When exposed to certain frequencies of radiation, such as radio waves, the subatomic particles called electrons that orbit an atom's nucleus will "jump" back and forth between energy states. Clocks based on this jumping within atoms can therefore provide an extremely precise way to count seconds.It is no surprise then that the international standard for the length of one second is based on atoms. Since 1967, the official definition of a second is 9,192,631,770 cycles of the radiation that gets an atom of the element called caesium to vibrate between two energy states.

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Related Questions

A man purchases two clocks A and B at a total cost of Tk 650. He sells A with a 20% profit and B at a loss of 25% and gets the same selling price for both clocks. What are the purchasing prices of A and B respectively? 
A 225, 425
B 275, 375
C 300, 350
D 250, 400
অ্যালুমিনিয়াম, হিলিয়াম এবং সিলিকনের পারমাণবিক সংখ্যা যথাক্রমে 13, 2 এবং 14 হলে, Al27+He27→Si27+( ) নিউক্লিয়ার বিক্রিয়াতে অনুপস্থিত কণা কোনটি? (Aluminum has atomic number 13, helium has atomic number 2, and silicon has atomic number 14. In the nuclear reaction the missing particle Al27+He27→Si27+( ) is:)
A A. an α particle
B a positron
C an electron
D a proton
. অ্যালুমিনিয়াম, হিলিয়াম এবং সিলিকনের পারমাণবিক সংখ্যা যথাক্রমে 13, 2 এবং 14 হলে, Al27+He27→Si27+ নিউক্লিয়ার বিক্রিয়াতে অনুপস্থিত কণা কোনটি ? (Aluminum has atomic number 13, helium has atomic number 2, and silicon has atomic number 14. In the nuclear reaction Al27+He27→Si27+ the missing particle is:)
A an a particle
B a positrom
C an electron
D a proton
Referring to the periodic table of elements, it is found that with increasing atomic number. The atomic size in the same
A Period increases
B Period decreases
C Group increases
D Both 'B' & 'C'
The transuranium elements are the chemical elements with atomic numbers greater than
A 86
B 89
C 92
D 96
Which of the following motors will be used in electric clocks ?
A D.C. shunt motor
B D.C. series motor
C A.induction motor
D A.C. synchronous motor
The material widely used for making pendulums of clocks is
A Stainless steel
B High speed steel
C Heat resisting steel
D Nickel steel
The gear train usually employed in clocks is a
A reverted gear train
B simple gear train
C sun and planet gear
D differential gear
If A has 4 elements and B has 8 elements then the minimum and maximum number of elements in A∪B are respectively __
A 4,8
B 8,12
C 4,12
D 6,12
The atomic weight and atomic number of an element are A and Z respectively. What is the number of neutrons in the atom of that element?
A Z
B A
C A+Z
D A-Z

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