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  2. Atomic clock - Wikipedia

    en.wikipedia.org/wiki/Atomic_clock

    The second, symbol s, is the SI unit of time. It is defined by taking the fixed numerical value of the caesium frequency, , the unperturbed ground-state hyperfine transition frequency of the caesium-133 atom, to be 9 192 631 770 when expressed in the unit Hz, which is equal to s −1.

  3. Half-life - Wikipedia

    en.wikipedia.org/wiki/Half-life

    For example, if there is just one radioactive atom, and its half-life is one second, there will not be "half of an atom" left after one second. Instead, the half-life is defined in terms of probability: "Half-life is the time required for exactly half of the entities to decay on average". In other words, the probability of a radioactive atom ...

  4. Atom - Wikipedia

    en.wikipedia.org/wiki/Atom

    The number of protons in an atom (which Rutherford called the "atomic number" [27] [28]) was found to be equal to the element's ordinal number on the periodic table and therefore provided a simple and clear-cut way of distinguishing the elements from each other. The atomic weight of each element is higher than its proton number, so Rutherford ...

  5. Atom (time) - Wikipedia

    en.wikipedia.org/wiki/Atom_(time)

    One of the earliest occurrences of the word "atom" to mean the smallest possible unit of measuring time is found in the Greek text of the New Testament in Paul's 1 Corinthians 15:52. The text compares the length of time of the “atom” to the time needed for "the twinkling of an eye."

  6. Term symbol - Wikipedia

    en.wikipedia.org/wiki/Term_symbol

    S is the total spin quantum number for the atom's electrons. The value 2S + 1 written in the term symbol is the spin multiplicity, which is the number of possible values of the spin magnetic quantum number M S for a given spin S. J is the total angular momentum quantum number for the atom's electrons. J has a value in the range from |L − S ...

  7. Nickel - Wikipedia

    en.wikipedia.org/wiki/Nickel

    The US nickel coin contains 0.04 ounces (1.1 g) of nickel, which at the April 2007 price was worth 6.5 cents, along with 3.75 grams of copper worth about 3 cents, with a total metal value of more than 9 cents. Since the face value of a nickel is 5 cents, this made it an attractive target for melting by people wanting to sell the metals at a profit.

  8. Chemical element - Wikipedia

    en.wikipedia.org/wiki/Chemical_element

    A chemical element is a chemical substance whose atoms all have the same number of protons.The number of protons is called the atomic number of that element. For example, oxygen has an atomic number of 8, meaning each oxygen atom has 8 protons in its nucleus.

  9. Half time (physics) - Wikipedia

    en.wikipedia.org/wiki/Half_time_(physics)

    The voltage (v) on the capacitor (C) changes with time as the capacitor is charged or discharged via the resistor (R) In electronics, when a capacitor is charged or discharged via a resistor, the voltage on the capacitor follows the above formula, with the half time approximately equal to 0.69 times the time constant, which is equal to the product of the resistance and the capacitance.