Ground state and excited state

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Excited States and Ground States

ground state and excited state

The ground state in quantum mechanics is the minimal energy of an atom or molecule. An excited state is any state of energy higher than the ground state which.

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Atoms may occupy different energy states. The energy states are discrete, i. Therefore an atom can only move to a new energy level if it absorbs or emits an amount of energy that exactly corresponds to the difference between two energy levels. The lowest possible energy level that the atom can occupy is called the ground state. This is the energy state that would be considered normal for the atom.

In quantum mechanics , an excited state of a system such as an atom , molecule or nucleus is any quantum state of the system that has a higher energy than the ground state that is, more energy than the absolute minimum. Excitation is an elevation in energy level above an arbitrary baseline energy state. In physics there is a specific technical definition for energy level which is often associated with an atom being raised to an excited state. The lifetime of a system in an excited state is usually short: spontaneous or induced emission of a quantum of energy such as a photon or a phonon usually occurs shortly after the system is promoted to the excited state, returning the system to a state with lower energy a less excited state or the ground state. This return to a lower energy level is often loosely described as decay and is the inverse of excitation. Long-lived excited states are often called metastable.

A sustained laser beam can be achieved by using atoms that have two relatively stable levels between their ground state and a higher-energy excited state. As in a three-level laser, the atoms first drop to a long-lived metastable state where they can be stimulated to emit excess energy. However, instead of dropping to the ground state, they stop at another state above the ground state from which they can more easily be excited back up to the higher metastable state, thereby maintaining the population inversion needed for continuous laser operation. A burst of energy excites electrons in more than half of the atoms from their ground state to a higher state, creating a population inversion. The electrons then drop into a long-lived state with slightly less energy, where they can be stimulated to quickly shed excess energy as a laser burst, returning the electrons to a stable ground state. Thus, by measuring the energy of the radiation that has been absorbed by the atom, the difference inů.

The ground state of a quantum-mechanical system is its lowest- energy state ; the energy of the ground state is known as the zero-point energy of the system. An excited state is any state with energy greater than the ground state. In the quantum field theory , the ground state is usually called the vacuum state or the vacuum. If more than one ground state exists, they are said to be degenerate. Many systems have degenerate ground states. Degeneracy occurs whenever there exists a unitary operator that acts non-trivially on a ground state and commutes with the Hamiltonian of the system. According to the third law of thermodynamics , a system at absolute zero temperature exists in its ground state; thus, its entropy is determined by the degeneracy of the ground state.

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Ground state

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Excited state

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Ground State Vs. Excited State of an Atom: A Definitive Analysis

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5 thoughts on “Ground state and excited state

  1. Atoms are composed of an atomic nucleus and electrons that are in the movement around that nucleus.

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