A photon collides with a stationary hydrogen atom in the ground state inelastically. The energy of the colliding photon is 10.2 eV. After a time interval of the order of microseconds, another photon collides with the same hydrogen atom inelastically with an energy of 15 eV. What will be observed by the detector?
A photon collides with a stationary hydrogen atom in the ground state inelastically. The energy of the colliding photon is 10.2 eV. After a time interval of the order of microseconds, another photon collides with the same hydrogen atom inelastically with an energy of 15 eV. What will be observed by the detector?
Show Hint
The first photon will excite the hydrogen atom (in the ground state) to the first excited state.
- 2 photons of energy 10.2 eV
- 2 photons of energy 1.4 eV
- One photon of energy 10.2 eV and an electron of energy 1.4 eV
- One photon of energy 10.2 eV and another photon of energy 1.4 eV
The Correct Option is C
Solution and Explanation
The first photon will excite the hydrogen atom (in ground state) to first excited state (as $E_2-E_1 = 10.2eV).$
- Hence, during de-excitation, due to the 10.2 eV photon, one photon of energy of 10.2 eV will be detected.
- The second photon of energy 15 eV can ionize the atom.
- The balance energy i.e. (15- 13,6)eV = 1.4 eV is retained by the electron.
- Therefore, by the second photon, an electron of 1.4 eV energy will be released.
$\therefore$ the correct answer is (c).
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Concepts Used:
Atoms
- The smallest unit of matter indivisible by chemical means is known as an atom.
- The fundamental building block of a chemical element.
- The smallest possible unit of an element that still has all the chemical properties of that element.
- An atom is consisting of a nucleus surrounded by one or more shells of electrons.
- Word origin: from the Greek word atomos, which means uncuttable, something that cannot be divided further.
All matter we encounter in everyday life consists of smallest units called atoms – the air we breath consists of a wildly careening crowd of little groups of atoms, my computer’s keyboard of a tangle of atom chains, the metal surface it rests on is a crystal lattice of atoms. All the variety of matter consists of less than hundred species of atoms (in other words: less than a hundred different chemical elements).
Every atom consists of an nucleus surrounded by a cloud of electrons. Nearly all of the atom’s mass is concentrated in its nucleus, while the structure of the electron cloud determines how the atom can bind to other atoms (in other words: its chemical properties). Every chemical element can be defined via a characteristic number of protons in its nucleus. Atoms that have lost some of their usual number of electrons are called ions. Atoms are extremely small (typical diameters are in the region of tenths of a billionth of a metre = 10-10 metres), and to describe their properties and behaviour, one has to resort to quantum theory.