Given below are two statements: 
Assertion (A): The absorption line observed in the spectra of an element is never completely dark.
Reason (R): The sample used for absorption is thin, so that all photons corresponding to a transition may not be absorbed.
  
1. Both (A) and (R) are true and (R) is the correct explanation of (A).
2. Both (A) and (R) are true but (R) is not the correct explanation of (A).
3. (A) is true but (R) is false.
4. Both (A) and (R) are false.



 
Subtopic:  Spectral Series |
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Electrons accelerated through a potential difference \(V_0\) are incident on a gas of hydrogen atoms in the ground state. For what minimum value of \(V_0\) will the collisions of the electrons with the atom be perfectly inelastic?
1. \(13.6\) V
2. \(27.2\) V
3. \(10.2\) V
4. \(6.8\) V
Subtopic:  Bohr's Model of Atom |
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Among the given options which is the minimum work function so that light from the Balmer series will not be able to cause any photo-electric effect? 
1. \(13.6~\text{eV}\)
2. \(\dfrac{13.6} {2}~\text{eV}\)
3. \(13.6×\left(\dfrac{3}{4}\right)~\text{eV}\)
4. \(13.6×\left(\dfrac14-\dfrac19\right)~\text{eV}\)
Subtopic:  Spectral Series |
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A hydrogen atom collides with another similar atom at rest. The minimum energy of the first atom so that one of them may get ionised is:
1. \(13.6\) eV  2. \(\dfrac{13.6} {2}\) eV
3. \(2 \times 13.6\) eV 4. \(10.2\) eV 
Subtopic:  Bohr's Model of Atom |
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A hydrogen atom in the ground state absorbs an ultraviolet photon of wavelength \(25\) nm. Ignore any momentum associated with the photon. The ejected electron has an energy of nearly:
(Take \(hc = 1240\) eV-nm)
1. \(10\) eV 
2. \(25\) eV
3. \(35\) eV
4. \(50\) eV
Subtopic:  Bohr's Model of Atom |
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For the ground state, the electron in the H-atom has an angular momentum \(\dfrac h{2\pi}\), according to the simple Bohr model. Angular momentum is a vector and hence there will be infinitely many orbits with the vector pointing in all possible directions. In actuality, this is not true,

1. because the Bohr model gives incorrect values of angular momentum.
2. because only one of these would have a minimum energy.
3. angular momentum must be in the direction of the spin of the electron.
4. because electrons go around only in horizontal orbits.

Subtopic:  Bohr's Model of Atom |
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The simple Bohr model cannot be directly applied to calculate the energy levels of an atom with many electrons. This is because:

1. of the electrons not being subjected to a central force.
2. of the electrons colliding with each other.
3. of screening effects.
4. the force between the nucleus and an electron will no longer be given by Coulomb's law.
Subtopic:  Bohr's Model of Atom |
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The zero of the potential energy is so chosen that the total energy of the hydrogen atom in its \(1^{st}\) excited state is zero. Then, the energy of the ground state of the hydrogen atom is:
1. \(-3.4~\text{eV}\) 2. \(-6.8~\text{eV}\)
3. \(-10.2~\text{eV}\) 4. \(-13.6~\text{eV}\)
Subtopic:  Bohr's Model of Atom |
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The energy of an atom with a \(K\text-\)shell vacancy is \(E_K\), that with an \(L\text-\)shell vacancy is \(E_L\), and that with an \(M\text-\)shell vacancy is \(E_M\): all compared to an atom with no vacancy, then:
(I) \(E_K<E_L\)
(II) \(E_L>E_M\)
(III)  \(E_L -E_K=E_{K\alpha}\), the energy of \(K_\alpha \) photon
Choose the correct option from the options given below:
1. (I) is true 2. (I), (III) are true
3. (II) is true 4. (I), (II) are true
Subtopic:  Bohr's Model of Atom |
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The electrostatic potential at the location of an electron in the ground state of the \(\mathrm{H}\)-atom is:
1. \(13.6~\text V\)
2. \(6.8~\text V\) 
3. \(27.2~\text V\) 
4. \(3.4~\text V\) 
Subtopic:  Bohr's Model of Atom |
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