Class 12 Atoms CBSE Questions & Answers

Class 12 · Atoms

This is Physics Class 12 Atoms CBSE Questions & Answers. There are 15 questions in this test with each question having around four answer choices.

Questions & Answers

1
Emission line spectra of different elements
  • A
    is the same if both elements are in liquid form
  • B
    is different
    Correct
  • C
    is not different
  • D
    is the same if both elements are at the same temperature
2
Which of these statements about Bohr model is correct?
  • A
    Bohr model postulates wavy paths around the nucleus
  • B
    Bohr model combines classical and early quantum concepts
    Correct
  • C
    Bohr model is based classical electromagnetic theory
  • D
    Bohr model is pure quantum mechanical theory
3
Which of these statements about Bohr model hypothesis is correct?
  • A
    angular momentum of electron is quantized
    Correct
  • B
    mass of electron is quantized
  • C
    radius of electron is quantized
  • D
    velocity of electron is quantized
4
Which of these statements about De Broglie Explanation of Bohr model is correct?
  • A
    electron in its circular orbit, as proposed by Bohr, must be seen as electromagnetic wave
  • B
    electron in its circular orbit, as proposed by Bohr, must be seen as a particle .
  • C
    travelling wave is formed on a circular orbit where integral number of de Broglie Wavelengths fit into the circumference of the orbit \( < {\rm{p}} > \)
  • D
    Standing wave is formed on a circular orbit where integral number of de Broglie wavelengths fit into the circumference of the orbit
    Correct
5
Which of these statements about Bohr model applied to hydrogen atom correct?
  • A
    hydrogen atom in its ground level has no magnetic moment due to orbital motion
  • B
    hydrogen atom in quantized orbits radiates electromagnetic waves
  • C
    hydrogen atom in some orbits radiates electromagnetic waves
  • D
    hydrogen atom in its ground level has magnetic moment due to orbital motion
    Correct
6
Fluorescence is
  • A
    what happens in a fluorescent lamp
  • B
    it consists of a molecule, atom or nanostructure relaxing to its ground state by emitting a photon of light after being excited to a higher quantum state by some type of energy
    Correct
  • C
    it consists of accelerated atoms/molecules striking suitable material
  • D
    it consists only of atoms going into stable excited states
7
Reason why there are many lines in an atomic spectrum is because
  • A
    All atoms are in the same excited state and make transition to same state
  • B
    There are many atoms in different states of excitation making transition to the same state
  • C
    There are many atoms in different states of excitation making transition to different states
    Correct
  • D
    All atoms are in the same excited state and make transition to different states
8
Balmer series emission wavelengths are described by
  • A
    \({1 \over \lambda } = R\left( {{1 \over {{3^2}}} - {1 \over {{n^2}}}} \right)\)
  • B
    \({1 \over \lambda } = R\left( {{1 \over {{4^2}}} - {1 \over {{n^2}}}} \right)\)
  • C
    \({1 \over \lambda } = R\left( {{1 \over {{2^2}}} - {1 \over {3{n^2}}}} \right)\)
  • D
    \({1 \over {\lambda }} = R\left( {{1 \over {{2^2}}} - {1 \over {{n^2}}}} \right)\)
    Correct
9
Paschen series emission wavelengths are described by
  • A
    \({1 \over {\lambda }} = R\left( {{1 \over {{2^2}}} - {1 \over {{n^2}}}} \right)\)series
  • B
    \({1 \over \lambda } = R\left( {{1 \over {{2^2}}} - {1 \over {3{n^2}}}} \right)\)
  • C
    \({1 \over \lambda } = R\left( {{1 \over {{4^2}}} - {1 \over {{n^2}}}} \right)\)
  • D
    \({1 \over \lambda } = R\left( {{1 \over {{3^2}}} - {1 \over {{n^2}}}} \right)\)
    Correct
10
Fluorescent lamps are more efficient than incandescent lamps in converting electrical energy to visible light because
  • A
    they produce more white light
  • B
    they do not waste as much energy producing visible photons
  • C
    they do not waste as much energy producing (invisible) infrared photons
    Correct
  • D
    they do not use uv radiations
11
According to Bohr model radiation takes place when
  • A
    there is transition from one of the stable orbits of definite energy to another of higher energy
  • B
    there is transition from one of the stable orbits of definite energy to another of lower energy. hν = \({{\rm{E}}_{\rm{f}}} - {\rm{ }}{{\rm{E}}_{\rm{i}}}\)
    Correct
  • C
    there is transition from one of the unstable orbits of definite energy to another of higher energy
  • D
    there is transition from one of the unstable orbits of definite energy to another of same energy
12
According to Bohr model allowed values of angular momentum are
  • A
    integral multiples of h
  • B
    integral multiples of h/2 \(\pi \)
    Correct
  • C
    integral multiples of h/ \(\pi \)
  • D
    continuous
13
According to Bohr model speed of moving electron in the nth orbit is
  • A
    \({{{e^2}} \over {4\pi h{_0}}}\)
  • B
    \({{2{e^2}} \over {4\pi {_0}n}}\)
  • C
    \({{{e^2}} \over {2{_0}nh}}\)
    Correct
  • D
    \({{3{e^2}} \over {4\pi {_0}nh}}\)
14
According to Bohr model orbital radii are given by
  • A
    \({{{\varepsilon _0}{n^2}{m^2}} \over {\pi {e^2}}}\)
  • B
    \({{{\varepsilon _0}{n^2}{h^2}} \over {{e^2}}}\)
  • C
    \({{{n^2}{h^2}} \over {\pi m{e^2}}}\)
  • D
    \({{{\varepsilon _0}{n^2}{h^2}} \over {\pi m{e^2}}}\)
    Correct
15
In a Geiger -Marsden experiment, what is the distance of closest approach d to the nucleus of a 7.7 MeV \(\alpha - \)particle before it comes momentarily to rest and reverses its direction?
  • A
    35 fm
  • B
    30 fm
    Correct
  • C
    45 fm
  • D
    40 fm