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Atoms Physics - Atoms

Uttarakhand Board (UBSE) - STD 12 Science - Physics (Uttarakhand - English Medium). 402 questions in this chapter.

Question types

Atoms question types

402 questions across 7 question groups — pick any mix to generate a Physics paper with step-by-step answer keys.

402
Questions
7
Question groups
5
Question types
Sample Questions

Atoms questions

One sample from each question group in this chapter. Select any group above to see the full set with answer keys.

Q 1M.C.Q (1 Marks)1 Mark
Which of the following statements is not correct according to Rutherford model?
  • A
    Most of the space inside an atom is empty.
  • B
    The electrons revolve around the nucleus under the influence of coulomb force acting on them.
  • C
    Most part of the mass of the atom and its positive charge are concentrated at its centre.
  • ✓
    The stability of atom was established by the model.

Answer: D.

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Q 2M.C.Q (1 Marks)1 Mark
Consider aiming a beam of free electrons towards free protons. When they scatter, an electron and a proton cannot combine to produce a H-atom:
  • A
    Because of energy conservation.
  • B
    Without simultaneously releasing energy in the from of radiation.
  • ✓
    A and B both
  • D
    Because of angular momentum conservation.

Answer: C.

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Q 4M.C.Q (1 Marks)1 Mark
An ionised H-molecule consists of an electron and two protons. The protons are separated by a small distance of the order of angstrom. In the ground state:
  • A
    The electron would not move in circular orbits.
  • B
    The energy would be $(2)^4$ times that of a H-atom.
  • C
    The electrons, orbit would go arround the protons.
  • ✓
    A and C both

Answer: D.

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Q 5M.C.Q (1 Marks)1 Mark
When an atomic gas or vapour is excited at low pressure, by passing an electric current through it then?
  • ✓
    Emission spectrum is observed.
  • B
    Absorption spectrucm is observed.
  • C
    Band spectrum is observed.
  • D
    Both $(b)$ and $(c).$

Answer: A.

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Q 6Assertion (A) & Reason (B) MCQ1 Mark
For question two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  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. A is false and R is also false.
Assertion (A): Fraunhofer lines are observed in the spectrum of the sun.
Reason (R): The different elements have different spectra.
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Q 7Assertion (A) & Reason (B) MCQ1 Mark
For question two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  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. A is false and R is also false.
Assertion (A): For the scattering of $\alpha$-partides at a large angles, only the nucleus of the atom is responsible.
Reason (R): Nucleus is very heavy in comparison to electrons.
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Q 8Assertion (A) & Reason (B) MCQ1 Mark
For question two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  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. A is false and R is also false.
Assertion (A): According to classical theory, the proposed path of an electron in Rutherford atom model will be circular.
Reason (R): According to electromagnetic theory an accelerated particle continuously emits radiation
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Q 9Assertion (A) & Reason (B) MCQ1 Mark
For question two statements are given-one labelled Assertion $(A)$ and the other labelled Reason $(R).$ Select the correct answer to these questions from the codes $(a), (b), (c)$ and $(d)$ as given below.
Assertion $(A):$ The positively charged nucleus of an atom has a radius of almost $10^{-15}m.$
Reason $(R):$ In $\alpha$-particle scattering experiment, the distance of closest approach for $\alpha-$particles is $10^{-15}m.$
  • ✓
    Both $A$ and $R$ are true and $R$ is the correct explanation of $A.$
  • B
    Both $A$ and $R$ are true but $R$ is not the correct explanation of $A.$
  • C
    $A$ is true but $R$ is false.
  • D
    $A$ is false and $R$ is also false.

Answer: A.

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Q 10Assertion (A) & Reason (B) MCQ1 Mark
For question two statements are given-one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
  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. A is false and R is also false.
Assertion (A): Smoky flame of Bunsen burner gives continuous spectrum whereas its blue flame gives band spectrum.
Reason (R): The band spectrum consists of coloured bands of light on a dark background.
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Q 111 Marks Question1 Mark
Choose the correct alternative from the clues given at the end of the each statement:
In the ground state of .......... electrons are in stable equilibrium, while in .......... electrons always experience a net force. (Thomson’s model/ Rutherford’s model.)
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Q 121 Marks Question1 Mark
Answer the following questions, which help you understand the difference between Thomson’s model and Rutherford’s model better.Keeping other factors fixed, it is found experimentally that for small thickness t, the number of α-particles scattered at moderate angles is proportional to t. What clue does this linear dependence on t provide?
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Q 131 Marks Question1 Mark
Answer the following questions, which help you understand the difference between Thomson’s model and Rutherford’s model better.
In which model is it completely wrong to ignore multiple scattering for the calculation of average angle of scattering of α-particles by a thin foil?
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Q 141 Marks Question1 Mark
Answer the following questions, which help you understand the difference between Thomson’s model and Rutherford’s model better.
Is the probability of backward scattering (i.e., scattering of α-particles at angles greater than 90°) predicted by Thomson’s model much less, about the same, or much greater than that predicted by Rutherford’s model?
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Q 151 Marks Question1 Mark
Choose the correct alternative from the clues given at the end of the each statement:
The positively charged part of the atom possesses most of the mass in .......... (Rutherford’s model/ both the models.)
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Q 162 Marks Questions2 Marks
Define the distance of closest approach. An α-particle of kinetic energy 'K' is bombarded on a thin gold foil. The distance of the closest approach is 'r'. What will be the distance of closest approach for an α-particle of double the kinetic energy?
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Q 172 Marks Questions2 Marks
Suppose you are given a chance to repeat the alpha-particle scattering experiment using a thin sheet of solid hydrogen in place of the gold foil. (Hydrogen is a solid at temperatures below 14 K.) What results do you expect?
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Q 182 Marks Questions2 Marks
The radius of the innermost electron orbit of a hydrogen atom is $5.3 \times 10^{-11} \mathrm{m}$. What are the radii of the n = 2 and n = 3 orbits?
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Q 192 Marks Questions2 Marks
If Bohr’s quantisation postulate (angular momentum $=\text{nh}/\pi$) is a basic law of nature, it should be equally valid for the case of planetary motion also. Why then do we never speak of quantisation of orbits of planets around the sun?
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Q 213 Marks Question3 Marks
Obtain the first Bohr’s radius and the ground state energy of a muonic hydrogen atom [i.e., an atom in which a negatively charged muon $(\mu)$ of mass about $207m_e$ orbits around a proton].
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Q 223 Marks Question3 Marks
The total energy of an electron in the first excited state of the hydrogen atom is about –3.4 eV.
  1. What is the kinetic energy of the electron in this state?
  2. What is the potential energy of the electron in this state?
  3. Which of the answers above would change if the choice of the zero of potential energy is changed?
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Q 233 Marks Question3 Marks
A difference of 2.3 eV separates two energy levels in an atom. What is the frequency of radiation emitted when the atom make a transition from the upper level to the lower level?
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Q 253 Marks Question3 Marks
In accordance with the Bohr’s model, find the quantum number that characterises the earth’s revolution around the sun in an orbit of radius $1.5 \times 10^{11} m$ with orbital speed $3 \times 10^4 m/s.$ (Mass of earth $= 6.0 \times 1024$ kg.)
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Q 265 Marks Questions5 Marks
The gravitational attraction between electron and proton in a hydrogen atom is weaker than the coulomb attraction by a factor of about $10^{–40}$. An alternative way of looking at this fact is to estimate the radius of the first Bohr orbit of a hydrogen atom if the electron and proton were bound by gravitational attraction. You will find the answer interesting.
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Q 285 Marks Questions5 Marks
Classically, an electron can be in any orbit around the nucleus of an atom. Then what determines the typical atomic size? Why is an atom not, say, thousand times bigger than its typical size? The question had greatly puzzled Bohr before he arrived at his famous model of the atom that you have learnt in the text. To simulate what he might well have done before his discovery, let us play as follows with the basic constants of nature and see if we can get a quantity with the dimensions of length that is roughly equal to the known size of an atom $(~ 10^{–10}m).$
  1. Construct a quantity with the dimensions of length from the fundamental constants e, $m_e$, and c. Determine its numerical value.
  2. You will find that the length obtained in (a) is many orders of magnitude smaller than the atomic dimensions. Further, it involves c. But energies of atoms are mostly in non-relativistic domain where c is not expected to play any role. This is what may have suggested Bohr to discard c and look for ‘something else’ to get the right atomic size. Now, the Planck’s constant h had already made its appearance elsewhere. Bohr’s great insight lay in recognising that h, me, and e will yield the right atomic size. Construct a quantity with the dimension of length from h, $m_e,$ and e and confirm that its numerical value has indeed the correct order of magnitude.
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Q 295 Marks Questions5 Marks
Obtain an expression for the frequency of radiation emitted when a hydrogen atom de-excites from level n to level (n – ncy of revolution of the electron in the orbit.
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Q 305 Marks Questions5 Marks
A hydrogen atom initially in the ground level absorbs a photon, which excites it to the n = 4 level. Determine the wavelength and frequency of photon.
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Q 31Case study (4 Marks)4 Marks
When the electron orbiting in hydrogen atom in its ground state moves to the third excited state, show how the de Broglie wavelength associated with it would be affected.
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Q 32Case study (4 Marks)4 Marks
  1. The figure shows the plot of binding energy (BE) per nucleon as a function of mass number A. The letters A, B, C, D and E represent the positions of typical nuclei on the curve. Point out, giving reasons, the two processes (in terms of A, B, C, D and E), one of which can occur due to nuclear fission and the other due to nuclear fusion.
  1. Identify the nature of the radioactive radiations emitted in each step of the decay process given below.
$^{A}_{Z}\text{X}\rightarrow ^{A-4}_{Z-2}\text{Y}\rightarrow ^{A-4}_{Z-1}\text{W}$.
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Q 33Case study (4 Marks)4 Marks
In the study of Geiger-Marsdon experiment on scattering of α particles by a thin foil of gold, draw the trajectory ofα−particles in the Coulomb field of target nucleus. Explain briefly how one gets the information on the size of the nucleus from this study. From the relation $R = R_0\ A^{1/3},$ where $R_0$ is constant and A is the mass number of the nucleus, show that nuclear matter density is independent of A.
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Q 35Case study (4 Marks)4 Marks
Suppose in an imaginary world the angular momentum is quantized to be even integral multiples of $\frac{\text{h}}{2\pi}$ What is the longest possible wavelength emitted by hydrogen atoms in visible range in such a world according to Bohr's model?
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