1 Marks Question

Question 11 Mark

Choose the correct alternative from the clues given at the end of the each statement:
A classical atom based on .......... is doomed to collapse. (Thomson’s model/ Rutherford’s model.)

Answer

A classical atom based on Rutherford's model is doomed to collapse.

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Question 21 Mark

Choose the correct alternative from the clues given at the end of the each statement:
The size of the atom in Thomson’s model is .......... the atomic size in Rutherford’s model. (much greater than/ no different from/ much less than.)

Answer

The sizes of the atoms taken in Thomson's model and Rutherford's model have the same order of magnitude.

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Question 31 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?

Answer

Scattering is mainly due to single collisions. The chances of a single collision increases linearly with the number of target atoms. Since the number of target atoms increase with an increase in thickness, the collision probability depends linearly on the thickness of the target.

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Question 41 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?

Answer

much less

The probability of scattering of α-particles at angles greater than 90° predicted by Thomson's model is much less than that predicted by Rutherford's model.

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Question 51 Mark

Answer the following questions, which help you understand the difference between Thomson’s model and Rutherford’s model better.
Is the average angle of deflection of α-particles by a thin gold foil predicted by Thomson’s model much less, about the same, or much greater than that predicted by Rutherford’s model?

Answer

about the same
The average angle of deflection of α-particles by a thin gold foil predicted by Thomson's model is about the same size as predicted by Rutherford's model. This is because the average angle was taken in both models.

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Question 61 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.)

Answer

The positively charged part of the atom possesses most of the mass in both the models.

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Question 71 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.)

Answer

In the ground state of Thomson's model, the electrons are in stable equilibrium. However, in Rutherford's model, the electrons always experience a net force.

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Question 81 Mark

Choose the correct alternative from the clues given at the end of the each statement:
An atom has a nearly continuous mass distribution in a .......... but has a highly non-uniform mass distribution in .......... (Thomson’s model/ Rutherford’s model.)

Answer

An atom has a nearly continuous mass distribution in Thomson's model, but has a highly non-uniform mass distribution in Rutherford's model.

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Question 91 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?

Answer

Thomson's model
It is wrong to ignore multiple scattering in Thomson's model for the calculation of average angle of scattering of α-particles by a thin foil. This is because a single collision causes very little deflection in this model. Hence, the observed average scattering angle can be explained only by considering multiple scattering.

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Question 101 Mark

Define ionisation energy. What is its value for a hydrogen atom?

Answer

Minimum energy required to free an electron from the ground state. Its value for hydrogen atom is 13.6 eV.

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Question 111 Mark

What is the ratio of radii of the orbits corresponding to first excited state and ground state in a hydrogen atom?

Answer

$\text{r}\propto\text{n}^{2}\therefore\frac{\text{r}_{1}}{\text{r}_{2}} = 4:1.$

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Question 121 Mark

Write the second hypothesis of the Bohr Model of hydrogen atom.

Answer

It states that an electron can revolve only in those orbits for which its angular momentum is an integral multiple of $h / 2 \pi$(i.e.,$m v r=n h / 2 \pi)$.

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Question 131 Mark

Imagine removing one electron from He⁴ and He³. Their energy levels, as worked out on the basis of Bohr model will be very close. Explain why:

Answer

Bohr model is applicable for hydrogen atom-and some lighter atoms in which a single electron revolves around a stationary nucleus of positive charge Ze (called hydrogen like atom). If we remove one electron from He⁴ and He³, atoms contain one electron and becomes hydrogen like atoms. Now we can apply Bohr model to define the energy levels.

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Question 141 Mark

The Bohr radius is given by $\text{a}_0=\frac{\in_0\text{h}^2}{\pi\text{me}^2}$ Verify that the RHS has dimensions of length.

Answer

$\text{a}_0=\frac{\in_0\text{h}^2}{\pi\text{me}^2}=\frac{\text{A}^2\text{T}^2\big(\text{ML}^2\text{T}^{-1}\big)^{2}}{\text{L}^2\text{ML}^{-2}\text{M(AT)}^2}$
$\text{a}_0=\frac{\text{M}^2\text{L}^2\text{T}^{-2}}{\text{M}^{2}\text{L}^{3}\text{T}^{-2}}=\text{L}$
$\therefore$ a₀ has the dimensions of length.

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Question 151 Mark

Cathode rays constitute a stream of:

Electrons
Protons
Positive ions
Negative ions.

Answer

Electrons

Explanation:

Cathode ray consists of fast moving charged particle. When electric and magnetic fields are applied to the cathode ray in the discharge tube, the rays are deflected thus establishing that they consist of charged particles. the direction of deflection show that cathode rays consist of negatively charged particle called electrons.

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