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Published on: 29/08/2019
Atoms and Nuclei
Download CBSE Class 12th Standard CBSE Physics question papers, sample papers, important questions, and previous year solved papers in PDF format. Get free study materials, NCERT solutions, and exam preparation resources for Class 12th Standard CBSE Physics
Questions + Answers key
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1.
O2 molecule consists of two oxygen atoms.In the molecule, nuclear force between the nuclei of the two atoms
is not important because nuclear forces are short-ranged
is as important as electrostatic force for binding the two atoms
cancels the repulsive electrostatic force between the nuclei
is not important because oxygen nucleus have equal number of neutrons and protons.
2.
For the ground state, the electron in the H-atom has an angular momentum =h, 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,
because only one of these would have a minimum energy
because only one of these would have a minimum energy
angular momentum must be in the direction of spin of electron
because electrons go arround only in horizontal obits.
3.
Taking the Bohr radius as a0 = 53pm, the radius of Li++ ion its ground state, on the basis of Bohr's model, will be about
53pm
27pm
18pm
13pm
4.
The half life of a radioactive substance in 30 days. What is the time taken for ¾ of its original mass to disintegrate?
5.
which have greater ionizing power:α-particles or \(\beta\)-particles?
6.
Two nuclei have mass numbers in the ratio 1:8.What is the ratio of their nuclear radii?
7.
which observation led to the conclusion in the \(\alpha\)-particle scattering exp. That atom has vast empty space?
8.
what conclusions were drawn from the observation in which few alpha-particle were seen rebounding from gold foil?
9.
Write the relation for (i) the distance of closest approach and (ii) impact parameter.
10.
Can a hydrogen atom absorb a photon whose energy exceeds its binding energy?
11.
How is impact parameter related to the scattering angle?
12.
In Rutherford's alpha ray scattering experiment, why most of alpha particles pass through almost unscattered.
13.
Why did Thomson atom model fail?
1.
(a)
is not important because nuclear forces are short-ranged
2.
(a)
because only one of these would have a minimum energy
3.
(c)
18pm
4.
N/No = (1/2)n
t = 2T = 2 x 30 = 60 days
5.
\(\)α - particles have more ionizing power than β - particles
6.
\(R=R_0 A^{1 / 3}, R_1 / R_2=A_1^{1 / 3} / A_2^{1 / 3}=1,{ }^{1 / 3} / 27_{1 / 3}=1 / 3\)
7.
A larger number of alpha particle went through undeflected
8.
The entire positive charge and the mass were concentrated at one place inside the atom, called the nucleus.
9.
\(\text { (i) } \quad r_0=\frac{Z_e(2 e)}{4 \pi \epsilon_0\left(\frac{1}{2} m v^2\right)}\)
\(\text { (ii) } b=\frac{1}{4 \pi \epsilon_0} \frac{Z e^2 \cot \quad \theta / 2}{\left(\frac{1}{2} m v^2\right)}\)
10.
Yes, it can absorb.
11.
\(b=\frac{Z e^2 \cot \quad \theta / 2}{4 \pi \epsilon_0\left(\frac{1}{2} m v^2\right)}\)
12.
This is because there is a lot of empty space between the nucleus and revolving electrons in the atom.
13.
This model could not explain scattering of \(\alpha\) particle through large angles.
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