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Physics 1 Marks Question

Atoms · Gujarat Board (GSEB) STD 12 Science (GSEB - English Medium). 21 questions.

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Question 11 Mark
The nucleus of atom is responsible for $\alpha$-particle scattering with large angle, why does not the electron?
Answer
Mass of electron is less than the helium, therefore according to conservation law of momentum, it cannot scattered the $\alpha$-particle at large angle.
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Question 21 Mark
What is emission spectrum?
Answer
When any matter is heated then obtained spectrum from emitted light is called emission spectrum.
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Question 31 Mark
For normal state of atom, quantum number $n=1$. What is the value of $n$ for ionised state?
Answer
$n=\infty$
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Question 41 Mark
What do you find, if the total energy of electron is zero?
Answer
Zero energy means electron is at infinite distance from the nucleus or it is only free.
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Question 51 Mark
In Rutherford's experiment, why the mass of nucleus not important?
Answer
In Rutherford's scattering experiment, charge on the nucleus is reason of scattering. Electrostatic field is main cause for scattering. Therefore scattering is force from the mass of nucleus.
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Question 61 Mark
Why Bohr's orbit is called stable orbit?
Answer
In such type of orbit, neither electron emitts energy nor observed, during the revolution. Therefore, these orbits are called stable orbits.
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Question 71 Mark
Write the values of kinetic energy ( K ) and potential energy (U) of hydrogen atom.
Answer
$K =\frac{e^2}{8 \pi \epsilon_0 r}$ and $U =\frac{-e^2}{4 \pi \epsilon_0 r}$
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Question 81 Mark
Write the relation between orbital radius and electron velocity.
Answer
$
r=\frac{e^2}{4 \pi \epsilon_0 m v^2}
$
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Question 91 Mark
How much is the diameter of hydrogen atom?
Answer
In hydrogen atom, a proton is in the nucleus and an electron revolves around the nucleus with radius of $0.53 \ Å$, so diameter of atom will approximately $1.06 \ Å$.
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Question 111 Mark
The nucleus of atom is responsible for alpha particle scattering with large angle. Why not the electron?
Answer
Mass of electron is less than the helium, therefore according to conservation law of momentum, nucleus cannot scatter it the helium at large angle.
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Question 121 Mark
Write the reason for this event. Most of the electrons passes through the gold foil without deflected.
Answer
Because, most part inside the atom is empty.
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Question 131 Mark
What is Bohr's quantization condition of angular momentum of electron of the atom?
Answer
$m v r=\frac{n h}{2 \pi}, n$ is integer.
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Question 141 Mark
Define the impact parameter.
Answer
The perpendicular distance of the velocity vector of the $\alpha$-particle from the centre of the nucleus, when it is far away from the atom. It is denoted by ' $b$ ',
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Question 151 Mark
Write two results which are obtained from Rutherford's scattering experiment.
Answer
(1) The maximum part of mass and whole charge of atom is concentrated at tiny space called nucleus.
(2) Radius of nucleus of atom is $\frac{1}{10000}$ th part of radius of atom.
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Question 161 Mark
Why gold foil is used in $\alpha$-particle scattering experitment?
Answer
Due to heavy nucleus of gold, deflection of $\alpha$-particle is large, and fine thin foils can be make from it.
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Question 171 Mark
Write any two drawbacks of Rutherford's experiment related to atomic structure.
Answer
(1) It fails to explain the characteristics of line spectra.
(2) It fails to explain the stability of atom.
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Question 181 Mark
What is the reason that the numbers of absorption transitions is less than the emission transition in atom?
Answer
Its reason is that, emission transition stops in any lowest energy level after initiating from any higher energy level, while absorption transition always starts from ground energy level and finishes at highest energy level.
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Question 191 Mark
In Rutherford's scattering model, it is shown that : (i) mostly alpha particle passes direct linearly without scattering, (ii) while some scattered by making large angle and some of these after scattering returned back to their path. What is the information obtained from these about atomic structure?
Answer
(i) Maximum part is empty inside the atom.
(ii) Positive charge is conentrated at tiny space (nucleus) in atom.
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Question 201 Mark
Why, some definite lines of atomic spectrum of matter is obtained?
Answer
There are only definite and discrete energy level of atom. Therefore some definite frequencies are possible of atom.
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Question 211 Mark
Some of $\alpha$-particles out of $\alpha$-particles incident on gold foil, returned back to their path after scattering. Give the reason.
Answer
In any atom, positive charge is concentrated at tiny space inside, which exerted large repulsive force on $\alpha$-particl, so $\alpha$-particle returned back to its path.
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