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Test: Nuclei


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30 Questions MCQ Test Physics Class 12 | Test: Nuclei

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Test: Nuclei - Question 1

What percentage of the mass of an atom is concentrated in the nucleus?

Detailed Solution for Test: Nuclei - Question 1

More than 99.99% of the mass of any atom is concentrated in its nucleus. If the mass of protons and neutrons (which are in the nucleus of every atom) is approximately one atomic mass unit, then the relative mass of an electron is 0.0005 atomic mass units.

Test: Nuclei - Question 2

In the mass number range A = 30 to 170, the binding energy per nucleon is

Detailed Solution for Test: Nuclei - Question 2

The binding energy is a very short order range force.
So beyond a certain amount of range the force has no influence beyond that. that's why after
certain number the binding energy per nucleon do not change even if we add more nucleons.

Test: Nuclei - Question 3

Plutonium decays with a half-life of 24000 years. If the plutonium is stored for 72000 years, then the fraction of plutonium that remains is    

Detailed Solution for Test: Nuclei - Question 3

t1/2​=24000 yrs
It is stored for 3 half-lives.
Fraction remaining is (1/2​)3=1/8

Test: Nuclei - Question 4

In a nuclear reaction which of the following is conserved

Test: Nuclei - Question 5

Cadmium rods are used in a nuclear reactor for

Detailed Solution for Test: Nuclei - Question 5

In nuclear reactors, fission of uranium is carried out by bombarding  a slow moving neutron on uranium which results in emission of 3 more neutrons along with the byproducts  So, cadmium rods are used to absorb extra neutrons in order to achieve controlled chain reaction.

Test: Nuclei - Question 6

In what units is mass measured on the atomic scale?

Detailed Solution for Test: Nuclei - Question 6

The atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as daltons, D). The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope.

Test: Nuclei - Question 7

Energies associated with nuclear processes are

Detailed Solution for Test: Nuclei - Question 7

Unlike a chemical reaction, a nuclear reaction results in a significant change in mass and an associated change of energy, as described by Einstein’s equation. Nuclear reactions are accompanied by large changes in energy, which result in detectable changes in mass. The change in mass is related to the change in energy according to Einstein’s equation: ΔE = (Δm)c2. Large changes in energy are usually reported in kiloelectronvolts or megaelectronvolts (thousands or millions of electronvolts). With the exception of 1H, the experimentally determined mass of an atom is always less than the sum of the masses of the component particles (protons, neutrons, and electrons) by an amount called the mass defect of the nucleus. The energy corresponding to the mass defect is the nuclear binding energy, the amount of energy released when a nucleus forms from its component particles. In nuclear fission, nuclei split into lighter nuclei with an accompanying release of multiple neutrons and large amounts of energy. The critical mass is the minimum mass required to support a self-sustaining nuclear chain reaction. Nuclear fusion is a process in which two light nuclei combine to produce a heavier nucleus plus a great deal of energy.

Test: Nuclei - Question 8

B210has a half life of 5 days. The time taken for seven-eighth of a sample to decay is

Detailed Solution for Test: Nuclei - Question 8

Half-life of Bi210=5 days
∴k= 0.693/(t1/2) ​=(0.693/5) ​day−1
Using k=(2.303/t)​ log (a/a-x)
(where a = a0​, (let) ⇒x=7/8 ​a0​, t is time taken in decay and k is rate constant)
We get, t=(2.303×5/0.693)log a0​/(1/8)a0​​
= (2.303×5/0.693) ​log8=15days
 

Test: Nuclei - Question 9

If 10% of a substance decays in 10 days, then approximate percentage of substance left after 24 days is

Detailed Solution for Test: Nuclei - Question 9

Given, 10% of substance decays in 10 days
So, let [A]o=100, [A]t=100-10=90
So, K=(2.303/t) log ([A]o/[A]t)
K= (2.303/10) log (100/90)
K= (2.303/10) (log10-log9)
K= (2.303/10)91-0.9542)     [log9=0.9542]
K= (2.303/10) x 0.0458 day-1
So, after 24 days,
t= (2.303/K) log (100/[A]t)
24=2.303x10/2.303x0.0458) log [100/[A]t]
log[100/[A]t]=(24x0.0458)/10=0.1099
100/[A]t=antiog(0.1099)=1.288
So, [A]t=100/1.288≈100/1.3
[A]t=76.9≈77%
The closest answer is 78% which is option A. So the correct answer would be option A
 

Test: Nuclei - Question 10

Choose the WRONG statement. A thermonuclear fusion reactor is better than a fission reactor for the following reason:

Test: Nuclei - Question 11

A free neutron decays into

Detailed Solution for Test: Nuclei - Question 11

Neutron is unstable outside the nucleus.
It's decaying equation is given below.
0​n111​H+0−1e+v

Test: Nuclei - Question 12

The disintegration energy is

Test: Nuclei - Question 13

A radioactive substance has a half life of four months. Three fourths of the substance will decay in

Detailed Solution for Test: Nuclei - Question 13

Substance left undecayed, N0​−(3/4)​N0​=(1/4)​N0
N/N0​ ​=1/4​=(1/2​)n
 
∴ Number of atoms left undecided, n=2 i.e, in two half-lives
∴ t=nT=2×4=8 months

Test: Nuclei - Question 14

At a given time there are 25% undecayed nuclei in a sample. After 10 seconds number of undecayed nuclei reduces to 12.5%. Then mean life of the nuclei will be about

Detailed Solution for Test: Nuclei - Question 14

Half-life of radioactive sample, i.e., the time in which the number of undecayed nuclei becomes half (T) is 10 s.
Mean life, τ=T/loge​2=10s/0.693=1.443×10=14.43s ≈ 15s

Test: Nuclei - Question 15

Which of the following particles can be added to the nucleus of an atom without changing its chemical properties?

Detailed Solution for Test: Nuclei - Question 15

When neutrons are added to the nucleus of an atom its chemical properties remain unchanged because the atomic number of particles remains the same. But when electron, proton or alpha particles are added, atomic number changes so chemical properties change.

Test: Nuclei - Question 16

Relation between atomic number (Z), neutron number (N) and mass number (A) is

Test: Nuclei - Question 17

α-rays are

Detailed Solution for Test: Nuclei - Question 17

Alpha particles, also called alpha rays or alpha radiation, consist of two protons and two neutrons bound together into a particle identical to a helium-4 nucleus. They are generally produced in the process of alpha decay, but may also be produced in other ways.

Test: Nuclei - Question 18

The half life of radon is 3.8 days. After how many days will only one twentieth of a radon sample be left over?

Detailed Solution for Test: Nuclei - Question 18

Let the initial amount of radon be N0​ and the amount left after t days be N which is equal to N0​/2

Test: Nuclei - Question 19

90% of a radioactive sample is left undisintegrated after time τ has elapsed, what percentage of initial sample will decay in a total time 2τ?

Detailed Solution for Test: Nuclei - Question 19

Given that 90% is left un-decayed after time 't'.
Hence, 10% decays in time 't'.
Initially assume that the amount of substance is 'x'
After time 't' 10% is decayed.
i.e. Amount of substance left =0.9x
After further time 't' another 10% is decayed.
i.e. 0.1×0.9x is decayed 
Leaving behind 0.81x.
Hence after time 2t we see that 0.19x has decayed, which is 19%.
 

Test: Nuclei - Question 20

The average number of neutrons released by the fission of one uranium atom is

Detailed Solution for Test: Nuclei - Question 20

Fission also results in the production of several neutrons, typically two or three. On the average, about 2.5 neutrons are released per unit and the energy of a neutron released per fission of a uranium atom are 2 MeV. 

Test: Nuclei - Question 21

The nuclei of isotopes of a given element contain the same number of

Detailed Solution for Test: Nuclei - Question 21

An isotope is one of two or more forms of the same chemical element. Different isotopes of an element have the same number of protons in the nucleus, giving them the same atomic number, but a different number of neutrons giving each elemental isotope a different atomic weight.

Test: Nuclei - Question 22

β -rays and γ-rays are respectively

Detailed Solution for Test: Nuclei - Question 22

Beta radiation ~ Stream of electrons (unit negative charge). Beta positive radiation is when a positron is emitted rather than an electron.
Gamma radiation ~ Electromagnetic radiation of very short wavelength = high photon energy.

Test: Nuclei - Question 23

Nuclear fusion is possible

Detailed Solution for Test: Nuclei - Question 23

Nuclear fusion is possible only between light nuclei as they become more stable by acquiring greater atomic number to form particles with intermediate mass. Nuclear fission is possible with heavy nuclei.

Test: Nuclei - Question 24

What is the main source of energy of the sun?

Detailed Solution for Test: Nuclei - Question 24

Like most stars, the sun is made up mostly of hydrogen and helium atoms in a plasma state. The sun generates energy from a process called nuclear fusion. During nuclear fusion, the high pressure and temperature in the sun's core cause nuclei to separate from their electrons.

Test: Nuclei - Question 25

All nuclides with same mass number A are called

Detailed Solution for Test: Nuclei - Question 25

Nuclides which have the same number of  protons are called isotopes. When nuclides have the same mass, numbers are called isobars. When nuclides have same number of neutron are called isotones. When the elements have the same molecular formula but have different arrangements of atoms in space are called isomers.  

Test: Nuclei - Question 26

When a hydrogen bomb explodes, which of the following is used?

Detailed Solution for Test: Nuclei - Question 26

The hydrogen bomb is a nuclear weapon that uses a mixture of fission and fusion to produce a massive explosion.
The nuclear fission generates enough heat to initiate the nuclear fusion reaction. After that, the nuclear fusion releases enormous amounts of energy, making the hydrogen bomb a lot more powerful than an atomic bomb.

Test: Nuclei - Question 27

The half-life T1/2of a radionuclide is

Detailed Solution for Test: Nuclei - Question 27

The hydrogen bomb is a nuclear weapon that uses a mixture of fission and fusion to produce a massive explosion.
The nuclear fission generates enough heat to initiate the nuclear fusion reaction. After that, the nuclear fusion releases enormous amounts of energy, making the hydrogen bomb a lot more powerful than an atomic bomb.
 

Test: Nuclei - Question 28

A radioactive material decays by simultaneous emission of two particles with respective half lives 1620 and 810 years. The time in years, after which one fourth of the material remains is

Detailed Solution for Test: Nuclei - Question 28

Since, from Rutherford-Soddy law, the number of atoms left after half-lives is given by
N=N0​(1/2​)n
where, N0​ is the original number of atoms.
The number of half-lives, n= time of decay​/effective half−life
Relation between effective disintegration constant (λ) and half-life (T)
λ=ln2/T​
∴λ1​+λ2​= (​ln2/ T1​)+ ​(ln2/ T2​)
Effective half-life,
1/T​=1/T1​​+1/T2​​=(1/1620)​+(1/810)​
1/T​=1+2/1620 ​⇒T=540yr
∴n=T/540
∴N=N0​(1/2​)t/540⇒N/N0​​=(1/2​)2=(1/2​)t/540
⇒t/540​=2⇒t=2×540=1080yr

Test: Nuclei - Question 29

The chemical behavior of an atom depends upon

Detailed Solution for Test: Nuclei - Question 29

The chemical behavior of atoms is determined by the number and the configuration of the electrons in the atom. The number of protons in the nucleus determines the number of electrons in the atom.

Test: Nuclei - Question 30

Nuclear mass M is found to be

Detailed Solution for Test: Nuclei - Question 30

The actual mass is always less than the sum of the individual masses of the constituent protons and neutrons because energy is removed when the nucleus is formed. This energy has mass, which is removed from the total mass of the original particles.

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