# +2 Physics Unit 8 - Nuclear Physics

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Prepared by P. ILAIYARAJA M. Sc.,B. Ed., PG ASST IN PHYSICS , GHSS, PANCHANATHIKKULAM EAST, NAGAI DT.
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• 1.

• A.

(2)

• B.

(1)

• C.

(3)

• D.

(4)

A. (2)
• 2.

### The nuclei are example of

• A.

Isotones

• B.

Isomers

• C.

Isotopes

• D.

isobars

A. Isotones
Explanation
Isotones are nuclei that have the same neutron number but different atomic numbers. Therefore, they belong to the same isotope family. In this question, the answer "isotones" is correct because it correctly identifies the nuclei as having the same neutron number, but potentially different atomic numbers.

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• 3.

### The mass defect of a certain nucleus is found to be 0.03 amu. Its binding energy is

• A.

27.93 MeV

• B.

27.93 eV

• C.

27.93 GeV

• D.

27.93 KeV

A. 27.93 MeV
Explanation
The mass defect of a nucleus is the difference between the mass of the nucleus and the sum of the masses of its individual protons and neutrons. It represents the mass that is converted into energy during the formation of the nucleus. The binding energy of a nucleus is the energy required to separate all of its individual protons and neutrons. The binding energy is directly related to the mass defect, as given by Einstein's equation E=mc^2. Since the mass defect is given as 0.03 amu, the binding energy can be calculated using the conversion factor 1 amu = 931.5 MeV. Therefore, the binding energy is 0.03 amu * 931.5 MeV/amu = 27.93 MeV.

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• 4.

### Nuclear fission can be explained by

• A.

Liquid drop model

• B.

Quark model

• C.

Shell model

• D.

Bohr atom model

A. Liquid drop model
Explanation
The liquid drop model is a theoretical model that explains nuclear fission by comparing the nucleus to a drop of liquid. According to this model, the nucleus is composed of nucleons (protons and neutrons) that are held together by attractive nuclear forces. The model suggests that the nucleus behaves like a liquid drop, with a surface tension that keeps it in a spherical shape. When a heavy nucleus absorbs a neutron, it becomes unstable and can split into two smaller nuclei, releasing a large amount of energy. This process is known as nuclear fission, and the liquid drop model provides a useful framework for understanding it.

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• 5.

### The nucleons in a nucleus are attracted by

• A.

Nuclear force

• B.

Magnetic force

• C.

Gravitational force

• D.

Electrostatic force

A. Nuclear force
Explanation
The correct answer is nuclear force. The nucleons in a nucleus, which include protons and neutrons, are attracted to each other by the strong nuclear force. This force is responsible for holding the nucleus together despite the repulsive electrostatic force between protons. The nuclear force is much stronger than the other forces listed, such as the gravitational force and magnetic force, and is specifically designed to act on subatomic particles within the nucleus.

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• 6.

### The ionisation power is maximum for

• A.

α – particles

• B.

γ – rays

• C.

β − particles

• D.

Neutrons

A. α – particles
Explanation
α-particles have the highest ionization power because they are heavy and carry a double positive charge. As they travel through a medium, they interact strongly with the electrons in the atoms, causing a large number of ionizations and excitations. This high ionization power makes α-particles highly damaging to living tissues and materials. In contrast, γ-rays, β-particles, and neutrons have lower ionization power because they are either neutral or have lower mass and charge, resulting in fewer interactions with atoms in the medium.

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• 7.

### The half life period of a certain radioactive element with disintegration constant 0.0693 per day is

• A.

10 days

• B.

14 days

• C.

140 days

• D.

1.4 days

A. 10 days
Explanation
The half-life of a radioactive element is the time it takes for half of the substance to decay or disintegrate. The disintegration constant is a measure of how quickly this decay occurs. In this question, the disintegration constant is given as 0.0693 per day. To find the half-life, we need to find the time it takes for the substance to decay by half, which is when the disintegration constant multiplied by the time equals 0.5. Solving this equation, we find that the time is approximately 10 days. Therefore, the correct answer is 10 days.

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• 8.

### The radio-isotope used in agriculture is

• A.

(2)

• B.

(3)

• C.

(4)

• D.

(1)

A. (2)
Explanation
The radio-isotope used in agriculture is option (2). However, without the options provided, it is not possible to determine the specific radio-isotope used in agriculture.

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• 9.

### The average energy released per fission is

• A.

200 MeV

• B.

200 meV

• C.

200 GeV

• D.

200 eV

A. 200 MeV
Explanation
The correct answer is 200 MeV. MeV stands for mega-electron volts, which is a unit of energy commonly used in nuclear physics. The average energy released per fission is typically in the range of millions of electron volts, and 200 MeV falls within this range. The other options (200 meV, 200 GeV, and 200 eV) are either too small or too large to represent the average energy released per fission.

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• 10.

### The explosion of atom bomb is based on the principle of

• A.

uncontrolled fission reaction

• B.

Controlled fission reaction

• C.

Fusion reaction

• D.

Thermonuclear reaction

A. uncontrolled fission reaction
Explanation
The explosion of an atom bomb is based on the principle of uncontrolled fission reaction. In this process, the nucleus of a heavy atom, such as uranium or plutonium, is split into two smaller nuclei, releasing a large amount of energy. This energy is released in the form of an explosion. The fission reaction is uncontrolled because it occurs rapidly and uncontrollably, leading to a chain reaction and a large release of energy. This is different from a controlled fission reaction, where the reaction is controlled and sustained in a nuclear reactor. Fusion reaction and thermonuclear reaction involve the merging of atomic nuclei and are not applicable to atom bomb explosions.

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• 11.

• A.

(3)

• B.

(2)

• C.

(1)

• D.

(4)

A. (3)
• 12.

### In the nuclear reaction ,  X-stands for

• A.

Neutron

• B.

Proton

• C.

Electron

• D.

Deutron

A. Neutron
Explanation
In the context of a nuclear reaction, X typically represents a neutron. Neutrons are subatomic particles that have no charge and are found in the nucleus of an atom. They play a crucial role in nuclear reactions, as they can be absorbed by atomic nuclei, causing them to become unstable and undergo radioactive decay. The other options, proton, electron, and deutron, do not typically represent X in a nuclear reaction.

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• 13.

### In β – decay

• A.

Neutron number decreases by one

• B.

Atomic number decreases by one

• C.

mass number decreases by one

• D.

Proton number remains the same

A. Neutron number decreases by one
Explanation
In β- decay, a neutron in the nucleus is converted into a proton, emitting an electron and an antineutrino. As a result, the neutron number decreases by one, while the atomic number increases by one due to the addition of a proton. The mass number, which represents the total number of protons and neutrons in the nucleus, remains the same as the mass of a proton is approximately equal to the mass of a neutron. Therefore, the correct answer is that the neutron number decreases by one.

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• 14.

### Isotopes have

• A.

Same proton number but different neutron number

• B.

Same proton number and neutron number

• C.

Same mass number but different atomic number

• D.

Same neutron number but different proton number

A. Same proton number but different neutron number
Explanation
Isotopes are atoms of the same element that have the same number of protons (proton number) but different numbers of neutrons (neutron number). This means that they have the same atomic number (the number of protons) but different mass numbers (the sum of protons and neutrons). Isotopes can have different physical and chemical properties due to the difference in their neutron numbers, which affects their stability and nuclear properties.

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• 15.

### The time taken by the radioactive element to reduce to 1/e times is

• A.

Mean life

• B.

Half life/2

• C.

Half life

• D.

Twice the mean life

A. Mean life
Explanation
The mean life of a radioactive element is the average time it takes for half of the atoms in a sample to decay. Therefore, it can be inferred that it would take the element the same amount of time to reduce to 1/e (approximately 0.368) times its original amount. This is because 1/e is approximately equal to 0.368, which is half of 0.736 (the remaining amount after one mean life). Therefore, the correct answer is mean life.

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• 16.

### The half life period of is 10.1 minute. Its life time is

• A.

(4)

• B.

(3)

• C.

(2)

• D.

(1)

A. (4)
Explanation
The half-life period of a substance is the time it takes for half of the substance to decay or disappear. In this case, the half-life period is 10.1 minutes. This means that after 10.1 minutes, half of the substance will have decayed. Therefore, the lifetime of the substance, or the time it takes for it to completely decay, would be longer than the half-life period. Therefore, the correct answer is (4), indicating that the lifetime of the substance would be longer than 10.1 minutes.

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• 17.

### Positive rays of the same element produce two different traces in a Bainbridge mass spectrometer. The positive ions have

• A.

Different mass with same velocity

• B.

Different mass with different velocity

• C.

Same mass with same velocity

• D.

Same mass with different velocity

A. Different mass with same velocity
Explanation
The fact that the positive rays of the same element produce two different traces in a Bainbridge mass spectrometer indicates that the positive ions have different mass. The fact that they have the same velocity suggests that the difference in the traces is not due to differences in velocity, but rather due to differences in mass. Therefore, the correct answer is different mass with same velocity.

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• 18.

### The binding energy of  nucleus is

• A.

493 MeV

• B.

8.8 MeV

• C.

88 MeV

• D.

41.3 MeV

A. 493 MeV
Explanation
The binding energy of a nucleus refers to the amount of energy required to completely separate all the nucleons (protons and neutrons) within the nucleus. It represents the strength of the nuclear force that holds the nucleus together. The correct answer of 493 MeV suggests that it requires 493 million electron volts of energy to completely separate all the nucleons in the nucleus. This value indicates a large binding energy, indicating a stable and tightly bound nucleus.

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• 19.

### The ratio of nuclear density to the density of mercury is about

• A.

(3)

• B.

(2)

• C.

(4)

• D.

(1)

A. (3)
Explanation
The ratio of nuclear density to the density of mercury is about 3. This means that the nuclear density is approximately three times greater than the density of mercury.

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