Nuclear & Radioactivity — Set 3
Physics · नाभिकीय और रेडियोधर्मिता · Questions 21–30 of 50
A nuclear chain reaction is said to be critical when the multiplication factor k is?
Correct Answer: A. Equal to 1
The correct answer is 'Equal to 1'. Option A is correct because k = 1 means the reaction sustains at a steady rate. If k is less than 1, the reaction dies out, and if greater than 1, it grows. Reactors aim to keep k close to 1 for control.
The main purpose of a moderator in a nuclear reactor is to?
Correct Answer: D. Slow down fast neutrons
Option D is correct because a moderator reduces neutron speed to increase fission probability in many reactors. Slower neutrons are called thermal neutrons. Common moderators include graphite and heavy water.
Control rods in a nuclear reactor are mainly used to?
Correct Answer: B. Absorb excess neutrons
Option B is correct because control rods absorb neutrons to regulate the chain reaction. Materials like cadmium or boron are good neutron absorbers. By inserting or withdrawing rods, reactor power is controlled.
In a nuclear power plant, a coolant is mainly used to?
Correct Answer: A. Remove heat from the reactor core
Option A is correct because coolant carries away heat produced in the core. This heat is later used to produce steam to run turbines. Water, carbon dioxide, or liquid metals can act as coolants in different designs.
Nuclear binding energy is the energy required to?
Correct Answer: B. Separate a nucleus into its nucleons
Option B is correct because binding energy is the energy needed to break the nucleus into protons and neutrons. It is related to the stability of the nucleus. Binding energy per nucleon is often used to compare stability.
In the equation E = mc^2, the symbol c represents?
Correct Answer: A. Speed of light in vacuum
Option A is correct because c is the speed of light in vacuum. This relation shows mass can be converted into energy. Even a small mass corresponds to a large amount of energy.
One electron-volt (1 eV) is defined as the energy gained by an electron when it moves through a potential difference of?
Correct Answer: B. 1 volt
Option B is correct because 1 eV corresponds to an electron accelerated through 1 volt. It is a convenient unit for atomic and nuclear energies. 1 eV is much smaller than 1 joule.
The energy equivalent of 1 atomic mass unit (1 u) is approximately?
Correct Answer: D. 931 MeV
Option D is correct because 1 u corresponds to about 931 MeV of energy. This comes from converting mass to energy using E = mc^2. This value is widely used in nuclear calculations.
Nuclear force between nucleons is generally?
Correct Answer: C. Strong and short-range
Option C is correct because nuclear force is very strong but acts over very short distances. It binds protons and neutrons inside the nucleus. At larger distances, it becomes negligible compared to electromagnetic force.
The neutron was discovered by?
Correct Answer: B. James Chadwick
Option B is correct because James Chadwick identified the neutron. Neutrons have no charge but contribute to nuclear mass. The discovery helped explain isotopes and nuclear structure.