Atomic Nucleus [PDF]
Madhyamik Physical Science
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WB Madhyamik Physical Science Atomic Nucleus Notes
The atomic nucleus is the central part of an atom, where most of the mass and positive charge are concentrated. It consists of protons and neutrons, which are collectively called nucleons.
The number of protons in the nucleus determines the atomic number and the identity of the element. The number of neutrons in the nucleus determines the isotope of the element.
The mass number of an atom is the sum of the number of protons and neutrons in the nucleus.
The atomic nuclei are held together by a strong nuclear force, which is one of the four fundamental forces of nature. The strong nuclear force acts only over a very short distance, about the size of a nucleus. It is much stronger than the electromagnetic force, which is responsible for the attraction and repulsion between charged particles. The electromagnetic force acts over a longer distance and tends to push the protons apart in the nucleus. Therefore, the stability of a nucleus depends on the balance between these two forces.
Some nuclei are more stable than others, depending on their proton-to-neutron ratio and their mass number. Some nuclei can undergo radioactive decay, which is a spontaneous process of changing into another nucleus by emitting particles or radiation.
There are three main types of radioactive decay:
- alpha decay,
- beta decay, and
- gamma decay.
Alpha decay involves the emission of an alpha particle, which is a helium nucleus with two protons and two neutrons.
Beta decay involves the emission of an electron or a positron, which are negatively and positively charged particles respectively.
Gamma decay involves the emission of a gamma ray, which is a high-energy electromagnetic radiation.
Radioactive decay can change the identity and properties of an element. It can also release a lot of energy, which can be used for various purposes such as nuclear power generation and nuclear weapons. However, radioactive decay can also pose health and environmental risks, as it can damage living cells and cause mutations or cancers. Therefore, it is important to handle radioactive materials with care and dispose of them safely.
Important Questions on Madhyamik Physical Science Chapter 7 Atomic Nucleus and radioactivity
17 Most Important MCQ with answers on Madhyamik Physical Science
- Which rays have the highest ionizing potential?
(a) a rays
(b) B rays
(c) Y rays
(d) Light rays
Ans. (a) rays.
- The principle of the atomic bomb is –
(a) Electromagnetic effect
(b) Nuclear fusion
(c) Nuclear fission
(d) Chemical reactions
Ans. (c) Nuclear fission.
- Which element is formed when a ray is emitted from uranium?
(a) Radium
(b) Calcium
(c) Thorium
(d) Plutonium
Ans. (c) Thorium.
- Radium was extracted
(a) From graphite
(b) From Diamond
(c) From charcoal
(d) From pitch blend
Ans. (d) From pitch blend.
- The charge radioactive rays were discovered by:
(a) By Prof. Currie
(b) by Madame Curie
(c) by Rutherford.
(d) by Henri Becquerel
Ans. (c) by Rutherford
- α particles are-
(a) Electron
(b) Electromagnetic radiation
(c) Helium nucleus
(d) Only one proton
Ans. (c) Helium nucleus.
- A nucleus of 92U²³⁵ has several protons and neutrons respectively
(a) 92, 235
(b) 92, 143
(c) 235, 92
(d) 143,92
Ans. (b) 92, 143
- The disposal of emissions from nuclear power plants is a major problem. Which of the following is the reason for this?
(a) Highly flammable
(b) Extremely heavy
(c) Odor
(d) Highly radioactive
Ans. (d) Highly radioactive.
- If the nucleus of a radioactive substance emits an a-particle, then
(a) Atomic number decreases. The mass number increases
(b) Atomic number increases, the mass number decreases
(c) Both the atomic number and mass number increase.
(d) Both the atomic number and mass number decrease.
Ans. (d) Both the atomic number and mass number decrease.
- If a B particle is emitted from a radioactive substance, then the atomic number is-
(a) 1 unit folds
(b) increases by 1 unit.
(c) 2 units decrease
(d) increases by 2 units
Ans. (b) increases by 1 unit.
- Which of the following is an uncontrolled chain reaction of nuclear fission?
(a) Nuclear reaction
(b) Atomic bomb
(c) Solar reaction
(d) None of these
Ans. (b) Atomic bomb.
- Which of the following has a negative electric charge?
(a) In alpha rays
(b) In beta rays.
(c) In gamma rays
(d) None of these
Ans. (b) In beta rays.
- Which of the following is positively charged?
(a) In alpha rays
(b) in beta rays
(c) In gamma rays
(d) None of these
Ans. (a) In alpha rays.
- Which is the neutral one?
(a) Alpha rays
(b) Beta rays
(c) Gamma rays
(d) None of these
Ans. (c) Gamma rays.
- Due to which phenomenon do stars radiate light energy?
(a) Nuclear fusion
(b) Nuclear fission
(c) Nuclear reduction
(d) None of these
Ans. (a) Nuclear fusion.
- The speed equal to the speed of light is:
(a) of alpha rays
(b) of gamma rays
(c) of beta rays
(d) None of these
Ans. (b) of gamma rays.
- What is the source of the excessive heat energy of stars?
(a) Nuclear fission
(b) Nuclear fusion
(c) Nuclear division
(d) None
Ans. (b) Nuclear fusion.
15 Most Important 1 mark questions with answers on Madhyamik Physical Science
- Which ray among B and Y rays has the worst effect on human beings?
Answer: Y-ray has the worst effect on humans.
- What type of charge particles is the source of a ray?
Answer: Source of positive charge particles a.
- What type of charge is the source of the particles a.
Answer: Radiation is the source of cation particles.
- From which part of the atom do alpha particles come out?
Answer: From the nucleus of the atom.
- What type of nuclear reaction takes place inside the Sun and the stars?
Answer: Nuclear fusion takes place in the Sun and the stars.
- What is the effect on the free energy per nucleon when the mass number (Proton + Neutron) in the nucleus increases?
Answer: On the mass number of the nucleus, the value of binding energy first increases but then decreases.
- Which rays emanating from radioactive elements cause maximum biological damage?
Answer: Y rays emanating from radioactive elements cause maximum biological damage.
- When a particle is emitted from a radioactive element, its atomic number increases by one.
Answer: When a B particle is emitted from a radioactive element, its atomic number increases by one.
- What is the unit of radioactivity?
Answer: Curie
- What happens to the mass number of a gamma particle when it is emitted from a radioactive element?
Answer: There is no change in the atomic number and mass number of gamma rays when emitted.
- In which form mass defect is released in nuclear fission?
Ans. Binding energy
- Neutrons that initiate nuclear fission are called –
Ans. Thermal neutrons
- What is the S. I. unit of radioactivity?
Ans. The SI unit of radioactivity is the Curie.
- State whether the statement is true or false: ‘Radioactivity’ is the property of the nucleus of an atom.
Ans. Correct.
- State whether the statement is true or false: Alpha ray never creates fluorescence on a photographic plate.
Ans. false
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