# Class 10th Physics Unit 18 Question An Answer

## Class 10th Physics Unit 18 Question An Answer On Newsongoogle By Bilal Articles

Q 1. Define atom and write down its parts.

Ans: The smallest part of an element is called an atom. Parts of atom: Atom consists of two parts and its central part is called nucleus. The nucleus consists of protons and neutrons. The proton ls a positively charged particle and neutron has no charge so the nucleus carries a positive charge. The electrons revolve around the nucleus ln nearly circular orbits. Since an atom ls a neutral particle, so the number of electrons in it is equal to the number of protons.

Q 2. What are Nucleons?

Ans: The mass of the proton & neutron is nearly the same i.e. 1.67 x 1027 kg. Since the protons and neutrons exist inside the nucleus so these are called nucleons.

Q 3. What is Atomic Mass Number?

Ans: A nucleon is nearly 1836 times heavier than an electron. So the mass of an atom is nearly equal to the total sum of the masses of all the protons and neutrons present in the nucleus of that atom. “The total number of protons and neutrons in the nucleus is called the Atomic Mass Number and is denoted by the letter A”.

Q 4. What is Atomic Number?

Ans: Since the number of protons in an atom of different elements is different so the number of protons in the nucleus indicates the charge on that nucleus. “The number of protons ln a nucleus is called the charge number or Atomic number and is denoted by the letter Z”. The number of neutrons in the nucleus is denoted by the letter N.

Q 5. What do you know about Nuclide?

Ans: If atomic number of an atom is Z and its Atomic Mass Number is A then this atom is represented by the symbol which is called a nuclide ZX A . For example, there is only one proton in the nucleus of hydrogen atom so its atomic number is 1 and its atomic mass is also 1. Hence it is denoted by 1H 1 .

Q 6. What is the difference between Atomic number and Atomic Mass number?

Ans: Atomic Number: The total number of protons and neutron in the nucleus is called the atomic mass number. It is denoted by the Latter A. Atomic Mass Number: The number of protons in a nucleus is called the charge number or atomic number. It is denoted by the letter Z. Q 7. What are radioactive isotopes? Ans: The atoms of the same radioactive element whose atomic numbers are the same but have different atomic mass numbers are called Radioactive isotopes.

Q 7. What are isotopes? What do they have in common and what are there differences.

Ans: Atoms of the same element having name atomic number but different mass number, are called isotope. They have same chemical properties but different physical properties.For example, Hydrogen has three isotopes: Protium Z = 1, A = 1, N = A – Z = 0 Detitrium Z = 1, A = 2, N = A – Z = 1 Tritium Z = 1, A = 3, N = A – Z = 2 Hence, from above relations we conclude that the number of protons are same and number of neutrons are different ln the isotopes of hydrogen.

Q 8. Why Marie Curie and Pierre are famous?

Ans: The most significant investigations of the process of radioactivity were done by Marie Curie and the husband Pierre. They discovered two new elements which emitted radiations. These were named polonium and radium. This process of emission of radiations by some elements was called natural radioactivity by Marie Curie.

Q 9. Why are heavy nuclei unstable?

Ans: Heavy nuclei are unstable due to large number of protons. The strong nuclear force cannot balance the repulsive Coulomb force which comes into play due to increase in size.

Q 10. What is meant by Background Radiations?

Ans: Background Radiations: “Radiations present in atmosphere due to different radioactive substances are called background radiations”. Sources of background radiations: The back ground radiation present in the atmosphere is due to the following two possible causes: i. The presence of radioactive material under the earth ii. The cosmic rays entering the earth from the upper atmosphere along with the sun light.

Q 11. What are cosmic radiation?

Ans: The earth and all living things on it also receive radiation from outer space. This radiation is called cosmic radiation which primarily consists of positively charged ions from protons to iron and large nuclei. The cosmic radiation interacts with atom in the atmosphere to create, a shower of secondary radiation, including x-rays, muons, protons, alpha particles, electrons and neutrons.

Q 12. Describe a brief account of Interaction of various types of radiations with matter.

Ans: α-radiation: It is a helium nucleus. When an alpha particle passes through a gas it interacts with the atom of the gas and ionizes them. As its mass is comparatively more than β and ɣ so it has less penetrating power. Each ionization by an α –particle produces an ion pair. The range of α particle is around 7cm and it can be stopped by a thick paper. Α particle are capable of producing fluorescence in zinc sulphide or barium platinocyanide. β-Radiations: these are negative charge particles they can penetrate 100 times more than α-particles. The β- particles loses most its energy in a single collision. Β- Particle can also produce fluorescence in some materials like barium platinocyanide. ɣ-Radiations: ɣ-rays have no charge that is why the cause very little ionization. The ɣ-ray photon can be absorbed by an atom and a photo electron can be ejected (photoelectric effect). When fast moving ɣ-ray photon is stopped it disintegrates into an electron positron pair (pair production). Material having large no of electron in a unit volume absorbs more ɣ-radiations. They have high penetration power than α & β particles and their intensity decreases exponentially with increase in depth of penetration into the material.

Q 13. Explain how α and β -particles may ionize an atom without directly hitting the electrons? What is the difference in the action of the two particles for producing ionization?

Ans: Since α and β particles are electrically charged they can cause ionization without hitting an atom either by attracting or repelling the electrons of the target atom. α particle produces ionization by exerting electrostatic force of attraction while β-particles produce ionization by exerting electrostatic force of repulsion. α-particles cause ionization by attracting the electron while β particles cause ionization by repelling the electron.

Q 14. A particle which produces more ionization is less penetrating why?

Ans: A particle which produces more ionization interacts strongly with the matter and loses its energy in a short distance and hence comes to rest soon, that’s why it is less penetrating.

Q 15. If someone accidentally swallows an α-source and a β-source which would be the more dangerous to him? Explain why?

Ans: α-particles have greater ionizing power as compare to β-particles. So, they can cause more damage to tissues, if swallowed.

Q 16. Do α, β and ɣ Radiations emit from the same element? Why they are found in many radioactive elements?

Ans: α, β and ɣ rays emit from the same element. But, an element cannot emit α and β rays simultaneously. When a radioactive element emits α and β rays, it decays into new element and so on. Hence, we find all the three radiations in many radioactive elements.

Q 17. Define nuclear transmutation?

Ans: “The spontaneous process in which a parent unstable nuclide changes into a more stable daughter nuclide with the emission of radiations is called nuclear transmutation”.

Q 18. What is the use of α, β and ɣ radiation?

Ans: α particles: They are used to treat skin cancer because their penetrating power is small. β particles: They are used to treat the tumors under the skin due to their large penetration power. ɣ particles: They are used to treat the infection in interior parts of the body clue to their longest penetration power. Q 22. What is the difference between an electron and β-particles? Ans: β particle is negatively charged particle emitted from the nucleus of radioactive element. An electron is negatively charge particle which revolves around the nucleus.

Q 19. What do you know about half life?

Ans: “The half-life of an element is that time during which the numbers of atoms of that element are reduced to one half’. Example: If the life time of a radioactive element is T, then at the end of this time the number of atoms in this element remain one half, after a time 2T, the number of atoms remain 25% and after time 3T, the number of atoms are reduced to 12.5% of initial number.

Q 20. What is meant by Penetrating ability?

Ans: Penetrating ability: The strength of radiations to penetrate a certain material is called penetrating power”. All kind of radiations penetrate but perpetrating range is different for each.

Q 21. What are radioactive isotopes?

Ans: The atoms of the same radioactive element whose atomic numbers are the same but have different atomic mass numbers are called Radioactive Isotopes.

Q 22. What are stable nuclides?

Ans: Nuclei which do not emit radiations naturally are called stable nuclei. Most of the nuclei whose atomic number is from 1 to 82 are stable nuclei: They do not change from one type of element to another. The stable elements can also be changed into unstable form by bombarding them with neutrons. Such elements are called, radio isotopes.

Q 23. What are unstable nuclides’?

Ans: Nuclei which do not emit radiations naturally are called stable nuclei. Some elements, whose atomic number is greater than 82, are naturally unstable. These elements depending upon their characteristics, emit, all the time, different types of radiations and they continuously change from one type of element to another.

Q 24. What is a radioactive tracer? Describe one application each in medicine, agriculture and industry.

Ans: A definite quantity of radio isotope introduced into a mechanical or biological system to enable its route through the system, as: i. Tracers are widely used in medicine to detect malignant tumors, blockage in the blood vessels, e.g. brain and thyroid tumors are detected using I-131. Radio sodium has been largely used in medical research to study the action of various medicines ii. Tracers are also used in agriculture to study the uptake of a fertilizer by a plant, e.g. P-32 is incorporated in fertilizer and added to the soil. iii. Tracer technique is also very useful in industry in detecting the cracks and leakage in the pipes and welding joints e.g. Iridium-192 is used to test the welds.

Q 25. How can Radioactivity helps in the Treatment of Cancer?

Ans: Medical applications of radio isotopes can be divided into two parts i.e. diagnostic and therapy. Some examples are as: i. Radiotherapy with ɣ-rays from cobalt-60 is often used in the treatment of cancer. The ɣ- rays are carefully focused on the malignant tissue. ii. Radioactive Iodine-131 is used to fight with cancer of the thyroid gland. iii. For Skin Cancer Phosphorus-32 or Strontium-90 may be used. They produce β radiation.

Q26. How can radioactivity help in the treatment of Cancer?

Ans: Radioactivity & Treatment of Cancer: Cancerous cells are always weak as compared to the normal cells, and hence are destroyed by firing β-radiation or ɣ-radiation from radioactive source. Sometimes encapsulated “seeds” made from radioactive source are implanted in the malignant tissues for local and short ranged treatment. For example: • ɣ -rays from Co-60 in general • Iodine-131 for treatment of cancer of thyroid gland. • Phosphorus-32 or strontium-90 may be used for skin-cancers.

Q 27. How a radioisotope be used to determine the effectiveness of fertilizer?

Ans: Radioactive phosphorus or nitrogen used as a tracer in agriculture, provide information about the best fertilizer to supply to a particular crop and, soil. Due to their use, varieties of crops such as rice, wheat and cotton have improved. Moreover, plants have shown more resistance to disease and give better yield and grain quality.

Q 28 What is Positron?

Ans: Positron is a particle with mass equal to the mass of an electron having opposite and equal charge.

Q 29. What is means by Nuclear fission.

Ans: Nuclear Fission: Nuclear fission takes place when a heavy nucleus, such as U- 235, splits or fissions, into two smaller nuclear by bombarding a slow moving (low- energy) neutron represent in equation.

Q 30. Why does water is used to slow down the neutrons rather than lead?

Ans: When neutrons collide with lead nuclei, they are bounced back. While lead atoms remain at rest due to their greater mass. But, I case of water, collision between neutrons and hydrogen nuclei, present is water is perfectly elastic. In this collision. Neutrons are slowed down, while proton starts moving.

Q 31. Write a note on Einstein’s mass energy equation.

Ans: ln classical physics, the various form of energy was related under the law of conservation of energy but no relationship was established between the energy and mass. In 1905, when Einstein gave his theory of relativity, it also contained the idea that the energy and matter are interchangeable. For this change an equation was also given which is known as Einstein’s mass- energy equation. It is E = mc2 Which means that if mass m of matter is converted into energy, then this will be equal to E, where in this mass-energy equation c is the speed of light that is 3 x 108 ms-1

Q 32. What is do you know about Fission chain reaction Fission chain reaction.

Ans: When a neutron reacts with a uranium nucleus, two or three neutrons are released. Every one of these reacts with next nuclei producing two or three more neutrons and hence, the number of available neutrons and the fission goes on increasing. Such a reaction is called the chain reaction.

Q 33. Define Fusion Reaction.

Ans: When two light nuclei combine to form a heavier nucleus, the process is called nuclear fusion”. Equation: If an atom of Deuterium is fused with an atom of Tritium, a Helium nucleus or alpha particle is formed as given:

Q 34. Why it is more difficult to start a fusion reaction rather than fission reaction?

Ans: Because, in bringing two nuclei closer to each other, great work has to be done against repulsive forces of nuclei. Hence, more energy is needed. On the other hand, fission may be proceeded with slow neutrons.

Q 35. Discuss uses and the hazards of radiations.

Ans: Some of harmful effects on human beings due to large doses or prolonged small doses of radiations. i. Radiation burns, mainly due to beta and gamma radiations, which may cause redness and sores on the skin. ii. Sterility (i.e. inability to produce children). iii. Genetic mutations in both human and plants. Some children are born with serious deformities. iv. Leukernia (Cancer of the blood cells) v. Blindness or formation of cataract in the eye.

Q 36. Describe the precaution to minimize radiations dangers (safety measures) Precautions to minimize radiation dangers.

Ans: Because we cannot detect radiations directly, we should strictly follow safety precautions, even when the radioactive sources are very weak. i. Sources should not be handled with tongs and for ceps. ii. The user should use rubber gloves and hand should be washed carefully after the experiment. iii. All radioactive sources should be stored in thick lead containers. iv. Never point radioactive source towards a person. v. Frequent visits to the radiation sensitive areas should be avoided.

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