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Page 1 of 7 Grade 10S Physics T3W5 material 1-Sample Questions 1. How do we determine the half-life of a certain radioactive substance from the graph of mass remaining vs. time? How do we determine the half-life from the graph of activity versus time? 2. What are the factors that affect the rate of radioactive decay? 3. Give some examples of the uses of radioactivity A slightly radioactive sample of fertilizer is put in the soil. As the plant absorbs the fertilizer, the plant itself becomes slightly radioactive. The radioactivity in the fertilizer will affect the absorption of the fertilizer; how? A slightly radioactive sample of fertilizer is put in the soil. As the plant absorbs the fertilizer, the plant itself becomes slightly radioactive. Which radiations would be most useful for the radioactive fertilizer to emit ? 4. G-M tubes can be used to follow the paths of atoms in chemical or biochemical reactions. Where in a leaf is magnesium used? If lead accumulates in the body until it kills, which part of the body does it destroy, and where is it stored? Are atoms of iodine able to leave solid iodine into a saturated solution of iodine? 5. When rocks form, a certain amount of radioactive material is locked up in them. What is an essential property of this radioactive material for it to be useful in radioactive dating? 6. Give all the possible harmful effect of exposure to radioactivity. 7. What is the average dose of radiation likely to be received by a person in the course of a lifetime? Is there a minimum dose that would never have any harmful effect? Explain. 8. Radiation can be used to kill cancerous growths. What are the side effects of using such a technique rather than performing a surgical operation for example? 9. a) b) c) How is the amount of energy produced in nuclear reactors controlled? What is this energy and in what way is it used to produce energy? In what ways is fission different from radioactive decay? 10. What is the greenhouse effect? What oxide is mainly responsible for this and what does this effect lead to? What is acid rain? What oxide is responsible for this and what are some of the harmful effects of acid rain? What are the advantages of nuclear energy over energy from fossil fuels? SABIS® Proprietary Page 2 of 7 11. What are the disadvantages of nuclear energy? 12. When the nuclear waste materials are to be buried safely, what important factor must be taken into consideration? Why? Sample Questions Solutions 1‐ Take two points of coordinates (t,m) and (t’,m’) where m’=m/2 then get t’‐t Take two points of coordinates (t,A) and (t’,A’) where A’=A/2 then get t’‐t 2‐ Quantity and type of the material. 3‐ Uses of radioactivity: Tracing, thickness measurement, radioactive dating, medicine, luminous scales, food irradiation and insect control. If a radioactive salt is given to a plant, and later radioactivity is detected in the leaves but not in the stem. Not only does this reveal where it is used but it also allows us to find how quickly it is absorbed and what steps of chemical reactions it goes through. 4‐ Tracers are used to tell where in a leaf magnesium is used If a radioactive magnesium salt is given to a plant, and later radioactivity is detected in the leaves but not in the stem, we can find out how quickly it was absorbed and what steps of chemical reactions it went through. Radioactive labeling can be used in crime detection. 5‐ By measuring in the rocks the present rate of radioactivity or the concentration of the non radioactive products of radioactivity, the age of the rock can be determined. 6‐ a. Lower doses may cause Leukemia within 2years or other forms of cancer 15 to 20 years. b. Radiation can cause genetic aberrations which will result in many early death or life long illnesses and can be inherited by future generations. c. Very high doses can cause immediate death or death within weeks. d. Damage from radiation can result in falling hair and sores that take long time to heal. 7‐ The average dose of radiation that a person is likely to receive in the course of a lifetime from natural sources is about 10rads. No one has the correct answer on how much radiation is harmful and the risk of death or disease from cancer is not the same for all people and is statistical in nature. 8‐ Exposing a cancer victim to a limited and localized dose of radiation can kill the cancerous growth and at the same time have the harmful effect of causing cancer in the future. 9‐ a. by controlling the concentration of radioactive materials, the quantity and speed of the neutrons, the rate of fission and the amount of energy produced can be controlled. b. In power plant nuclear energy is produced. Water or gas circulates around the reactor and takes away the heat which can be used to turn turbines. c. *Neutrons are given off in fission; not α,β or γ radiations as in radioactivity. *Fission is not spontaneous, unlike radioactive decay. * There are many possible by‐products from fission while a radioactive decay leads to one only immediate by‐product. * Fission can produce heat at a controllably significant rate. Heat from radioactive decay is seldom significant and not controllable. SABIS® Proprietary Page 3 of 7 10‐ Electromagnetic radiation in the form of light rays coming from the sun are absorbed by the Earth and are radiated back as heat. Carbon dioxide in the air is responsible of this. Greenhouse effect leads to global warming. When oxides (oxides of sulfur and nitrogen) in the air dissolve in rain, acidic rains are formed. Acidic rains destroy forests, killing millions of trees and animals, and poisoning many lakes, killing the fish in them. Advantages of nuclear energy over energy from the fossil fuels: Burning fossil fuels produces huge amounts of carbon dioxide which contributes to the greenhouse effect. Fossil fuel ran out, whereas reactors produce their own fuel, so there will never be a shortage. 11‐ Disadvantages of nuclear energy: Cost of building a safe station is high Problem of radioactive waste storage Psychological bias due to previous nuclear accidents and nuclear arms. 12‐ The half life of waste material 2-Homework Basic Questions BGT 1. G (i) What is an alpha particle? What are the properties of Alpha particles? Solution: An alpha particle is a helium nucleus (2 protons + 2 neutrons). Alpha particles: • move in matter in straight lines. • when shot in air, they ionize many air molecules as they pass close to them, i.e. they have a very high ionization power (105 ion-pairs/cm). • affect photographic film and produce fluorescence of ZnS. • can be stopped by a piece of paper or about 5 cm air. • are deviated by magnetic fields. • are emitted at speeds of about 6% of the speed of light. T (ii) Fig.11.1 shows the path of three α-particles moving towards a thin gold foil. gold foil A B C Fig. 11.1 SABIS® Proprietary Page 4 of 7 Particle A is moving directly towards a gold nucleus. Particle B is moving along a line which passes close to a gold nucleus. Particle C is moving along a line which does not pass close to a gold nucleus. (a) On Fig. 11.1, complete the paths of the α-particles A, B and C. (b) State how the results of such experiment, using large numbers of α particles, provide evidence for the existence of nuclei in gold atoms. gold foil Solution: (a) A B C Fig. 11.1 (b) Only few alpha particles are scattered through large angles, most of the alpha particles pass without deviation, which means that the most part of the atom is an empty space. Scattering and repulsion occurs due to the concentrated mass and charge in the nucleus. BGT 2. G (a) Solution: What is a Beta particle? What are the properties of Beta particles? A beta particle is a fast moving electron (it has a charge of –1e). Beta particles: • move in matter in tortuous lines. • when shot in air, they ionize much fewer air molecules than alpha particles. (103 ion-pairs/cm) • are deviated by magnetic fields ; the deflection in a magnetic field is opposite in direction to that of alpha particles initially moving along the same path. • affect photographic film and produce fluorescence of ZnS. • can be stopped by about 1 mm Al or about 5 m air. • are emitted at speeds of up to 98% of the speed of light. SABIS® Proprietary Page 5 of 7 T (b) Solution: B BGT 3. G (a) Solution: Give the nature and properties of Gamma rays. Gamma rays are electromagnetic waves or photons of very high energy. • • • • • • SABIS® Proprietary Gamma rays: move in matter in straight line. are not stopped completely by any material; they can pass through lead. (4cm lead stops 10% of the incident radiation) are not deviated by magnetic fields. affect photographic film and produce fluorescence of ZnS. when shot in air, they ionize very few air molecules, i.e. they have a very low ionization power (10 ion-pairs/cm). are emitted at the speed of light. Page 6 of 7 (b) T Solution: T C (c) Solution: SABIS® Proprietary C Page 7 of 7 Section 7.4 (Pg-100) B 4. Explain how you can distinguish experimentally between the three types of radiation using: (a) a magnetic field and a cloud chamber. Solution: In a cloud chamber, three different tracks of cloud can be seen: • • • (b) Alpha particles leave a bold straight line because of the large number of ions created. Beta particles leave a thin winding track because of their weak ionizing power. The gamma photon produces no tracks; however, the electrons that it knocks out, leave β type tracks. a magnetic field and a vacuum tube. Solution: In the absence of the magnetic field one spot can be seen on the screen; In the presence of the magnetic field, three spots can be noticed on the screen: Alpha and beta are deflected in opposite directions, while gamma rays travel in straight line. B 5. Explain how the G-M tube works and how to measure background radiation using the G-M tube. Solution: SABIS® Proprietary • A single particle of radiation, hitting the tube, creates a pair of ions in the tube, that are attracted to oppositely charged electrodes, creating many other ions in the process. This causes a pulse of electric current, that can increment a counter, be converted into a noise (click), or both. • Background radiation rate = Number of counts/ Time elapsed (in the absence of any radiation source sample).