CHAPTER 2 HDR 102 PHYSICS FOR RADIOGRAPHERS 1 ELECTROSTATICS MR KAMARUL AMIN BIN ABDULLAH SCHOOL OF MEDICAL IMAGING FACULTY OF HEALTH SCIENCE

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1 HDR 102 PHYSICS FOR RADIOGRAPHERS 1 CHAPTER 2 ELECTROSTATICS PREPARED BY: MR KAMARUL AMIN BIN ABDULLAH SCHOOL OF MEDICAL IMAGING FACULTY OF HEALTH SCIENCE

2 LEARNING OUTCOMES At the end of the lesson, the student should be able to:- Define the electrostatic, electrification, and electric charge. Briefly explain the properties of electric charge. Describe the law of electrostatic (Coulomb's Law) Briefly explain what is potential difference. Briefly explain what is electric field and its strength. Slide 2 of 52

3 OUTLINE INTRODUCTION 2.1 Electrostatics Electric Charge Electrostatics Electrification 2.2 Electrostatic Laws 2.3 Electric Potential 2.4 Conducting Properties of Material 2.5 References Slide 3 of 52

4 INTRODUCTION Figure 1 What is electrostatic? Do you know why is it important in x-ray production? CLICK HERE FOR ANSWER Slide 4 of 52

5 INTRODUCTION Figure 2 Where electrons (negative) are travelling towards anode target (positive). Slide 6 of 52

6 2.1 Electrostatics Electric Charge Matter has mass and energy equivalence. It means matter also may have electric charge. Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Figure 3 Slide 7 of 52

7 2.1 Electrostatics Electric Charge Electrons and protons are the smallest units of electric charge. The electron has one unit of negative charge and the proton has one unit of positive charge. Figure 4 Slide 8 of 52

8 2.1 Electrostatics Electric Charge The smallest unit of electric charge is electron. This charge is much too small to be useful, so the fundamental unit of electric charge is the coulomb (c): 1C = 6 x electron charges. Figure 5 Slide 9 of 52

9 2.1 Electrostatics Electrostatics Electrostatics is the study of stationary electric charges. Because of the way atoms are constructed, electrons often are free to travel from the outermost shell of one atom to another atom. Protons, are fixed in the nucleus of an atom and not free to move. Slide 10 of 52

10 2.1 Electrostatics For example, on touching a metal doorknob after having walked across a deep-pile carpet in winter, you get a shock (by contact). It is Figure 6 because electrons are rubbed off the carpet onto your shoes causing you to become electrified. An object is said to be electrified if it has too few or too many electrons. Figure 7 Slide 11 of 52

11 2.1 Electrostatics Electrification It is the process of electron charges being added to or subtracted from an object. For instance, the outer shell electrons of some types of atoms are loosely bound and can be removed easily. Removal of the electrons electrifies the substances from which they were removed and results in static electricity. Slide 12 of 52

12 2.1 Electrostatics Figure 8 For example, if you run a comb through your hair, electrons are removed from the hair and deposited on the comb. The comb become electrified with too many negative charges. Slide 13 of 52

13 2.1 Electrostatics Figure 9 An electrified comb can pick up tiny pieces of paper as though the comb were a magnet. Because of its excess electrons, the comb repels some electrons in the paper, causing the closest end of the paper to become slightly positively charged. This results in a small electrostatic attractive force. Slide 14 of 52

14 2.2 Electrostatic Laws Laws of electrostatics describe how electric charges interact with each other and with neutral objects. Associated with each electric charge is electric field. The electric field points outward from a positive charge. Uncharged particles do not have an electric field. Figure 10: The electric field of positive and negative charges. Slide 15 of 52

15 2.2 Electrostatic Laws SIMILAR electric charges (-ve and ve or +ve and +ve) electric fields are in opposite direction, repel to each other. Figure 11: It shows the like +ve charges are repelling each other. Figure 12: It shows the like ve charges are also repelling each other. Slide 16 of 52

16 2.2 Electrostatic Laws UNLIKE electric charges (-ve and +ve) electric fields radiate in same direction, attract each other. The attraction and repulsion between charges is due to electric field as it is called electrostatic force. Figure 13: Unlike charges will attract each other. Slide 17 of 52

17 2.2 Electrostatic Laws Figure 14: It shows the different types of interactions between positive and negative charges. Slide 18 of 52

18 2.2 Electrostatic Laws Coulomb's law states that the electrical force between two charged objects is directly proportional to the product of the quantity of charge on the objects and inversely proportional to the square of the separation distance between the two objects. Figure 15: The distance will affect the electrical force between charges. Figure 16: Coulomb. Slide 19 of 52

19 2.2 Electrostatic Laws In equation form, Coulomb's law can be stated as:- Q1 = the quantity of charge on object 1 (in Coulombs), Q2 = the quantity of charge on object 2 (in Coulombs), d = the distance of separation between the two objects (in meters). k = is a proportionality constant known as the Coulomb's law constant. (9.0 x 10 9 N m 2 / C 2 ) medium= air Slide 20 of 52

20 2.3 Electric Potential Electric charges have potential energy. When it is positioned close to each other, like electric charges have electric potential energy because they can do work when they fly apart. Electron bunched up at one end of wire create an electric potential because the repulsive force causes some electrons to move along the wire so that work can be done. <CLICK HERE> Slide 21 of 52

21 2.3 Electric Potential The unit of electric potential is the volt (V). Electric potential is sometimes called voltage (the higher the voltage, the greater potential to do work). X-ray imaging systems usually require 220 V or higher. The volt is potential energy/unit charge, or joule/coulomb (1 V = 1 J/C) CLICK TO SEE AN EXAMPLE Slide 23 of 52

22 2.4 Conducting Properties of Materials Insulators are materials in which electric charge does not move easily They can be charged, but charge doesn t move well Glass, rubber, plastic, wood, and paper are examples Figure 19 Slide 25 of 52

23 2.4 Conducting Properties of Materials Conductors are materials in which electric charge moves easily a) When an area becomes charged, charge distributes itself over entire surface b) Copper, aluminum, and silver are examples c) Charge will remain on conductor Figure 20 if you hold it with an insulator Slide 26 of 52

24 2.4 Conducting Properties of Materials Semiconductors are materials that have electrical properties somewhere between conductors and insulators. Figure 21 Silicon and Germanium are examples. Figure 22 Slide 27 of 52

25 Activity 1 Test Your Knowledge Answer the question. Electrons travel from one object to another when they are rubbed against one another. Which process of electrification is this? A B C Contact Induction Friction Slide 28 of 52

26 SUMMARY Electric charge is a physical property of matter that causes it to experience a force when near other electrically charged matter. Electrostatics is the study of stationary electric charges. Electrification is the process of electron charges being added to or subtracted from an object. SIMILAR electric charges (-ve and ve or +ve and +ve) electric fields are in opposite direction, repel to each other. UNLIKE electric charges (-ve and +ve) electric fields radiate in same direction, attract each other. Coulomb's Law states that the electrical force between two charged objects Slide 32 of 52

27 NEXT SESSION PREVIEW CHAPTER 3: CAPACITOR In chapter 3, students will learn about the capacitor and its functions in x-ray circuit. Slide 33 of 52

28 2.5 References No. REFERENCES 1 Ball, J., Moore, A. D., & Turner, S. (2008). Essential physics for radiographers. Blackwell. 2 Bushong, S. C. (2008). Radiologic science for technologists. Canada: Elsevier. Slide 34 of 52

29 APPENDIX FIGURE Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 SOURCE Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure Slide 35 of 52