© 2001-2005 shannon w. helzer. all rights reserved. unit 11 charge and...

Download © 2001-2005 Shannon W. Helzer. All Rights Reserved. Unit 11 Charge and Coulomb’s Law

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2001-2005 Shannon W. Helzer. All Rights Reserved. Unit 11 Charge and Coulombs Law Slide 2 2001-2005 Shannon W. Helzer. All Rights Reserved. The Atom Atoms are composed of three particles: neutrons, protons, and electrons. The nucleus of the atom is made up of the protons and the neutrons. The electrons orbit about the nucleus. The negatively charged electrons are attracted to the positively charged protons. The neutrons act as spaces between the like-charged protons. These charge interactions are responsible for the atom staying together. 11-1 Slide 3 2001-2005 Shannon W. Helzer. All Rights Reserved. Ions An atom with the same number of positive charges and negative charges is said to be neutrally charged. If the atom looses an electron, then it will have one more positive charge than it has negative charges. Therefore, it has a net positive charge and is known as a cation. If the atom gains an electron, then it will have one more negative charge than it has positive charges. Therefore, it has a net negative charge and is known as a anion. Either way, both species are known as ions. 11-2 Slide 4 2001-2005 Shannon W. Helzer. All Rights Reserved. Charge Repulsion Like charges repel one another. Watch the electroscope below as a negatively charged rod is brought close by. The electrons in the rod repel those on the metal plate. They in turn travel down to the needle and axel apparatus. Here they repel one another causing the needle to rotate. 11-3 Slide 5 2001-2005 Shannon W. Helzer. All Rights Reserved. Charge Attraction Like charges repel; however, opposite charges attract. Charging by induction demonstrates both at the same time. The net result of charging by induction leaves a positive net charge on one sphere and a negative net charge on the other. 11-4 Slide 6 2001-2005 Shannon W. Helzer. All Rights Reserved. More Charge Repulsion and Attraction Water molecules are known as polar molecules. This statement means that they have a positive and a negative end. Watch what happens on the molecular level as a positively charged rod is brought near to an ordinary glass of water. The negative end of the water molecule is attracted to the positively charged rod causing the H 2 O molecules to rotate and align. 11-5 Slide 7 2001-2005 Shannon W. Helzer. All Rights Reserved. Grounding When a negatively charged rod is brought into close position to a metallic sphere, a charge separation occurs. If a switch connected to the ground is opened, then the electrons will flow from the sphere into the ground. The elimination of charge in this manner is known as grounding. Your house is electrically grounded in order to prevent injury or fire. 11-6 Slide 8 2001-2005 Shannon W. Helzer. All Rights Reserved. Coulombs Law A law used to determine how much force of attraction or repulsion exist between two charged particles. F C = _________________ with units of ______________________ k = _________________ with units of ______________________ q 1 & q 2 = _________________ with units of ______________________ d or r= _________________ with units of ______________________ The remaining slides will demonstrate the procedure used in conjunction with Coulombs Law. 11-7 Slide 9 2001-2005 Shannon W. Helzer. All Rights Reserved. WS 51 #1 Three charges are aligned as shown (note the scale on the graph). The distance between q 1 and q 2 is 0.04 m and the distance between q 3 and q 2 0.02 m. a. Make a guess. Do you think that charge q 2 will be attracted towards q 1 or q 3. Why? b. Calculate the force on q 2 due to q 1. Do not forget the direction. c. Calculate the force on q 2 due to q 3. Do not forget the direction. d. What is the net force (magnitude and direction) on q 2 ? e. Does your answer verify your guess in part a? 11-8 Slide 10 2001-2005 Shannon W. Helzer. All Rights Reserved. WS 51 #2 Due to the fact that the charges in this problem all lie on a straight line, this problem is done exactly like WS 51 #1. However, note the fact that q 2 and q 3 have different charges in this problem. Also, make sure you pay attention to the scale and convert it to the proper units. 11-9 Electric Charge Positions Scale: 1 Square = 0.05m q1q1 q3q3 q2q2 Slide 11 2001-2005 Shannon W. Helzer. All Rights Reserved. WS 51 #3 The charges in this problem are not on a straight line. As a result, you must use analytical vector addition (Unit 6). You must use trig in order to determine the angle between q1 and q2. You must use the Pthag in order to find the distance between q 1 and q 2. 11-10 Scale: 1 Square = 0.5 cm q1q1 q3q3 q2q2 VectorMagnitudeAnglex componenty componentQuad -------------- Slide 12 2001-2005 Shannon W. Helzer. All Rights Reserved. WS 52 #1 For problems like this one you will need to use trig in order to find the angles between both sets of charges. Always remember that the angles should be based upon 0 being to the right along the +x axis. 11-11 Scale: 1 Square = 1.0 cm q1q1 q3q3 q2q2 VectorMagnitudeAnglex componenty componentQuad -------------- Slide 13 2001-2005 Shannon W. Helzer. All Rights Reserved. WS 51 #4 A pie pan is placed on top of a Van de Graaff machine as shown. Once the machine is turned on, the pie pan hovers at a distance of 1.5 cm above the machine. If the charge on the top surface of the Van de Graaff machine (q1) is C and the charge on the pie pan is C, then calculate the mass of the pie pan. 11-12 Slide 14 2001-2005 Shannon W. Helzer. All Rights Reserved. This presentation was brought to you by Where we are committed to Excellence In Mathematics And Science Educational Services. Slide 15 A AA 11-1 VectorMagnitudeAnglex componenty componentQuad -------------- Slide 16 2001-2005 Shannon W. Helzer. All Rights Reserved. A AA 11-1

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