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PHYS-104 – FUND. OF PHYSICS, II UNIT II (B) ELECTRIC ENERGY and CAPACITANCE Objectives: A. Using the concept of potential difference and potential energy of charges, be able to: (N) 1. (N) 2. (N) 3. (E) 4. (E) 5. (E) 6. (E) 7. (E) 8. (E) *9. (N) B. (N = No Equation Sheet; E = Equation Sheet) define it between two points using a test charge and apply to explain a physical situation, i.e., cathode-ray tube, cell membrane action potential, lightning bolts, sign of charges knowing potential energy charge, etc. solve for one variable in terms of the other two (using proper units) involving potential difference, electric field strength and separation distance. state what physically occurs near equipotential surfaces and draw in equipotential lines near charged bodies. correctly solve problems involving the potential difference between parallel plates, separation distance, and force on a given charge between the plates. solve for any variable such as work done in terms of the: (a) charge, electric field strength, and separation distance. (b) charge and voltage. explain what is meant by "batteries are a source of potential difference" and apply to practical examples. discuss, using physical principles, the outcome involving electric fields and potential difference, i.e., if V = O at a point, must E = O as well? solve for the power needed to pump ions at a given rate against a given potential difference. solve for the number of electrons reaching a CRT screen given accelerating potential and power rating. For a given moving charge, solve for the: 1. 2. acceleration given the mass, charge, electrode distance, and potential difference of the field. kinetic energy in electron volts and joules, mass, or speed if given the other variables. Phys104, OBJ, Unit IIB Sp13 - 2 (N) C. In relation to capacitance, be able to identify: 1. 2. 3. 4. D. For capacitors be able to solve for: (E) 1. (N) 2. (E) 3. *4. E. what a capacitor does and the physical principles of its operation in electrical circuits. the effect on capacitance for different dielectrics (especially how they affect the electric field), separation distances and plate area for parallelplate capacitors. practical examples of capacitors. relate dielectric constant, C, Q and V to a parallel plate capacitor and apply to explain a practical situation. the capacitance, dielectric constant, separation distance and/or area of parallel plate capacitors in terms of the other variables. capacitance, charge or voltage in terms of the other two given variables. the energy, capacitance(charge), or voltage given the other variables the work required to pull the plates of a capacitor to a multiple of their original separation. Be able to solve for the: (N) 1. (E) 2. equivalent capacitance of up to five capacitors in series; in parallel. charge across, the potential difference across, and the energy stored across the equivalent capacitance as well as across each capacitor in series and in parallel circuits in (1). LABORATORY OBJECTIVES A. For a given material, be able to classify it as a good conductor, poor conductor, or non-conductor (insulator) and discuss the physical principles involved to substantiate your choice. B. Identify the quantities that charge and potential energy depends upon, what makes charges move in a conductor, and what happens to charges moving through conductors. C. Apply basic principles learned in Objectives A and B to explain the results of a practical situation. Phys104, OBJ, Unit IIB Sp13 - 3 D. Be able to construct a capacitor out of aluminum foil and plastic wrap and connect it to a signal generator and loudspeaker circuit to: 1. 2. identify the relation between frequency and impedance. read an impedance vs frequency graph to answer questions such as what is the frequency of a 5 ohm impedance, etc. Phys104, OBJ, Unit IIB Sp13 - 4 LEARNING ACTIVITIES - ELECTRIC ENERGY Read: Textbooks: College Physics,9thed.,Serway,Chapt 16(skim pp. 555-558, 560-562) College Physics, 11th ed.(Schaum's Outline), pages 281-294 (pps 252-262 in 10th ed.) Optional: Conceptual Physics, pages 425-430 in 10th edition (pages 428-433 in 9th edition) on reserve in Library. Homework: Chapter 16; MC Q’s 2, 9 & 11; Concept Q’s 1, 2, 4, 5, 6, & 10 Problems 1, 3(add What is the energy in eV?), 7,14, 15, 23*, 25(add What is the energy of the charged capacitor?), 33(add Find the potential difference across each capacitor in (a) and (b)), 37*, 45, 51(add calculate the maximum charge on the plates and energy stored in the capacitor in (b))& non-extra credit problems Extra 1: Three capacitors whose capacitances are 5.0, 10.0 and 50 µF are connected in series across a 12.0 V battery. Find the charge on each capacitor and the potential difference across each Extra 2: The three capacitors in Extra 1 are connected in parallel across the same battery. Find the charge on each capacitor and the potential difference across each. Answers to Selected Even-numbered Homework Problems: (14) -9.08 J Extra 1:CT =3.12 µF, Q =37.5 µC, V5 =7.5 V, V10 =3.75 V, V50 =.75 V Extra 2: CT =65 µF; Q5 =60 µC, Q10 =120µC, Q50 =600µC, V = 12 V Audio-Visual Material: Video: Fields Around Point Charges (29 min) Laboratory: Fields and Eqipotentials Charges In Motion - An Investigation of Transfer of Electric Charges through Various Materials; Production of a Flow of Electric Charges Making a Capacitor Phys104, OBJ, Unit IIB Sp13