1 PHYS122 Exam 2 Topics Electricity A. Electrostatics 1. Charge, field and potential a. Properties of electric charge b. Coulomb's Law c. Electric field d. Electric potential energy e. Electric potential 2. Conductors, capacitors, dielectrics a. Potentials and charged surfaces b. Parallel plate capacitors B. Electric currents 1. Current and resistance a. Current b. Ohm's law c. Electric power 2. Direct current circuits a. Sources of emf b. Resistors in series and parallel c. Kirchoff's rules d. RC circuits Objectives A. Electrostatics 1. Charge, Field and potential a. Understand the concept of electric field so you can: 1). Define it in terms of the force on a test charge. 2). Calculate the magnitude and direction of the force on a positive or negative charge placed in a specified field. 3). Calculate the net force on a collection of charges in an electric field. 4). Given a diagram on which an electric field is represented by flux lines, determine the direction of the field at a given point, identify locations where the field is strong and where it is weak, and identify where positive and negative charges must be present. 5). Analyze the motion of a particle of specified charge and mass in a uniform electric field. b. Understand the concept of electric potential so you can: 1). Calculate the electrical work done on a positive or negative charge that moves through a specified potential difference. 2). Given a sketch of equipotentials for a charge configuration, determine the direction and approximate magnitude of the electric field at various positions. 3). Apply conservation of energy to determine the speed of a charged particle that has been accelerated through a specified potential difference. 4). Calculate the potential difference between two points in a uniform electric field, and state which is at the higher potential.2 2. Coulomb's law and field and potential of point charges a. Understand Coulomb's law and the principle of superposition so you can: 1). Determine the force that acts between specified point charges, and describe the electric field of a single point charge. 2). Use vector addition to determine the electric field produced by two or more point charges. b. Know the potential function for a point charge so you can determine the electric potential in the vicinity of one or more point charges. B. Conductors, capacitors, dielectrics 1. Electrostatics with conductors a. Understand the nature of electric fields in and around conductors so you can: 1). Explain the mechanics responsible for the absence of electric field inside a conductor, and why all excess charge must reside on the surface of the conductor. 2). Explain why a conductor must be an equipotential, and apply this principle in analyzing what happens when conductors are joined by wires. 3). Determine the direction of the force on a charged particle brought near an uncharged or grounded conductor. b. Be able to describe and sketch a graph of the electric field and potential inside and outside a charged conducting sphere. c. Understand induced charge and electrostatic shielding so you can describe qualitatively the process of charging by induction. 2. Capacitors and dielectrics a. Know the definition of capacitance so you can relate stored charge and voltage for a capacitor. b. Understand energy storage in capacitors so you can: 1). Relate voltage, charge, and stored energy for a capacitor. 2). Recognize situations in which energy stored in a capacitor is converted to other forms. c. understand the physics of the parallel-plate capacitor so you can: 1). Describe the electric field inside the capacitor, and relate the strength of this field to the potential difference between the plates and the plate separation. 2). Determine how changes in dimension will affect the value of the capacitance. C. Electric currents 1. Current, resistance, power a. understand the definition of electric current so you can relate the magnitude and direction of the current in the wire or ionized medium to the rate of flow of positive and negative charge. b. understand conductivity, resistivity, and resistance so you can: 1). Relate current and voltage for a resistor. 2). Describe how the resistance of a resistor depends upon its length and cross-sectional area. 3). Apply the relations for the rate of heat production in a resistor.3 2. Steady-state direct currents with batteries and resistors only. a. Understand the behavior series and parallel combinations of resistors so you can: 1). Identify on a circuit diagram resistors that are in series or in parallel. 2). Determine the ratio of the voltages across resistors connected in series or the ratio of the currents through resistors connected in parallel. 3). Calculate the equivalent resistance of two or more resistors connected in series or connected in parallel, or of a network of resistors that can be broken down into series and parallel combinations. 4). Calculate the voltage, current, and power dissipation for any resistor in such a network of resistors connected to a single battery. 5). Design a simple series-parallel circuit that produces a given current and terminal voltage for one specified component, and draw a diagram for the circuit using conventional symbols. b. Be able to apply Ohm's law and Kirchoff's rules to direct-current circuits in order to determine a single unknown current, voltage, or resistance. 3. Capacitors in circuits a. Understand the behavior of capacitors connected in series or parallel so you can: 1). Calculate the equivalent capacitance of a series or parallel combination. 2). Describe how stored charge is divided between two capacitors connected in parallel. 3). Determine the ratio of voltages for two capacitors connected in series. b. Be able to calculate the voltage or stored charge, under steady-state conditions, for a capacitor connected to a circuit consisting of a battery and resistors. c. Develop skill in analyzing the behavior of circuits containing several capacitors and resistors so you can determine voltages and currents immediately after a switch has been closed and also after steady-state conditions have been established.4 Equations 122EKq qFr= 29201Nm8.99 104CKπε==×271.67 10 kgpm−=× onqFEq→= 2014qErπε= 0QEAε= 191.6 10 Ce−=× 319.11 10 kgem−=× 21202C8.85 10Nmε−=× EUqV= 12 12014Eqq qqUKrrπε== 014qqVKrrπε== VEdΔ= QCV=Δ 0ACdκε= ()221122CQUCVC==Δ
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