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Chapter 24
Capacitance, Dielectrics, Energy Storage
Introduction: Our approach
• Getting familiar with capacitors
• Defining and calculating capacitance
• Understanding what happens when capacitors are in a circuit
• Understanding energy in a capacitor
• Understanding the role of dielectrics in capacitors
Capacitors
• What are the main uses of devices called capacitors?
• How does a capacitor “store charge” without having a net charge?
• How are capacitors constructed?
• In what sense can just about any object be considered a capacitor?
Capacitance
• What is the definition of capacitance?
• In general, how can capacitance be calculated from the electric field?
• How is capacitance calculated for a few simple capacitors?
Connected Capacitors
• What is meant by a (closed) electrical circuit?
• How are capacitors in circuits represented diagrammatically?
• What is meant by two or more capacitors in series?
• What is meant by two or more capacitors in parallel?
Connected Capacitors (cont’d.)
• What is the equivalent capacitance for capacitors in series?
• What is the equivalent capacitance for capacitors in parallel?
• How is the distribution of charge determined when capacitors, some of which were initially charged, are connected in a circuit?
Energy in capacitors
• How is the energy in a capacitor defined?
• What is the energy in a capacitor in terms of the capacitance, charge, and voltage of the capacitor?
• How does the energy of a capacitor change as its separation increases? How does it matter whether the capacitor is connected to a battery?
Energy in capacitors (cont’d)
• Where is the energy in a capacitor?
• In the above framework, how is the quantity of energy defined and expressed in terms of other quantities?
Dielectrics
• What is a dielectric? What are some examples?
• How is the dielectric constant defined?
• Why is it reasonable that a capacitor with a dielectric in the spacing has a greater capacitance?
• What is dielectric strength?
• What is the permittivity of a material?
Dielectrics (microscopically)
• What is going on microscopically when a dielectric is in a capacitor?
• What is referred to by E0, Eind, σind, Qind, free charge, bound charge, K?
the end
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