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Unformatted text preview: rostatic equilibrium is an equipotential surface • Because the electric field is zero inside the conductor, we conclude that the electric potential is constant everywhere inside the conductor and equal to the value at the surface E Compared to V
• The electric potential is a function of r • The electric field is a function of r2 • The effect of a charge on the space surrounding it
– The charge sets up a vector electric field which is related to the force – The charge sets up a scalar potential which is related to the energy Definition of Capacitance
• Capacitors are devices that store electric charge • The capacitance, C, of a capacitor is defined as the ratio of the magnitude of the charge on either conductor to the potential difference between the conductors • The SI unit of capacitance is a farad (F) Makeup of a Capacitor
• A capacitor consists of two conductors
– When the conductors are charged, they carry charges of equal magnitude and opposite directions • A potential difference exists between the conductors due to the charge Field Due to a Plane of Charge (Ch19)
• The total charge in the surface is A • Applying Gauss’ Law • Note, this does not depend on r • Therefore, the field is uniform everywhere Parallel Plate Capacitor
• Each plate is connected to a terminal of the battery • If the capacitor is initially uncharged, the battery establishes an electric field in the connecting wires •The charge density on the plates is Capacitance Parallel Plate Assumptions • The assumption that the electric field is uniform is valid in the central region, but not at the ends of the plates • If the separation between the plates is small compared with the length of the plates, the effect of the non-uniform field can be ignored Energy in a Capacitor – Overview
• Consider the circuit to be a system • Before the switch is close...
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- Winter '10