Concepts for Unit 11
- resistance is a property of a circuit element due to the resistivity of the material and the geometry of the circuit element
- resistance corresponds to the tendency of an object to dissipate electrical energy when charge carriers pass through it
- capacitance is a property of a circuit element due to its geometry and the dielectric constant of the material that separates the plates of the capacitor
- capacitance is related to the ability of the circuit element to store electrical potential energy via polarization of the device
- mobile charge is present in all conductors, whether a current is present or not
- current is a net movement of charge; individual charge carriers continue to move in random directions but overall, the collection of charge carriers moves in a direction around a circuit
- current is not the speed of the charge carriers moving, but the number of charge carriers moving through a cross-sectional area with respect to time
- the current is the same everywhere in the circuit, even though the cross-sectional areas and the speed of the charge carriers may be different
- a battery is a source of potential difference (and therefore electrical potential energy) in a circuit, not a source of charge
- positive charge moves from high potential to low potential
- an electric field is present in a conductor in a circuit when there is a potential difference (contrary to when charge is static)
- when a switch is closed in a circuit, all of the charge begins moving at essentially the same time
- devices/loads in a circuit transfer electrical energy out of the circuit
- brightness of a bulb in a circuit is most closely related to the electrical power the bulb dissipates
- the behavior of a capacitor is related to the amount of charge present on the capacitor plates at any instant of time
- in charging a capacitor, an initially uncharged capacitor offers no resistance to the movement of charge carriers for an instant; no charge carriers move onto or off of the capacitor when it is fully charged
- when a capacitor in a circuit is fully charged, the potential difference across it due to the charge stored on it is equal and opposite to the external potential difference applied across the capacitor
- in discharging a capacitor, the current is a maximum when the circuit is first completed and decreases with respect to time
- RC circuits behave in predictable ways; after four time constants practically all of the change (either charging or discharging) has happened
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