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# Ch. 8 DC and AC Circuits

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current   movement of charge between two points that exist at different electrical potentials. movement of positive charge to higher potential (positive) to lower potential (negative)
Kirchhoff's first law   the first law states that the sum of currents directed into a point within a circuit equals the sum of the currents directed away from that point
Kirchhoff's seconds law   the sum of the voltage sources is equal to the sum of the voltage drops around a closed loop circuit
resistance   the opposition to the movement of electrons through a material
conductors   materials that have low resistance
resistors   conductive materials that have moderate resistance
insulators   materials that have very high resistance.
what is resistance related too   the resistivity and is proportional to length of the resistor and inversely proportional to the cross-sectional area of the resistor
ohm's law   for a given resistance, the voltage drop across a resistor is proportional to the magnitude of the current through the resistor
resistors in series   additive to give a resultant resistance that is the sum of all the individual resistances.
resistors in parallel   the magnitude of the current through each circuit division will be inversely proportional to the magnitude of the individual resistances of each circuit division
capacitor   when two electrically neutral metal plates are connected to a voltage source, positive charge builds up on plate connected to positive (higher V) terminal, negative charge builds up on plate connected to negative (lower V) terminal.
when will charge collect on the plates of a capacitor   any time there is a potential difference between the two plates.
capacitance   the ratio of the magnitude of the charge stored on one plate (abs val. of charge) to the total potential difference, voltage, across the capacitor. C=Q/V
SI unit for capacitance   farad. 1F = 1 coulomb/volt
capacitance dependent on geometry   C=e.(A/d) e.=epsilon knot=the permittivity of free space 8.85X10^-12 F/m, A=area of overlap of two plates, d=distance between two plates.
magnitude of electric field between plates   E=V/d. direction will point away from positive plate toward negative plate
potential energy stored in a capacitor   U=1/2CV^2
dielectric material   fancy way of saying insulation. when insulating (air, glass, plastic, ceramics, metal oxides) is placed between charged capacitor, the voltage across the capacitor decreases
what does placing a dielectric between the plates cause   voltage decrease caused by shielding the opposite charges from one another. because they feel each other less, V decreases.
Equation for increase in capacitance due to dielectric effect   C'=KC where K=dielectric constant
what does lowering the voltage between the plates due   makes room for more charge. charge is released from their holding plates either by discharging across the plates of through some conductive material
difference between alternating and direct current   direct current flows in one direction only, while alternating current reverses direction periodically
oscillation equation for AC   i=ImaxSin(2pift)=ImaxSin(wt) i=instantaneous current at time t, Imax=maximum current, f=frequency, w=angular frequency (w=2pif)
RMS current and voltage equations   Irms=(Imax)/(2^(1/2)) Vrms=(Vmax)/(2^(1/2))
equations for power   P=IV, P=I^2R P=V^2/R
resistivity   intrinsic resistance to current flow in a material. resistivity is the proportionality constant that relates a conductor's resistance (R) to the ration of its cross-sectional area (A) to the length of the resistor (L) R=(rhoL)/(A)
resistance and temperature   most conductors have higher R at higher temps. increased thermal oscillation of atoms in conductive material produces a greater resistance to electron flow. temp is intrinsic quality of all matter, so think of resistivity is function of temperature

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