Question 


Answer 


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 crosssectional 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 crosssectional 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 
