6. Circuits Flashcards
Capacitance (C) formula. Definition of capacitance and factors affecting it
C = Q/deltaVoltage in Farads; Q = charge in C
Storage of charge per unit voltage. Made up of 2 parallel conducting plates separated by insulating material or vacuum. IF YOU WANT TO CHARGE SOMETHING FAST, DEC THE CAPACITANCE SINCE IT’S STORING CHARGE
Capacitance = directly proportional to area and inversely proportional to distance: C = epsilon_0*(A/d) where epsilon_0=permittivity of free space, A=area of overlap b/w 2 plates, and d=separation of 2 plates
Voltage (V) formula aka Ohm’s Law
V = IR
Current (I) formula. What’s the direction of current?
charge over time = Q/t, units: Amperes
Direction a pos charge would flow: high to low potential (ie. Based on flow of e- moving from low potential to high potential, so technically direction of current flows opposite to flow of e-); current by definition = moving charge in space
How to add up resistors in a series circuit? In a parallel circuit?
Rtotal = R1 + R2 + R3... etc for series 1/Rtotal = 1/R1 + 1/R2 + 1/R3... etc for parallel
In a series circuit, what happens to values of V, I and R?
V: voltage = diff for each resistor
I: current = constant throughout entire circuit
R: resistance can be diff
In a parallel circuit, what happens to values of V, I and R?
V: voltage = same for each resistor
I: current = diff when splitting into parallel circuits but are additive
R: resistance can be diff
How to add up capacitors in a series circuit? In a parallel circuit?
1/Ctotal = 1/C1 + 1/C2 + 1/C3... etc for series Ctotal = C1 + C2 + C3... etc for parallel
In a series circuit, what happens to values of V, Q and C?
V: voltage = diff for each capacitor but is additive
Q: charge = same for all capacitors throughout circuit –> find Ceq to find charge
C: capacitance can be diff
In a parallel circuit, what happens to values of V, Q and C?
V: voltage = same for all capacitors throughout circuit
Q: charge = diff for each capacitor but is additive to Ceq charge
C: capacitance can be diff
Definition of resistance, formula, and factors affecting it
Opposition to flow of charge. R = (rho*L)/A
Length = directly proportional to resistance: double the length of resistor —> double the resistance
Cross-sectional area = inversely proportional to resistance: double the cross-sectional area —> half the resistance (cuz inc area means more pathways thru resistor => conduction pathways); thicker wire => bigger cross sectional area; A IS NOT SURFACE AREA
Higher temp —> greater resistance
Adding a resistor to a capacitor would dec V in series and keep V constant in parallel
Power is dissipated by resistors. What’s the formula relating to power and resistance?
P = I^2*R and you can rearrange it to P = IV and P = V^2/R; it’s the rate of electrical energy transferred
Potential energy stored by capacitors formula
U = 1/2CV^2 and you can rearrange it
Kirchhoff’s junction rule vs loop rule
Current vs voltage in is the same going out (additive)
Direct vs alternative current
Charge flows in 1 direction only vs charge flow changes direction periodically
Dielectric material and dielectric constant
Another way to say insulator —> stores more charge for capacitor by a factor of the constant. Higher dielectric constant —> higher insulation —> inc capacitance —> stores more charge. The constant will NEVER be less than 1 b/c dielectric materials will NEVER dec capacitance. It’s polarizeable b/c its molec have dipoles that can be oriented in particular directions
Dielectrics in isolated vs circuit capacitors
If dielectric material = placed in capacitor NOT connected to a circuit —> voltage across capacitor dec —> capacitance inc vs if dielectric material = placed in capacitor connected to a circuit —> voltage stays the same in order to equal the voltage drop (remember Kirchoff’s Law); capacitance still inc
How to find new capacitance after dielectric material is introduced?
C’ = k*C
k=dielectric constant
Ammeter vs voltmeter vs ohmmeter
Meters that measure current in active series circuit, they have negligible resistance vs meters that measure voltage drop across 2 points in active parallel circuit, they have high resistance vs measures current in a circuit like ammeter (doesn’t matter if circuit is on or off) and uses own voltage (they’re self powered) to do Ohm’s law to find resistance, have negligible resistance
Formula to find uniform electric field in capacitor
E = V/d, direction of electric field = always from pos plate to neg plate
How to find voltage using emf
V = Ecell - IRint, where Ecell = also emf and Rint = internal resistance
What type of energy is carried by battery vs current vs resistor?
chemical vs electrical vs thermal
