Current and Resistance Flashcards
What is Current? What is the formula that shows Current?
Amount of charge passing through per unit time.
I = Q/dt (A; C/s)
What is the difference between Direct Current and Alternating Current
Direct current is flow in one direction ex. battery and Alternating Current is change direction of flow ex. household
What is Electromotive force(emf)?
Potential difference(V) that tends to give rise to current
What is Junction Rule?
At a junction, the sum of current INTO the path is equal to the sum of current that comes OUT
I(into junction) = I(out junction)
What is Loop Rule?
The sum of all voltages in a closed circuit must be “0”
V(source) = V(drop)
V(lift) = gives positive V
V(resistors) = gives negative V
What is a resistor and its formula?
Resistor is a conductor that allows Voltage drop. R = ρL/A (unit: Ohms) ρ: Resistivity L: Length A: Cross Sectional Area
What is the relationship between Temperature and Resistance?
Proportional
What is Ohm’s Law?
V = IR (unit: V)
I: Current
R: Resistance
What is internal resistance and What is the actual voltage provided in the cell?
r(int) is present in every E(cell)/battery.
V = E(cell) - ir(int)
E(cell) is emf of cell, provides Voltage(+)
ir(int) is the Voltage drop(-)
V = E(cell) - ir(int)
In which direction does the current flow in convention and in reality?
Convention: movement of proton…low to high V(- to +)
Reality: movement of electrons…high to low V(+ to -)
What is Power? Define in terms of Work and Energy
Power is how fast energy is being transferred(energy = work)
P = W/t
P = dE/t
What is Power in terms of Current and Voltage and Resistance?
P = IV P = I^2R P = V^2/R
What is the difference between series and parallel circuit?
Series: connected linearly
Parallel: connected separately, divided
What is the equation for the Voltage drop in Series circuit?
Vs = V1 + V2 + V3…
What is the Equation for the Resistance in Series circuit?
Rs = R1 + R2 + R3…
What is the equation for the Voltage drop in Parallel circuit?
Vp = V1 = V2 = V3…
What is the equation for the Resistance in Parallel circuit?
Rp = 1/R1 + 1/R2 + 1/R3…
What is the difference in terms of Current between Series and Parallel circuits?
Series: Current is the same in each resistor
Parallel: Current might differ depending on R values(As R goes up, I decreases)
How to approach Parallel circuit questions?
1) Get Total Voltage
2) Total Resistance
3) Total Current
What is a Capacitor?
A device that can store charges on the plate
What is the equation for Capacitance in terms of charges? What does it show?
C = Q/V (unit: 1F = 1C/V)
Shows how much charge is present on the plate per voltage
What is the equation for Capacitance in terms of physical geometry of the plates?
C = ε(A/d)
ε: 8.85 x 10^-12 F/m
d: distance between the two plates
A: Cross sectional area of the plates’ overlap
What is the equation for Electric field created by capacitor?
E = V/d
What is the equation for Potential energy stored in a capacitor?
U = 1/2(CV^2)
What are dielectric materials and how do they affect capacitance?
They are insulators and placed between the plates to help increase Capacitance by Capacitors. They prevent charges from flowing and isolate Negative charges(Q-) and Positive charges(Q+) from each other.
What are the two cases of how dielectrics can affect Capacitance by Capacitors?
1) Isolated Capacitor(w/out battery, or taken out later)
…C = Q/V, Increase C by lowering V but Q remains same
2) Circuit Dapacitor(w/ battery)
…C = Q/V, Increase C by increasing Q but V remains same
What is the equation for Capacitance in series?
1/Cs = 1/C1 + 1/C2 + 1/C3… (acts like a big capacitor with large distance “d”)
What is the equation for Capacitance in Parallel?
Cp = C1 + C2 + C3…(acts like a separate capacitor)
What is the equation for the “new” capacitance after a dielectric material has been inserted between capacitor plates?
C' = kC k = dielectric constant
What is the dielectric constant for vacuum?
k = 1.
dielectric materials always increase Capacitance
