Circuits Flashcards
Current
Flow of positive charge–even though only negative charges are moving
Metallic conductivity
Solid metals & molten forms of some salts
Electrolytic conductivity
conductivity in solutions
Depends on the concentration of the solution
Conductance
Reciprocal of resistance in siemens (S) or siemens/meter (S/m)
Magnitude of current
I=Q/Delta(t)
Which way is current
Direction of the positive charge would flow
DC (direct current)
Charge flows in one direction only
AC (Alternating current)
Current flow changes direction periodically
Electromotive force (emf or e)
when no charge is moving between two terminals of a cell, they are at different potential values (in volts or J/C
Kirchhoff’s Laws
Conservation of charge & energy in a circuit
Kirchhoff’s Junction Rule
At any point or junction in a circuit, the sum of the currents directed into that point equals the sum of currents directed away from that point
Kirchhoff’s Loop Rule
Around any closed circuit loop, the sum of voltage sources will always be equal to the sum of the voltage (potential) drops
Resistance
The opposition within any material to the movement and flow of charge
Resistance equation
R=pL/A
in Ohms
Resistivity
Intrinsic resistance to current flow in material
in Ohm meters
What happens to resistance as temperature increases?
It increases
Ohm’s Law
V=IR
Actual voltage supplied by a cell
V=E(cell) - ir(int
E(cell)= emf of the cell
i=current through cell
rint=internal resistance
What is the internal resistance when there is no current?
0
What is the voltage of a cell when it is open?
=emf
How does the voltage of a cell compare when the current is flowing to when its not?
Less voltage when it is flowing
What kind of cell recharges
Electrolytic
From low to higher potential
What kind of cell discharges
Galvanic (voltaic)
Power of a resistor
Rate at which energy is dissipated by a resistor
Power of a resistor equation
P= IV=I^2R=V^2/R
How are resistances & voltages in series treated?
Additive voltage drops & resistance
How are resistance & voltages in parallel treated?
All voltages are equal
Resistance is reciprocal added
What is the effect of adding resistors in parallel?
Reducing resistance
Capacitator
Hold charge at a particular voltage
Capacitance
Charge (Q)/Potential difference (V)
Parallel plate capacitance
C=eo(A/d)
Uniform electric field equation
E=V/d
What is the direction on capacitor plate?
From positive to negative plate
Potential energy stored in a capacitor
U=1/2CV^2
Dielectric material
Insulation, introduced between capacitator plates & will increase the capacitance by a factor call the dielectric constant (k)
Capacitance due to a dielectric material
C’=kC
Can a dielectric material decrease the capacitance?
No, k is never less than 1
Where does increase in capacitance come from in isolated (no circuit capacitators?
Decrease in voltage
Where does increased capacitance come from in a capacitator in a circuit?
Increase in stored charge on the capacitator
What stays constant in an isolated capacitator?
Charge
What stays constant in a capacitaotr in a circuit?
Voltage
What happens to capacitators in series?
Decrease capacitance
Reciprocal effect
Total voltage=sum of all voltages
What happens to capacitators in parallel?
Addition of all capacitances
Voltages all equal to the source voltage
Anmeter
Used to measure current (low resistance & voltage drop)
Placed in series with the point
Voltmeter
Measure voltage drop across two points, wired in parallel to two points (infinite resistance)
Ohmmeter
Doesn’t require a circuit to be active
Have their own battery of a voltage & finding current to find resistance
Wired in series of two points
How is current calculated with resistors in series?
All currents are equal
How is current calculated with resistors in parallel?
All currents are added
What is the potential difference around a loop?
0 V
Kirchoff’s Loop Rule states that voltage gained by the battery will be used up by the resistors
How to find electromotive force?
Voltage across terminals of battery when no current is flowing
Use V=e-ir(int)
