Circuits Flashcards
Ohm’s Law
V = IR
V is voltage
I is current
R is resistance
Define resistance
A measure of current repulsion, resistance is supplied by resistors (looks like a squiggly line)
Calculating resistance
R = (resistivity*Length)/Area
L is length of the resistor.
Resistivity is an intrinsic value dependent on material used.
*Insulators have higher resistivity than conductors
Units: Ohms
How manipulation of wire affects resistance
- Diameter - as diameter decreases, resistance increases
- Temperature - as it increases, resistance increases
- Length - as length increases, resistance increases
Define voltage and current
Voltage - the difference in electric potential between two points that drives the movement of electric charges
Current - the net movement of electric charges, it is constant w/ the same amount entering & exiting the resistor
True or false:
Current moves in the opposite direction as electron flow. It moves from a high potential to low potential.
True
Calculating current
I = ∆Q/∆t
∆Q is charge
Units: C/s or Amperes (A)
Calculating voltage
Vfinal - Vinitial
Units: V or J/C
True or false:
The greater the voltage difference, the greater the resistance.
True, voltage difference across a resistor is directly proportional to resistance.
Capacitor
2 parallel conducting plates separated by a vacuum or insulating material called a dielectric
-They store a charge for a given voltage (potential difference)
-Serves same function as a battery
Capacitance is
How much charge can be stored for a given voltage
Potential energy in a capacitor
1/2QV or 1/2C*V^2 or Q^2/2C
Calculating capacitance
C = (Kε0A)/d
K is the dielectric constant
ε0 is the permittivity of free space constant
A is the area of 1 conducting plate
d is distance between the plates
True or false:
Area is directly proportional to the capacitance.
True.
What does it mean when a capacitor becomes “charged”?
EQUATION to calculate charge of a capacitor
The current stops flowing and the Voltage of battery = Voltage of capacitor
Q = Capacitance*voltage of battery
Dielectric definition
An insulating material that is polarizable which is added in between parallel plates to increase capacitance
It reduces the total E between the capacitor plates which reduces the voltage between the plates
Conservation of charge:
Total current entering a junction/circuit is equal to the total current exiting the junction/circuit
Loop rule
The sum of the voltages around any closed loop is 0
Vbattery - V1 - V2 = 0
Voltage starts from the battery as it goes around the circuit, it enters the 1st resistor and drops in V, then enters the second resistor and drops more until it becomes 0
Resistors in series
I1 = I2 = I3
*current is the same in series resistors
Vbattery = V1 + V2 + V3
Total resistance (R) = R1 + R2 +R3
Resistors in parallel
Itotal = I1 + I2 + I3
Vbattery = V1 = V2 = V3
*Voltage is the same in parallel resistors
(1/Rtotal) = (1/R1) + (1/R2) + (1/R3)
*Total resistance is lower in parallel setup
Capacitor in series
(1/Ctotal) = 1/C1 + 1/C2 + 1/C3
Capacitor in parallel
Ctotal = C1 + C2 + C3
Calculating power in a circuit
P = IV
P = (I^2)R
P = (V^2)/r
Ammeter
-Put into a circuit to measure current
-Connects in series
-Needs to have lowest resistance possible
Voltmeter
-Measures voltage
-Connects in parallel
-Has high resistance
Combination circuit problems w/ multiple resistors in series and in parallel
- Find the smallest possible resistance
-Here would be the resistance in series = 4 - Using the calculated value 4, find the resistance in parallel of the resistors in the smaller circuit = 2
- Lastly using the value 2, find the resistance in series of the big resistor and small resistor (2)
