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Malika Physics MCAT > Circuits > Flashcards

Circuits Flashcards

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1
Q

Ohm’s Law

A

V = IR
V is voltage
I is current
R is resistance

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2
Q

Define resistance

A

A measure of current repulsion, resistance is supplied by resistors (looks like a squiggly line)

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3
Q

Calculating resistance

A

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

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4
Q

How manipulation of wire affects resistance

A
  1. Diameter - as diameter decreases, resistance increases
  2. Temperature - as it increases, resistance increases
  3. Length - as length increases, resistance increases
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5
Q

Define voltage and current

A

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

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6
Q

True or false:
Current moves in the opposite direction as electron flow. It moves from a high potential to low potential.

A

True

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7
Q

Calculating current

A

I = ∆Q/∆t

∆Q is charge
Units: C/s or Amperes (A)

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8
Q

Calculating voltage

A

Vfinal - Vinitial

Units: V or J/C

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9
Q

True or false:
The greater the voltage difference, the greater the resistance.

A

True, voltage difference across a resistor is directly proportional to resistance.

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10
Q

Capacitor

A

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

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11
Q

Capacitance is

A

How much charge can be stored for a given voltage

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12
Q

Potential energy in a capacitor

A

1/2QV or 1/2C*V^2 or Q^2/2C

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13
Q

Calculating capacitance

A

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

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14
Q

True or false:
Area is directly proportional to the capacitance.

A

True.

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15
Q

What does it mean when a capacitor becomes “charged”?
EQUATION to calculate charge of a capacitor

A

The current stops flowing and the Voltage of battery = Voltage of capacitor

Q = Capacitance*voltage of battery

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16
Q

Dielectric definition

A

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

17
Q

Conservation of charge:

A

Total current entering a junction/circuit is equal to the total current exiting the junction/circuit

18
Q

Loop rule

A

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

19
Q

Resistors in series

A

I1 = I2 = I3
*current is the same in series resistors

Vbattery = V1 + V2 + V3

Total resistance (R) = R1 + R2 +R3

20
Q

Resistors in parallel

A

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

21
Q

Capacitor in series

A

(1/Ctotal) = 1/C1 + 1/C2 + 1/C3

22
Q

Capacitor in parallel

A

Ctotal = C1 + C2 + C3

23
Q

Calculating power in a circuit

A

P = IV
P = (I^2)R
P = (V^2)/r

24
Q

Ammeter

A

-Put into a circuit to measure current
-Connects in series
-Needs to have lowest resistance possible

25
Q

Voltmeter

A

-Measures voltage
-Connects in parallel
-Has high resistance

26
Q

Combination circuit problems w/ multiple resistors in series and in parallel

A
  1. Find the smallest possible resistance
    -Here would be the resistance in series = 4
  2. Using the calculated value 4, find the resistance in parallel of the resistors in the smaller circuit = 2
  3. Lastly using the value 2, find the resistance in series of the big resistor and small resistor (2)

Malika Physics MCAT (10 decks)

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