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Kaplan Physics > Chapter 8: DC and AC Circuits > Flashcards

Chapter 8: DC and AC Circuits Flashcards

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1
Q

Electrical conductors:

A

materials that allow the free flow of electric charge within them (metals)

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2
Q

Electric current:

A

the flow of charge between two points at different electric potentials connected by a conductor

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3
Q

Equation to determine the total electric current passing through a conductor per unit of time:

A

I = Δq/Δt

where Δq is the amount of charge and Δt is time

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4
Q

The SI unit of current:

A

ampere (1 A = 1 coulomb/second)

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5
Q

The direction of current is:

A

the direction in which positive charge would flow from higher potential to lower potential. The direction of current is opposite the direction of actual electron flow.

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6
Q

The two patterns of current flow:

A

Direct current (DC; flows in one direction) and alternating current (AC; flow changes direction periodically)

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7
Q

Electromotive force:

A

the potential difference (voltage) between two terminals of a cell at different potentials when there is no charge moving; a “pressure to move” that results in current

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8
Q

Kirchoff’s Junction Rule:

A

at any point or junction in a circuit, the sum of the currents directed into that point equals the sum of the currents directed away from that point.

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9
Q

Circuits and currents are governed by:

A

the laws of the conservation of energy; charge and energy can be neither created or destroyed

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10
Q

Kirchoff’s Loop Rule:

A

Around any closed circuit loop, the sum of the voltage sources will always be equal to the sum of voltage (potential) drops.

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11
Q

Resistance is:

A

the opposition to the movement of electrons through a material

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12
Q

Materials with low resistance:

A

conductors

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13
Q

Materials with very high resistance that essentially stop the flow of electrons:

A

insulators

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14
Q

Conductive materials with a moderate amount of resistance, which slows down electrons without stopping them:

A

resistors

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15
Q

Equation to determine the resistance of a given resistor:

A

R = pL/A

where p is the resistivity, R is the resistance, L is the length of the resistor, and A is the cross-sectional area of the resistor

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16
Q

SI unit of resistance:

A

Ohm (Ω)

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17
Q

The longer the length of the resistor:

A

the greater the resistance

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18
Q

The larger the cross-sectional area of a resistor:

A

the less the resistance

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19
Q

The higher the temperature of a resistor:

A

the greater the resistance (due to increased thermal oscillation of the atoms in the conductive material)

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20
Q

The 4 major factors that contribute to resistance:

A

1) resistivity
2) length
3) cross-sectional area
4) temperature

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21
Q

Equation used to determine the drop in electric potential across a resistor:

A

V = iR

where V is the voltage drop, i is the current, and R is the magnitude of resistance

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22
Q

Equation to determine the actual voltage supplied by a cell to a circuit:

A

V = εcell - irint

where i is the current, rint is the internal resistance of the material, and εcell is the emf of the cell

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23
Q

Equation to determine power:

A

P = E/Δt

where E is energy and t is time

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24
Q

Equation to determine the power dissipated by a resistor:

A

P = iV = i2R = V2/R

where i is the current through the resistor, V is the voltage drop across the resistor, and R is the resistance of the resistor

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25
Q

The two ways resistors can be connected in a circuit:

A

in a series or parallel

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26
Q

Voltage drops through a series of resistors are:

A

additive.

Vs = V1 + V2 + V3 + V4 + …

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27
Q

In a circuit with a series of resistors, the current is:

A

the same at every point in the circuit, including through every resistor

28
Q

Equation to determine the total voltage drop across multiple resistors in a series:

A

Vs = V1 + V2 + V3 + V4 + …

29
Q

Equation to determine the resultant resistance of multiple resistors in a series:

A

Rs = R1 + R2 + R3 + R4 + …

30
Q

When resistors are connected in parallel, they are wired with:

A

a common high-potential terminal and a common low-potential terminal

31
Q

Equation to determine the total voltage drop across multiple resistors in parallel:

A

Vp = V1 = V2 = V3 = V4 …

32
Q

Equation to determine the resultant resistance of multiple resistors in parallel:

A

1/Rp = 1/R1 + 1/R2 + 1/R3 + …

33
Q

When n identical resistors are wired in parallel, the total resistance is given by the equation:

A

R/n

34
Q

When approaching circuit problems, the first three things you need to find are:

A

1) total voltage
2) total resistance
3) total current

35
Q

Ohm’s law states that:

A

for a given resistance, the magnitude of the current through a resistor is proportional to the voltage drop across the resistor

36
Q

Across each resistor in a circuit, a certain amount of ___ is dissipated.

A

power

37
Q

The amount of power dissipated by a resistor in a circuit is dependent on:

A

the current through the resistor and the voltage drop across the resistor

38
Q

Resistors in series are:

A

additive and sum together to create the total resistance of the circuit

39
Q

Resistors in parallel:

A

cause a decrease in resultant resistance of a circuit

40
Q

Equation to determine the capacitance of a capacitor:

A

C = Q/V

where Q is the absolute value of the charge and V is the voltage applied

41
Q

SI unit of capacitance:

A

farad

(1F = 1 coulomb/volt)

42
Q

microfarads (uF) =

A

1 X 10-6 F

43
Q

picofarads (pF) =

A

1 X 10-12F

44
Q

Equation to determine the capacitance of a parallel plate capacitor:

A

C = εo (A/d)

where εo is 8.85 X 10-12, A is the area of overlap of the two plates, and d is the separation of the two plates

45
Q

Equation to determine the electric field at a point in space between the plates of a parallel plate capacitor:

A

E = V/d

where V is the volatage applied across the plates and d is the separation between the plates

46
Q

The direction of the electric field at any point between parallel plate capacitors is:

A

away from the positive plate and toward the negative plate

47
Q

Equation to determine the potential energy stored in a capacitor:

A

U = 1/2CV2

where C is the capacitance of the capacitor and V is the voltage applied

48
Q

A dielectric material is:

A

an insulator placed between the plates of a capacitor that increases the capacitance of the capacitor by a factor equal to the material’s dielectric constant, K

49
Q

Dielectric constant (K) is:

A

a measure of the insulating capability of a particular dielectric material

50
Q

Equation used to determine the increase in capacitance due to a dielectric material:

A

C’ = KC

where C’ is the new capacitance and C is the original capacitance

51
Q

Capacitance of capacitors in series behave in the same manner as:

A

resistors in parallel

52
Q

Equation to determine the total voltage across multiple capacitors in series:

A

Vs = V1 + V2 + V3 + V4 + …

53
Q

Equation to determine the resultant capacitance across multiple capacitors in series:

A

1/Cs = 1/C1 + 1/C2 + 1/C3 + ..

54
Q

Adding resistors in parallel ___ overall resistance:

A

decreases

55
Q

Adding capacitors in parallel ___ overall capacitance:

A

increases

56
Q

Equation to determine the total voltage across multiple capacitors in parallel:

A

Vp = V1 = V2 = V3 = V4 + …

57
Q

Equation to determine the resultant capacitance across multiple capacitors in parallel:

A

Cp = C1 + C2 + C3 + C4 + …

58
Q

In series, what happens to the capacitance as more capacitors are added?

A

it decreases

59
Q

In parallel, what happens to the capacitance as more capacitors are added?

A

it increases

60
Q

The equations for voltage, resistance, and capacitance in series:

A

Vs = V1 + V2 + V3 …

Rs = R1 + R2 + R3 …

1/Cs = 1/C1 + 1/C2 + 1/C3

61
Q

The equations for voltage, resistance, and capacitance in parallel:

A

Vp = V1 = V2 = V3 …

1/Rp = 1/R1 + 1/R2 + 1/R3 …

Cp = C1 + C2 + C3 + …

62
Q

Alternating current oscillates in what manner?

A

sinusoidal, from +imax to -imax

63
Q

Equation to estimate the average magnitude of alternating current over time:

A

irms = imax / √2

where imax is the maximum current and irms is the average current

64
Q

Capacitors have the ability to:

A

store electric charge and discharge the energy later

65
Q

Equation to estimate the average magnitude of AC voltage over one period:

A

Vrms = Vmax / √2

where Vmax is the maximum voltage and Vrms is the average voltage

66
Q

Once you have calculated the Irms and Vrms values for alternating current, what can you plug these values into?

A

Ohm’s law

67
Q

Equation for the instantaneous current of an alternating current:

A

i = imaxsin(2πft) = imaxsin(ωt)

where i is the instantaneous current, imax is the maximum current, f is the frequency, and ω is the angular frequency

Kaplan Physics (14 decks)

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