DC and AC Circuits Flashcards Preview

MCAT Physical Sciences > DC and AC Circuits > Flashcards

Flashcards in DC and AC Circuits Deck (30):
1

Conductor

Material where electrons move easily

2

Insulator

Material where electrons do not move easily

3

Direct Current

Current that flows in one direction only

4

Alternating Current

Current that flows in two directions that change periodically

5

In which direction does current flow?

From the positive part of the battery to the negative part

6

Electromotive Force

The voltage across the terminals of a cell when there is no current.
V = emf - i r(internal)

7

Resistance

R = i/ V
Units: Ohm
Current does not change due to resistance, because no charge is lost.

8

What increases the resistance of a conductor?

- Increased wire length because the current travels a longer path
- Decreases cross-sectional area because there are fewer conduction paths for electrons to follow
- Increased resistivity
- Increased temperature because of the increased thermal oscillations of the atoms (except for glass, pure silicon, and most semiconductors)

9

Resistivity

Intrinsic resistance property of a conductor that is independent of length and cross-sectional area
R = ρ L/ A
ρ has units of ohm meter

10

Ohm's Law

V = IR

11

What is the rate at which electric energy converts to heat?

This is equal to the power dissipated by the resistor:
P = iV = i^2 R = V^2/ R

12

Electric Circuit

Conducting pathway that has one or more voltage sources connected to passive circuit elements

13

Kirchhoff's Laws

1) The sum of currents directed into a junction equals the sum of currents directed away from the junction following from the conservation of electric charge
2) Voltage source sum equals voltage drop sum in a circuit loop, because energy is conserved in a complete circuit loop where energy is gained back in the battery

14

What happens when resistors are placed in series?

Each resistor in series increases total resistance while decreasing total current. Sum up each of the individual resistances to create an equivalent resistor for calculations. The voltage drops may differ for each resistor in series, but the sum of the voltage drops will equal the sum of voltage sources.

15

What happens when resistors are placed in parallel?

Each resistor in parallel decreases the total resistance and increases the current that can flow. The reciprocal of equivalent resistance equals the sum of the reciprocals of individual resistances. The voltage drop across each is the same and equal to the voltage drop across the combination. R/n when there are multiple resistors of the same resistance placed in parallel.

16

Capacitor

Two conducting plates separated a short distance by a dielectric. Capacitors store electrical charge.

17

Capacitance

C = Q/ V
Units: Farad = C/ V
It is dependent on the conducting surface geometry
Parallel Plate Capacitor: C = ε0 A/d

18

Permittivity of Free Space

ε0 = 8.85 X 10^-12 F/ m

19

Electric Field between the plats of a parallel plate capacitor in a uniform field

E = V/ d
The electric field points toward the negative plate and away from the positive plate.

20

Dielectric

Insulating material between the plats of a capacitor that lowers the voltage across a charged-up capacitor, increasing the capacitance.

21

Dielectric Constant

Dimensionless number that describes how the capacitance changes with a dielectric
C' = KC

22

What happens when capacitors are placed in parallel?

The total capacitance increases with each capacitor added. Sum up each individual capacitance to determine the equivalent capacitance. The voltage across each parallel capacitor is equal to the voltage across the entire combination.

23

What happens when capacitors are added in series?

The total capacitance decreases with each capacitor added in series. The reciprocal of the equivalent capacitance is equal to the sum of the reciprocals of all of the individual capacitances in series. The sum of the voltage drops across each capacitor in series is equal to the sum of the source voltages.

24

Electron Volt

The voltage created by the potential difference between two terminal of a cell when no current flows
1 eV = 1.60 X 10^-19 J

25

What is the most common form of AC current oscillation?

Sinusoidal, where current flows on direction for half the cycle and the other direction for the other half of the cycle.

26

Current for sinusoidal waves

i = I(max) sin (2π ft) = I(max) sin ωt

27

What is the average value of an AC current?

0

28

What is the average power in an AC circuit?

Not 0, because P = i^2 R

29

RMS Current

I(rms) = I(max)/ 2^1/2

30

RMS Voltage

V(rms) = V(max)/ 2^1/2