DC and AC Circuits

Question 1

Conductor

Answer 1

Material where electrons move easily

Question 2

Insulator

Answer 2

Material where electrons do not move easily

Question 3

Direct Current

Answer 3

Current that flows in one direction only

Question 4

Alternating Current

Answer 4

Current that flows in two directions that change periodically

Question 5

In which direction does current flow?

Answer 5

From the positive part of the battery to the negative part

Question 6

Electromotive Force

Answer 6

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

Question 7

Resistance

Answer 7

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

Question 8

What increases the resistance of a conductor?

Answer 8

• 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)

Question 9

Resistivity

Answer 9

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

Question 10

Ohm’s Law

Answer 10

V = IR

Question 11

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

Answer 11

This is equal to the power dissipated by the resistor:

P = iV = i^2 R = V^2/ R

Question 12

Electric Circuit

Answer 12

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

Question 13

Kirchhoff’s Laws

Answer 13

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

Question 14

What happens when resistors are placed in series?

Answer 14

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.

Question 15

What happens when resistors are placed in parallel?

Answer 15

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.

Question 16

Capacitor

Answer 16

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

Question 17

Capacitance

Answer 17

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

Question 18

Permittivity of Free Space

Answer 18

ε0 = 8.85 X 10^-12 F/ m

Question 19

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

Answer 19

E = V/ d

The electric field points toward the negative plate and away from the positive plate.

Question 20

Dielectric

Answer 20

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

Question 21

Dielectric Constant

Answer 21

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

Question 22

What happens when capacitors are placed in parallel?

Answer 22

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.

Question 23

What happens when capacitors are added in series?

Answer 23

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.

Question 24

Electron Volt

Answer 24

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

Question 25

What is the most common form of AC current oscillation?

Answer 25

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

Question 26

Current for sinusoidal waves

Answer 26

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

Question 27

What is the average value of an AC current?

Answer 27

0

Question 28

What is the average power in an AC circuit?

Answer 28

Not 0, because P = i^2 R

Question 29

RMS Current

Answer 29

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

Question 30

RMS Voltage

Answer 30

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