Ch 2: Basic Components and Electric Circuits

Question 1

Kirchhoff’s Voltage Law

Answer 1

The sum of the voltages across each element of a loop/mesh is zero.

Σ V_n = 0

Question 2

Kirchhoff’s Current Law

Answer 2

The sum of all currents entering and exiting a given node is 0.

Σ i_n = 0

Question 3

Ohm’s Law

Answer 3

V = IR

The voltage across an element is the product of the current through the element and the resistance of the element.

Question 4

Current:

Definition

Mathematical Relation to Charge

Unit

Answer 4

Current is the charge moved through an element, per unit time.

i = dq/dt

Unit: Ampere(A) = 1 coulomb/second

Question 5

Sum of Power in a circuit

Answer 5

The sum of absorbed power for each element is zero.

The sum of the absorbed power equals the sum of the supplied power.

All power that goes into a circuit must be absorbed by the circuit elements.

Σp_absorbed = Σp_supplied

Question 6

Definition of Network

Answer 6

Interconnection of two or more simple circuit elements

Question 7

Definition of

Circuit

Answer 7

A network with at least one closed path

Question 8

Circuit Diagrams:

Element Polarity:

Passive Elements

vs

Voltage Source

Answer 8

For Passive Elements:

The terminal receiving positive current is labeled with a ( + )

The other terminal is negative ( - )

For a Voltage Source,

The terminal supplying positive current is +, the other is negative, -

Question 9

Independent Current Source

Answer 9

An ideal element in which the current through the element is constant,

independent of the voltage across it.

This is accomplished with active elements beyond the scope of analyzing the circuit in question.

Question 10

SI Unit of Resistance

Answer 10

Ohm - Ω

1 Ω = 1 V/A

Question 11

Power, Voltage and Current relationship

Answer 11

Power is the product of current and voltage

p = iv

or

P = IV

Question 12

Passive Sign Convention

Answer 12

Determines how power absorbed/supplied by element within the circuit is represented.

When an element ABSORBS power, the terminal that current flows into is positive. Power is treated as “positive” (+p)

When an element GENERATES power, the terminal that current flows OUT OF is positive.

Power is treated as “negative”.

(-p)

Question 13

Dependent Sources

Answer 13

Voltage or Current Sources whose source quantity is controlled by a voltage or current somewhere else in the circuit.

These sources are represented with diamonds instead of circles.

Question 14

Active Elements

vs

Passive Elements

Answer 14

Active Element

An element capable of furnishing an average power greater than zero to some external device, over an infinite time interval.

Usually voltage or current sources.

Passive Element

An element that cannot supply an average power greater than zero over an infinite time interval.

Question 15

Conductance:

Definition

Relation to voltage

Units

Answer 15

Conductance (G) is the inverse of resistance. It is the amount of current that passes through an element, per unit of voltage.

The ratio of current to voltage.

G = i/v = 1/R

Unit: Siemens (S) in SI

an older unit is the “mho”, represented by the inverted omega symbol, or Ω^-1

Question 16

Independent Voltage Source

Answer 16

An ideal element that has a constant terminal voltage, independent of the current through it.

Represented by a circular element (independent) with Plus and minus signs at the appropriate terminals.

Question 17

SI Unit

of Work or Energy

Answer 17

The Joule (J)

1 J = 1 kg*m² / s²

Question 18

SI Unit

of Power

Answer 18

Watt (W)

Work/Energy over time

1 W = 1 J/s

Question 19

Linear Dependent Source

Answer 19

A dependent current or voltage source,

whose output current or voltage is proportional only to the first power of a specified current or voltage variable in the circuit.

Typically related by a value “k”

Question 20

SI:

Base Units and Symbols (7)

Answer 20

Base Quantity

Name

Symbol

length

meter

m

mass

kilogram

kg

time

second

s

electric current

ampere

A

Temperature

Kelvin

K

Amount of Substance

mole

mol

Luminous Intensity

candela

cd

Question 21

Relationship

between

Current and Charge

Answer 21

Current is the rate of charge moved through an element

i = dq/dt

or

q(t) = ∫i dt + q(t₀)

Question 22

SI Unit of

Voltage

Answer 22

Volt ( V )

1 V = 1 Joule/Coulomb

Question 23

SI Unit of

Charge

Answer 23

Coulomb (C)

The total charge that passes through a cross section of wire in 1 second at 1 ampere of current

Static Representation: Q

Instantaneous Amount: q(t) or q

Question 24

Voltage Division

Answer 24

Place two resistors in series. the voltage across each resistor can be calculated simply, proportionally to voltage across both. The voltage is “divided” between the two resistors

V₁ = V * R₁/(R₁ + R₂)

V₂ = V * R₂/(R₁ + R₂)

Question 25

Current Division

Answer 25

Similar in concept to voltage division.

Resistors are placed in parallel, effectively dividing the total current into the current through each resistor.

i₁ = i * R₁/(R₁ + R₂)

i₂ = i * R₂/(R₁ + R₂)

Question 26

What is Voltage?

Answer 26

Voltage is a difference in charge between two points.

Equal to the energy required to move a unit of charge between two places.

Question 27

Charge of

a single Electron

Answer 27

-1.602 x 10^-19 Coulombs

Question 28

Power

Definition

Equation

Units

Answer 28

Power is the rate of energy provided or consumed per unit time.

Equation: p = vi

Units: Watts (W)

Question 29

Three Characteristics

of an

Ideal Circuit

Answer 29

• Electrical Effects propagate instantly through the whole system (assuming a lumped system)
• Net charge of every component in the system is ZERO. (Charge in = Charge out)
• No magnetic Couplings

Question 30

Current, Voltage, Power

Properties of an Ideal Circuit

Answer 30

• Current measured on various parts of a connecting line are the same
• Voltage across 2 terminals is the same, regardless of which side of the terminal the measurement is made
• Sum of element powers in a circuit equals zero.
  
  • Generated Power = Absorbed Power

Question 31

Ideal Basic Circuit Element:

Three Attributes

Answer 31

• Only has two terminals which are the points it connects to other elements
• It can be fully described in terms of relationship between current and voltage
• It cannot be subdivided into other elements