Electric Circuits - Exam Review

Flashcards for reviewing key concepts and formulas from the Electric Circuits textbook.

What unit system is used in the book?

The International System of Units (SI) is used throughout the book.

What does Table 1-2 list?

The electrical quantities and their symbols commonly used in electrical circuit analysis.

What are the two supplementary quantities and their SI units?

Plane angle (radian) and solid angle (steradian).

What is the defining equation for the newton (N)?

Force equals mass times acceleration.

What is a useful concept about current?

Current results from charges in motion, and 1 ampere is equivalent to 1 coulomb of charge moving across a fixed surface in 1 second.

What is of interest when an electric charge experiences a force in an electric field?

The work done to move the charge against the electric field.

What does the product of voltage and current yield?

Electric power in watts, where p=vi.

What is the difference between passive and active elements?

Active elements supply energy to the network; passive elements take energy from the sources.

What are Independent sources?

Voltage or current sources that are not affected by changes in the connected circuit.

What is the sign convention for passive circuit elements R, L, and C?

The terminal where the current enters is generally treated as positive with respect to the terminal where the current leaves.

In the dc circuit, if the current enters VA at the negative terminal, what does this mean?

VA provides power, while the resistor and VB absorb power.

What are the passive circuit elements?

Resistance R, inductance L, and capacitance C.

What is the function of the circuit elements resistance R, inductance L, and capacitance C?

A resistor always consumes energy; inductors and capacitors store energy and return it.

How is energy determined as the integral of the instantaneous power?

w = ∫ pdt = ∫ i^2R dt = ∫ υ^2/R dt

What ist the Energy stored in the magnetic field of an inductance?

w = (1/2)Li^2. The energy is zero at t = 0 and t = (p /50) s.

What results in stored energy in a capacitor?

q = Cu. Charge, q on a capacitor results in an electric field in the dielectric which is the mechanism of the energy storage

What does the solution generally answer?

The solution answers questions about the operation of the device under conditions applied by a source of energy.

What does Kirchhoff's voltage law (KVL) state?

The algebraic sum of the voltages is zero.

What is conservation of electric charge?

The Basis for Kirchhoff's current law (KCL).

In Circuit element in Series with Resistors what is the current?

i =u/Req

In Circuit element in Parallel with Resistors, what is the voltage?

u = iReq

In a two-branch current divider, what does that mean?

The ratio of the current in one branch of a two-branch parallel circuit to the total current is equal to the ratio of the resistance of the other branch resistance to the sum of the two resistances.

What does Branch Current Method need to solve?

Assign a current to each branch in an active network, Then Kirchhoff’s current law (KCL) is applied at the principal nodes and the voltages between the nodes.

What is each element equal to?

Current will have an independent current, when the branch has the mesh currents, the actual current is given by their algebric sum.

What does a set of equations show in the matrix method?

An expansion of the numerator determinants by cofactors of the voltage terms.

What does the 1,1-element of the node voltage method do?

Contains the sum of the reciprocals of all resistances connected to a node

What does the output resistance do?

Find the short-circuited current between the desired terminals.

How is output resistance found?

Divide the open-circuited voltage to the short-circuited current between the desired terminals

What is a transfer resistance?

Irs is the voltage in one part of a network results in currents in all the network branches.

What is reciprocity?

If a certain voltage in a mesh r gives rise to a certain current in a mesh s, then the same voltage in mesh s produces the same current in mesh r

How does Superposition method help?

If linear, The voltages, branch currents can be obtained with superposition only when the control functions are external to the network containing the sources

How can Thévenin’s and Norton’s Theorems be replaced?

A linear, active, resistive network which contains one or more voltage or current sources can be replaced by a single voltage source and a series resistance (Thévenin’s theorem), or by a single current source and a parallel resistance (Norton’s theorem).

What is maximum power transfer?

Occurs when the power transferred is at maximum, the efficiency is 50 percent