CH 1_BOOK_BASIC CONCEPTS Flashcards
What is an electric circuit?
An interconnection of electrical elements.
What are the 6 basic SI units + 1 derived unit?
What are the 16 SI prefixes? What are their multiplier values and symbols?
Charge is defined as?
Charge is measured in?
Charge is a basic SI Unit (like time, mass, length). It is an electrical property of electrons/protons. It is measured in Coulombs (C).
1 C = ________ e?
1 C = 6.24 x 10^18
Current is defined as the number of ________ passing a given point in one second.
Electrons
What is the magnitude of charge of a single electron/proton?
(-) 1.602 x 10^-19 C
The law of conservation states…
That charge can neither be created nor destroyed, only transferred. Thus, the algebraic sum of electric charges in a system does not change.
Current is defined as?
The number of electrons (charge) passing a given point in one second.
What is electric current?
The time rate of change of charge, measured in amperes (A).
What creates electric current?
The motion of (positive) charges.
What is the formula for current (i) in terms of charge (q)?
1 Ampere = 1 ________/________
1 Ampere = 1 Coulomb/second
What is the formula for charge (q) in terms of current (i)?
What are the two ways that current can flow?
Direct Current (DC) - current flows in one direction.
Alternating Current (AC) - current flows in both directions; changes with respect to time.
Is DC current constant (I) or time varying (i)?
Either constant (I) or time varying (i).
Is AC current constant (I) or time varying (i)?
Only time varying (i).
What is an emf?
External electromotive force; performs the work required to move electrons in a conductor.
Typically a battery.
Also known as ‘voltage’ or ‘potential difference’.
Voltage is defined as?
The difference in electrical potential energy, per unit of charge, between two points.
The voltage/potential difference v^ab between two points a and b in an electric circuit is…
The energy/work needed to move a unit charge from b to a.
What is the formula for voltage v_ab in terms of energy and charge?
A constant voltage is called ________.
DC voltage (V)
A sinusoidally time-varying voltage is called ________.
AC voltage (v).
A DC voltage is commonly produced by ________; an AC voltage is produced by ________.
battery, electric generator
Current is always ________ an element while voltage is always ________ the element or ________ two points.
Through, across, between
What is power?
The time rate of expending or absorbing energy, measured in watts (W).
What is the formula for power in terms of energy and time?
What is the formula for power in terms of voltage and current?
Power is a time-varying quantity and is called the ________. Thus, the power absorbed or supplied by an element is the ________________________.
Instantaneous power, product of the voltage across the element and the current through it.
If the power has a + sign, power is ________ by the element. If it has a - sign, power is ________ by the element.
Gained/absorbed, lost/supplied
How do we know when the power has a negative or positive sign?
Following the standard PASSIVE SIGN CONVENTION:
p = +vi if the current enters through the positive terminal
p = -vi if it enters through the negative terminal.
(opposite for ACTIVE SIGN CONVENTION)
Because of the law of conservation of energy, the algebraic sum of power in a circuit, at any instant of time, must be ________.
zero
+power absorbed = -power supplied
From the power formula p=vi, what is the formula for the energy absorbed or supplied by an element from time t^0 to t?
Energy (J) is?
The capacity to do work.
The electric power utility companies measure energy in ________.
watt-hours (Wh)
1 Wh = _____ J ?
1 Wh = 3,600 J
What are the 2 types of elements in a circuit? What’s the difference?
Passive and active.
An active elements is capable of generating energy while a passive element is not.
What are examples of passive elements?
Resistors, capacitors, inductors.
What are examples of active elements?
Generators, batteries, operational amplifiers.
The most important active elements are ________ sources that generally deliver power to the circuit connected to them.
Voltage/current
What are the 2 kinds of sources?
Independent and dependent.
What is an ideal independent source?
An active element that provides a specified voltage or current that is completely independent of other circuit elements.
An ideal independent voltage source delivers to the circuit whatever current is necessary to maintain its terminal voltage.
An ideal independent current source delivers to the circuit whatever voltage is necessary to maintain the designated current.
In figure 1.11, which of the symbols can be used to represent a DC voltage? What about AC voltage?
What is an ideal dependent (controlled) source?
An active element in which the source quantity is controlled by another voltage or current.
How are dependent sources symbolized?
Diamond shape
What are the 4 possible types of dependent sources?
An ideal voltage source will produce the necessary current required to maintain terminal voltage. Can it be dependent or independent?
It can be either dependent or independent.
If sources supply power to a circuit, can they absorb power from a circuit too?
Yes.
For a voltage source, we know the voltage but not the current supplied or drawn by it. By the same token, we know the current supplied by a current source but not the voltage across it. True or false?
True.
Can voltage and current sources be dependent or independent?
They can be either.
