Electricity 4 of 7 Flashcards
The term “phase angle” is used to describe the ___________ ___________ between a-c voltages and currents, as well as to specify a position or point in time of one a-c voltage or current.
Time relationship
In a purely _________ circuit, the voltage and current are in phase.
Resistive
In a purely ____________ circuit, the applied voltage leads the current by 90 degrees.
Inductive
In a purely _______________ circuit, the current leads the applied voltage by 90 degrees.
Capacitive
Every physical quantity has?
Magnitude
What do you call a quantity that only has a magnitude?
Scalar
What do you call a quantity that has magnitude and direction?
A vector
The _________ of the __________ is proportional to the magnitude of the vector quantity, and the ___________ indicates the direction.
Length of the line
When looking at a vector, what axis serves as the reference line?
Horizontal axis
In our line of work, we will only be interested in the ___________ and _________ of vectors. (Think math)
Addition and subtraction
When vectors are added or subtracted, the result is also a vector, and is called the _________ __________.
Resultant vector or just resultant
What combination of math is used to add and subtract vectors?
Geometry and algebraic addition and subtraction
To add vector quantities that have the same direction you?
Add the individual magnitudes.
To add vector quantities that have different directions you?
Subtract the smaller vector from the larger vector.
When vectors are not going in the same direction or in opposite directions, they can be added graphically and the resultant can be found using the __________ ____________ method.
Parallelogram method
What’s the first thing you do when adding vectors using the parallelogram method?
Place the vectors “tail to tail.”
The ___________ line is the resultant of the vectors after they have been placed tail to tail.
Diagonal (hypotenuse)
Another method for adding vectors is the triangle method and involves laying the vectors __________ to _________.
Head to tail.
The resultant of the triangle method is the line that starts at ____ ___________ of the first vector and ends at ____ ______ of the second vector.
The tail The head
Vectors that are not in same direction or in opposite directions are __ degrees apart.
90
The magnitude of the resultant of vectors, that are 90 degrees apart, can be determined by using what equation?
Pythagorean theorem
The sum of the angles in a right triangle equals?
180 degrees
What is opposite of the right angle of a triangle?
The hypotenuse
What 3 trigonometric relationships can be used to find the angles of a triangle?
1- sine 2- co-sign 3- tangent
When subtracting one vector from another, add the ___________ equivalent by rotating the vector 180 degrees.
Negative
When rotating a vector 180 degrees to get its negative equivalent, what effect does this have on its magnitude?
None.
Can a vector be separated? If so, what are their parts called?
Yes, and their parts are called the horizontal component and the vertical component.
When adding vectors by there components, what must be determined before drawing the resultant vector?
The direction
A-c vectors are called?
Rotating vectors
A vector is _____________ until compared with the direction of another voltage or current vector.
Meaningless
The length of a vector shows its_________, while the angle between the vectors shows the _______.
Amplitude Phase
The angle between any vector and the reference vector is measured in the direction that will make it less than?
Less than 180 degrees
A waveform shows what values?
Instantaneous
What values do vectors provide?
Effective values, such as; peak, average, or effective value of the amplitude.
An RL circuit contains both?
Resistance and inductance.
In this circuit, resistance is the only opposition to current.
Resistive circuit
In this circuit, inductance is the only opposition to current flow.
Inductive circuit
Only quantities that vary in _________ can differ in phase?
Time
What is the symbol for impedance and what is it measured in?
Z Ohms
When can the value of resistance in a circuit be neglected?
When the other value is 10 time the resistance value.
The voltage drop across a resistance is __ ______ with the current that causes it, while the voltage drop across an inductance _________ the current by 90 degrees.
In phase, Leads
How do you find the voltage in a series RL circuit?
By using Pythagoras theorem
How equation determines the phase angle between the voltage applied to the resistor and the applied voltage to the inductor?
Tan of(EL/ER)
What does Impedance represent?
Total opposition to current flow.
In resistive circuits, _____ of the Power delivered by the source is dissipated by the load.
All
In an RL circuit, only part of the power delivered is dissipated. Where does the rest go?
It’s returned to the source each time the magnetic field collapses.
What two types of power are in RL circuits?
Apparent and true power
What power is is used by the resistance in an RL circuit and what is its equation?
True power. Ptrue=I^2R
What is the power factor equation?
True power/apparent power
What is the Q of a coil and what is the equation?
The Q of a coil is how close the coil is to being a perfect inducer and is a ratio of the reactance to the resistance of a coil. Q=XL/R
The voltage across every branch in a parallel RL circuit is?
The same as the applied voltage.
Is there a phase difference of current in a parallel RL circuit?
Yes, the resistive legs current is in phase with the voltage while the voltage in the inductive legs leads the current by 90 degrees.
Since current in an RL circuit is out of phase, what equation is used to find their vector sum?
Pythagoras theorem
In a RL circuit, resistive current _________ the inductive current by __ degrees.
Leads 90
How Does increased frequency in a parallel RL circuit affect impedance?
The higher the frequency, the closer the impedance gets to the value of the resistance; making the circuit more resistive.
How does frequency affect impedance in a series RL circuit?
A higher frequency increases the impedance of the circuit making the circuit more inductive
