Week #3 Flashcards
What are the two commonly performed functions of a resistor in an electrical circuit?
Limit the flow of current throughout the circuit and voltage divider
What is a voltage divider?
Any voltage can be obtained
What is the general voltage divider formula?
I = E/R
When using resistors of a proper value, for the purpose of greeting, a voltage can almost enable voltage desire be obtained
Yes
When there is no resistor in a circuit and unlimited current is allowed to flow this is known as what
Ideally, if there is no resistance ,i.e, short circuit is connected across an dc source, infinite current will flow as I=V/R, and R=0. 2.
A resistor that has only one resistance value that cannot be charged or adjusted is known as what type of resistor
A fixed resistor
What is one of the most common type of fix resistors?
Composition carbon resistor
What are the composite carbon resistor composed of?
Compounds of carbon graphite, and a resin bonding material
What determines the value of the resistor?
The proportions of carbon and risen material determines the value of resistance
Why are carbon resistors popular?
Inexpensive and readily available
The larger the diameter of the resistor indicates what with regards to its power rating
Greater Watts
What happens to carbon resistors as they age or if they get over heated
The increase instead of decrease in value
A resistor with a tolerance range of 20% 10% or 5% is what type
Metal film resistors
A register with the tolerance range of 2% to one percent is what type
Wire around resistors?
How are wire round resistors made?
By winding a piece of resistance wire around a ceramic core
The resistance of a wire around resistor is determined by what three
Factors
The type of material used to make the resistance wire, the diameter of the wire, and the length of the wire
What advantage is there to use a wire round type of resistor?
For high power rating ii can operate at higher temperatures
What is used as a visual aid to determine the value of resistor?
Colour code
Does each colour represent a number value when using the colour code to determine the value of a resistor?
Yes
How many colour bands can resistors
3 to 5
A resistor with only three colour bands will have tolerance of what
Plus or -20%
The third band in a five band resistor does what function
Number value
What does the tolerance band actually indicate?
The range of resistance plus or minus the tolerance colour indicate
Ask Jeff, the saying he uses to remember the colour code chart
Bad beer, rots our young guts, but vodka goes well
Why should we not exceed the power rating of a resistor?
The resistor will be damaged
A resistor that can change or very its resistance over a specific range of resistance is known as what
A variable resistor
How do variable resistors generally work?
The value of resistance can be adjusted between one end of the resistive wire and sliding tab
What are the two most common types of variable resistors?
Wire around variable resistors and multiturn variable resistor
What does the acronym MM stand for?
Multimeter
A MM that uses a pointer and a scale to indicate the tested value is known as what type of metre
Analogue metres
What type of movement is used in the analog metre shown
Movement-coil meter
Another type of metre movement that allow analog metres to which use is a magnetic field and either attracts or repel the iron vanes, which are attached to the pointer is known as what
Gelvanometers
How does an analog metre work?
Magnetic poles repel each other
What type of MM do we get with our tool kids?
Digital multimeter
How does a digital MM work?
Putting the black pin on common and red on hot, selecting the dial to the right unit and reading the measurements on the screen
Are all MM accurate?
No
When taking a measurement, is it important to select the correct scale pro placement and correct symbol on the selector switch
Yes
Is human error and metre failure a dangerous issue?
Yes
Is human error and metre failure a dangerous issue?
Yes
How does an MM measure voltage in AC or DC circuits?
By connecting the prong to any part of the circuit
How does Emma measure current not clamped on an AC or DC circuit?
It must let the current flow through the circuit, so basically unconnected the circuit and connect with the multimeter until the circuit works again
Can you use a clamp on MM to measure current in an AC circuit and why
No cause it will blow a fuse on your multimeter
Can you use a clamp on MM to measure current in a DC circuit?
No cause it will blow a fuse on your MM
A lower resistance device that conducts most of the circuit DC current away from the metre movement which then lasts 1 m³ movement to read multiple currents is known as what
Ammetre shunts
Do multiple range DC and metres use multiple shunts
Yes
Can you build your own DC shunt using a resistor and ohms law?
Yes
What is the formula for calculating the resistor values for an Aytron shunt?
Rs = Im X Rm/ It
RS equals resistance of the shunts I am equals current of the metre movement RM equals resistance of the metre movement IT equals total circuit current
What is the purpose of using a shunt in an AC ammeter?
To increase the range, but cannot be used to decrease the range
A advice that uses two sets of Winings primary and secondary that are close in proximity that depending on the number of turns can increase or decrease the voltage utilizing a magnetic field is known as what
Current transformer
A CT or current transformer is a single set of winding much like the secondary windings of a standard transformer what purpose of a CT
When a large amount of AC must be measured, a different type of current transformer is connected in the powerline
What enables a CT to be able to be utilized from a very high current situation right down to the very small current situation
The turn ratio of the transformer can be changed by looping. The power wire through the opening in the transformer, a primary winding of more than one turn.
What is an ohmmeter?
The ohmmeter is used to measure resistance
Can we use an old metre when the circuit is energized?
Yes
Do the MM that come with the tool kits have the ability to measure multiple ranges of the following voltage, AC and DC resistance and capacity
Yes
Can we measure power of watts with a MM from the tool kit?
No, we must find power with ohms law by measuring resistance X volt
If you wanted to know how much power or watts a circuit was using what must we do?
Use law and find amperage voltage or resistance
Can you purchase a wattmeter?
Yes but expensive
What are the two basic types of wattmeter?
Electrodynamicmetre wattmetre and induction watt metre
A device that uses an X and a Y axis to visually display any electoral waveform is known as what
Oscilloscopes
The X axis on the oscilloscope represents what with regards to the waveform
Time
DY axis on an oscilloscope represent what with regards to the waveform
Voltage
When looking at an AC waveform, what is VPN RMS value?
VP equals peak voltage RMS equals root mean square
How do we calculate the frequency f measured in hertz of an AC waveform
f=z/t
Any equation answered above what is base unit of measurement required for time?
Seconds or microseconds
What is the formula for calculating tea or period of a weight form and what unit of measurements is used for Period.
period = 1/frequency
T = periods
We can calculate an amplitude by using 1/2 of the distance between the crest, positive peak and through negative peak so if the waveform is centred on the horizontal axis of the cell and the peak is five, which is one volt increments above the axis and through is 51 V increments below the axe the total distance would be 10 in increments so what would be a or amplitude of the waveform be
50A
What formula do we use to calculate the velocity v of a waveform using frequency f and wavelength?
v= f X ^
A wavelength unit of measurement is in what
Meter
When shown on the board wavelength and period are indicate to be the same measurement but what is the main difference?
Wavelength is the distance between two identical points in the cycle of a wave. Period Is the time it takes to complete one cycle of the wave?
What is a Megger?
To measure insulation resistance
How does megger work?
It applies a high voltage to the current and measures the amount of current that flows through the insulation
List the two types of megger that are listed in the book
Electronic type and portable type
