Math
What does PEMDAS mean?
(),Exponents, X , / , + , -
Good way to remember this is:
Please Excuse My Dear Aunt Sally
Review 305 - 320
What range of electrical shock can cause respiratory arrest?
A. 50 - 150 mA
B. 1 - 5 mA
C. 10,000 mA
Correct answer is
A
Review 325 table 1
Electrons are arranged around the nucleus of an atom in rings or shells. The outermost shell is called what?
Valence Shell
Review 330
All safety circuits needs to be wired in what?
Series
Review 345
Effective value can also be called what?
RMS
Root Mean Squared
Review 360
To add and subtract fractions you must have a common denominator.
How do I multiply and divide? Give me the answer to
1/4 * 1/16 and 1/4 / 1/16
Multiply straight across
1/64
Divide multiply opposite reciprocal
4
Review 305
A dry human body has 100,000 ohms of resistance. If a dry person comes gets between a 120v system and ground will they die?
Most likely no. 120v divided by 100,000 is 1.2 mA generally not enough to kill them.
However if you are damp your resistance could drop to as little as 1,000 ohms.
Review page 6 325
What two formulas are needed to solve basic electricity problems?
P=I*E
E over I/R
A 24v circuit has three 12 watt bulbs in series. What is the circuits resistance?
R = 16 ohms
36W = I * 24v
I = 1.5A
24v / 1.5A = 16 ohms
Review 345
The degree to which a magnetic force can be established in a material is called its permeability. After packing lines of magnetic flux into a material according to its permeability, the concentration of flux lines is called the flux density. What is it called when permeability and flux density hit their max?
Review 355
To from one unit to another you need to find the gap.
What is the gap between Mg and ng?
15 units
Review 310
Are you safe to work on this elevator?
No, the UPS could still be producing power without the three phase power on.
UPS = Uninterrupted Power Supply
Review 325 page 11
A voltmeter must be connected in parallel to read the voltage in a circuit. How much resistance does a voltmeter have?
Infinite
Otherwise is could affect the reading
Bonus: why is a voltmeter connected in parallel?
Review 335
24v circuit with five 500 ohms resistor in parallel. What is the resistance?
100 ohms
1 over 1/500, 1/500.... or
Because all are equal divide by 5
Review 350
Peak to Peak voltage is 270. What is the average voltage?
85.86volts
270 divided in half 135
135 * .636 = 85.86v
Review 360
(x + 4)2-3 = 22
Hint: There are two answers
x = 1, -9
Review 315
You need to change a ballast for the elevator cab lights. There is a light switch in the machine room for the lights. You switch it off and the lights go out.
If you put a lock on this light switch are you safe to replace the ballast ?
No, you need to check the ballast for voltage to a known ground. Due to "electricians" breaking the neutral side of the circuit not the power side.
Switches/Relays are written in what is called switch notation.
There are three parts. What are they in order?
1.poles
2.throw
3.normal position
Example: SPSTNO
Single pole, single throw, Normally open
Review 340
View Circuit. What is the voltage drop across R1?
R1 = 60v
60ohms on each side
1 over 1/60, 1/60 is 30 ohms
120 / 30 is 4A
The 4A is split equally between the two branches.
2A times 30 ohms is 60 volt.
A generator always has 360 mechanical degrees, however if a generator has 8 poles how many electrical degrees does the generator have?
1,440 electrical degrees
Two poles equal 360 electrical degrees
One poles is 180 times 8 is equal to 1,440
Review 360
3 gear system. A is the driver gear and has 30 teeth and turns at 40 RPM. A drives B, and B drives C. Find the RPM of gear B and C if they have 20 and 40 teeth?
Use Formula
Number of teeth A / number of teeth B = RPM B / RPM A
B = 60 RPM
C = 30 RPM
Review 320
No, because the Neutral side of the circuit is not grounded. It would likely operate normally.
You are trying to read a 120v, 100ohm, circuits current. So you get an ammeter and connect it in parallel with the circuit. What reading do you get?
Bonus: why is the ammeter zero resistance and supposed to be connected in series?
Review 335
Redraw circuit from left to right with power on the left and the neutral on the right?
Example: 120v -----resistor------resistor----- N
See picture
There is a 6 pole generator rotating at 3600 RPM. What is the time of each AC cycle?
Hint: t=1/f
3600 / 60 = 60 RPS
6 / 2 = 3 Electrical Cycles per Rotation
3 * 60 = 180Hz
t = 1/180Hz
t = 0.0055sec