Elect Theory N Safety Flashcards
2 main categories of resistors
- fixed
- variable
3 basic types of fixed resistors :
- Composition resistors
- film resistors
- wire wound resistors
The most commonly used fixed resistor :
Composition
2 types of variable resistors
- Rheostats
- potentiometer
Basic difference between rheostat and potentiometer
Rheostat has 2 connection points
Potentiometer has 3
Res value
A) 2R2
B) 220k
C) 2M2
A) 2.2 ohm
B) 220 000 (×1000)
C) 2 200 000 (× million)
Resitor color code 1st color
1st digit
Resistor color code 2nd color
2nd digit
Redistor color code 3rd color
Multiplier
Resistor color gold
a) 4th position
B) 3rd position
A)+- 5%
B) .1
Resistor color code silver
A) 4th position
B) 3rd position
A)+- 10%
B) .01
Resistor color code no 4th band
+- 20%
Resistor color code black:
A) first color
B) second color
Both are 0
If there are more than 4 color bands:
1 to 3) #s
4) multiplier
5) tolerance
6) temp coefficient
Resistor color code yellow,violet, red, silver rating
4700 +- 10% (4.7 k ohm)
Res colors green,black,brown rating
500 ohms +- 20%
3 distinct ratings of resistors
A) resistance (ohms)
B) power (watts)
C) tolerance
Resistor color code
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Grey
White
Gold
A material with easily freed electrons is called
A conductor
Def: static electricity
Build up of charge in an insulated object
Static electricity:
Build-up of charge in an insulated object
A ______ represents the quantity of charge of a huge # of electrons
Culomb
Def amp ,:
Current formula
Rate of movement of charges past a point
Current = quantity of charge/ time
Conventional current flows from ____ to _____
Positive to negative
If current flows from - to + it is _____ flow
Electron
Why dont you connect an ammeter in parallel:
The low resistance of the ammeter will cause a large current flow and blow the fuse
Voltage is derived :
From the measurement of difference in charge
6 sources of emf
1) magnetic
2) chemical
3) friction
4) heat
5) pressure
6)light
Formula for conductance
G = 1/R
Ohms law
V / I ×r
What force maintains a difference in charge?
Its abbreviation?
Electromotive force
Emf
4 factors affecting conductor resistance
1) cross sectional area
2) length
3) type of material
4))temp of material
Resistance is directly _____ to conductor length
Proportional
Resistance is ______ to conductor cross sectional area
Inversely proportional
For most materials increase temp causes:
Increased resistance
At 20 degrees what is the resistivity of copper
1.72 × 10 ^-8
At 20 degrees what is the resistivity of aluminum
2.83 ×10^-8 ohms
Copper ohms per 1000m, how does it increase,?
3.27
Doubles every 3 gages ie:away 13 is 6.54, 16 is 13.08
Or goes up × 1.26 each gage
Base unit for temp
Kelvin
Base unit for amount of substance
A mol
Conductor resistance formula:
Ohms = resistivity × length / area
Resistivity is in ohm- meters
Temp resistance formula
R2 =R1(1+a(t2 -t1))
R1 initial temp res
a temp coefficient
T2 new temp
T1 initial temp
Dielectric strength def,:
Voltage required to cause a breakdown in insulation
Unit for dialectic stength
Volts per millimeter
Mili def
10 ^-3
Micro def
10 ^ -6
Nano def :
10 ^-9
Pico def
10 ^-12
A copper conductor is 150m long and has a resistance of .76. Whats the cross sectional area?
1.72 ×10^-8 ×150m /.76
= 3.4× 10^-6 m^2
Or 3.4 mm^2
To measure the ohms for volt drop
De energized check across the load
Valence electrons for
- conductors
- insulators
- semi
- 1 to 3 cond
- 4 semi
- 5 to 8 insul
Every 3 db _____ the strength of the noise
Doubes
3 power calcs
P = VI
P =( V ^2)/ R
P = I^2 R
Min battery voltage after supplying amp hour rating?
91% of Max
Voltage leads current in an _____ circuit
Inductive
Current leads voltage in a _____ cct
Capacitive
Series cct :
Res
Volt
Amps
Add ohms
I is same
V different
Parallel cct
Res
Volt
Amps
1 over ( 1 / res 1) (1 / res 2)
Volts same
Current varies
In a series cct if R1 ohms are 3x larger than R2 then R1 voltage is ______ than R2
3x larger
Series cct voltage across closed switch
0v
Series cct voltage across open switch
Applied voltage
Kirchoffs voltage law states:
The algebraic sum of all voltages in a closed cct = 0
Parallel cct:
RT = 15.
R1 = 30
R2 = 120
R3 = x
X = 40
Parallel cct
E =12 v
R1 = 24
R2 = 24
R3 = 12
Rt =? It =? R1 I?
Rt = 6 ohms
It = 2a
R1 i = .5a
Kirchoffs current law:
All the current values entering a junction must equal the current values leaving a junction
Def : inductance
Property of a cct that opposes change in current
Def induction
Process by which h a voltage is produced by the interaction of a conductor and a magnetic feild
Amount of emf is directly proportional to change of flux is whos law
Faradays
Current from an induced voltage develops a flux that opposes a change in the original flux is whos law
Lenz’s law
With a coil what 4 factors up inductance
1) more turns
2) higher permeability
3) bigger core area
4) shorter path
Class 1 area def:
Flammable gasses n vapours
Class 2 area def:
Dust
Class 3 area def:
Igniteable fibers/ flying
Zone 0 def
Hazard present most of the time under normal conditions
Zone 1 def:
Next to zone 0 , flammable gasses vapors likely more than 10 but less than 1000 hrs/yr
Zone 2 def
Next to zone 1. Explosive conditions don’t normally exist . Less than 10 hrs/yr
When generating voltage what 3 factors determine the amount
- density of flux
- length of conductor in mag feild
- rate at which it cuts lines of force
Def : 1 alternation
# of degrees
When a conductor passes 1 pole
180
Def : 1 cycle
2 alternations
Difference between generator and alternator
Generator: rotating conductor, stationary feild
Alternator: opposite
If Vpk is 10v and sine @ 20 degrees:
Voltage is:
Vpk × sin20
10 × .342
3.42 v
120v 60 hz supply. In series:
-20 ohm resistor
- 20 Xl / 5 ohm coil
- 12 Xc capacitor
Zt? It?
Xt 20 - 12 =8 vars
Rt 6 +5 ohm = 11 ohm
Pythagoras = 13.6 Ohm Zt
120/ 13.6 = 8.82 It
of time constants to reach steady state
5
% increase per time constant
63.2%
Frequency calc formula: on a generator
F =( # of poles × rpm) / 120
Max volts of 120 v cct
Min
120 / .707(sin 45) = 169.7
120 × .707 = 84.84
Def power
Unit
Rate of doing work
Watt
Power formula ( watts)
Energy/time ( j/s)
A primary cell is
Non rechargeable
Battery: secondary cell
Rechargeable
Retentivity
Ability of a material to retain residual magnatism
Silicone steel reduces
Hysteris losses
Laminations reduce
Eddy current losses
60/40 solder is made of
60 % tin
40 % lead
Can you use crimps on solid wire?
No
Wattage of a soldering gun
Usually about 40
Electronics: what is EPA
Electrically protected area
Electronics what is ESD
Electro static discharge
Temp coefficient of aluminum/ copper
. 0039
Efficiency of a 1.5 hp motor that draws 10 A from a 120 V supply
((746 × 1.5) / 10 A × 120 V ) × 100%
93.25 %
A 90 amp hour 12v battery can deliver ___ amps for 30hrs and not drop below _____ volts
1) 90/30 = 3a
2) 12 × .91 = 10.92
Normally what direction does magnetic flux travel, which pole to pole
North to South
Right hand rule :
1) thumb
2) 1st finger
3) 2nd finger
1) direction of current
2) direction of flux
3) direction of force
Ac positive alternation is ____ degrees
Negative is _____ degrees
0 - 180
180 - 360
Dc time constant
Cct is 12vdc has an inductor with 3 ohms n .2 henries. How long to reach steady state?
Current: 12 / 3 =4
T = L/R : .2/3 = .67
5 time const so .67 x5 = .33 sec
