Calculating Inductive Reactance — Transcript

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1. 0:04looking at these circuits we have a
2. 0:07problem because our Ohm's law as we know
3. 0:10it already
4. 0:10Ohm's law watts law only deals with
5. 0:13bolts and ohms and power let's just call
6. 0:21it watts for now but we're gonna add a
7. 0:23couple different types of power
8. 0:25different names of power in this class
9. 0:28but nowhere in there is Henry's I don't
10. 0:31have an equation to put in Henry's to
11. 0:33figure out how much current these
12. 0:36circuits will allow so we have this
13. 0:42formula and it's what we use to
14. 0:47determine how much opposition an
15. 0:51inductor will cause in a circuit as the
16. 0:55voltage pushes what will that inductor
17. 0:57push back remember at the beginning with
18. 1:02inductors when I run current AC current
19. 1:06through a conductor it has this magnetic
20. 1:09field around it and that magnetic field
21. 1:11is constantly changing expanding and
22. 1:15contracting positive negative constantly
23. 1:19changing and that constantly changing
24. 1:23nature is what provides the opposition
25. 1:26in an inductor we refer to that as vac
26. 1:29voltage so the applied voltage is this
27. 1:33direction and it pushes up back voltage
28. 1:36on it and that is what provides the
29. 1:39opposition to current flow without that
30. 1:43back voltage that see EMF counter EMF
31. 1:48we'd have to short-circuit all the
32. 1:50current would just flow but that back
33. 1:52voltage provides an opposition and
34. 1:54because it's the way the inductor reacts
35. 1:58to the flow of AC current we call it
36. 2:02reactance the letter X is for reactance
37. 2:06a little sub L
38. 2:09identifies it as inductive reactance
39. 2:13remember L for lens and L for inductance
40. 2:18inductive reactance key term we're gonna
41. 2:22find it's also measured in ohms because
42. 2:25it's a kind of opposition resistors are
43. 2:28in opposition and they're in ohms they
44. 2:31reduce current flow okay
45. 2:34the higher the resistance the less they
46. 2:36will find that the higher your inductive
47. 2:39reactance the less current flows so
48. 2:42let's take a look for three Henry
49. 2:44inductor two times pi times F my
50. 2:53frequency in Hertz cycles per second I
51. 2:59chose 60 that's what most of our
52. 3:02receptacles out of the wall use these
53. 3:03two in in the US so we'll just go with
54. 3:06sixty Hertz times the inductance
55. 3:13measured in henries three do that math
56. 3:19pi being 3.14 or the PI button on your
57. 3:23calculator I'm going to end up with 11
58. 3:2731 and I call them homes because they're
59. 3:32a form of opposition they are not
60. 3:35resistance they are reactance those
61. 3:40terms will become increasingly more
62. 3:42important so our inductive reactance is
63. 3:461131 ohms per inductor my XL
64. 3:54and that will be for all the inductors
65. 3:58because they're all three Henry's apiece
66. 4:01they're all running at 60 Hertz now what
67. 4:06we're gonna find out is this I have a
68. 4:08choice of calculating this inductive
69. 4:14reactive reactance for each inductor and
70. 4:20then totaling my ohms or can I take my
71. 4:28total inductance and use that number to
72. 4:32get the same amount of ohms let's let's
73. 4:37try it and see
74. 4:38so my XL 1 was that my XL two is also 11
75. 4:4531 11 31 now how do you add ohms you add
76. 4:53ohms the same way you always added homes
77. 4:56in a parallel circuit you would use the
78. 5:02inverse inverse operation or product sum
79. 5:05if you just had two and let's see what
80. 5:08that becomes my X L total 377 ohms
81. 5:21because in my parallel circuit my total
82. 5:26circuit opposition will be less than the
83. 5:30smallest of the branch and we'll find
84. 5:32that that rule works out with ohms so as
85. 5:35we've learned so far
86. 5:37inductors operate very much like
87. 5:40resistors when we add them up same rules
88. 5:44for parallel
89. 5:46for the henries and the ohms so we
90. 5:52calculate that at 377 what would this
91. 5:55formula have been if we did 1 Henry
92. 5:59instead of 3 Henry's like that in your
93. 6:04calculator 377 ohms
94. 6:15so it works
95. 6:22let's consider now the series circuit
96. 6:30again that's times three because they're
97. 6:34three Henry's each which we found out
98. 6:37was 11 31 ohms each of these is 11 31
99. 6:45ohms
100. 6:55now when you have ohms in series you add
101. 7:03them up because is your current school
102. 7:06it has opposition here more opposition
103. 7:09more opposition so I'm gonna argue to my
104. 7:13ex LT is an addition of those things
105. 7:1911:31 plus 11 31 plus 11 31 3 3 9 3 ohms
106. 7:32before I write it up here let's check
107. 7:35that formula with 9 Henry's if we say
108. 7:40there is 9 Henry's of total inductance
109. 7:42in the circuit can I simply multiply by
110. 7:469 in this formula and sure enough one
111. 7:51set your calculator 3393 ohms now why do
112. 8:05I go through this process because you
113. 8:08have a choice simplify your Henry's into
114. 8:13the total circuit inductance and
115. 8:15calculate reactance one time or
116. 8:22calculate them individually and some of
117. 8:26the ohms using the proper parallel or
118. 8:29series method your choice
119. 8:36another thing I want to point out here
120. 8:39the way this formula is structured
121. 8:42if the frequency were to increase that
122. 8:48would mean that the the changing nature
123. 8:52of the magnetic field would happen
124. 8:54quicker so that would be more change in
125. 8:59their more reactants that would create a
126. 9:03higher ohmic value or likewise if we had
127. 9:11more inductance we would get a higher
128. 9:16inductive reactance which is truly 3
129. 9:21Henry's equals little over a thousand
130. 9:23nine Henry's well over three thousand so
131. 9:28we want to see how our basic
132. 9:30relationships work