EM 04 - Electric Motors

SAFARI GUIDE: Boone

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OPENING QUESTION: How is radial frequency related to radial angle?

From the sub notes yesterday it sounds like you have a lively class... yay! I was hoping that might be the case.

WORDS/FORMULAE FOR TODAY

TERMS

  • Inductance
  • Magnetic Flux (ΦB)
  • Magnetic Field (B): A vector value
  • Magnetic Force (FB): Also a vector

CONSTANTS:

 

UNITS:

      • Tesla = T defined as 1 N/C(m/s)

FORMULAE:

      • ε = -dΦB/dt = -Bℓv = ∫E ∙ ds
      • ΦB = ∫B ∙ dA
      • B ds = μoI: Ampere's Law
      • dB = oI/4π)(ds x )/r2 (note here is the unit vector like i, j, or k. Biot-Savart Law
      • FB = ∫I ds x B NOTE: AP Version is: FB = ∫I d x B
      • v = E/B
      • FB = qv x B (vector value)
      • FB = qvBsinθ (FB magnitude of only)
      • FB = IL x B

 

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WORK O' THE DAY

Let's see if we can put Lenz's Law to bed by coming up with a:

1) General physics explanation of Lenz's Law

2) An AP Physics 1 explanation of Lenz's Law

3) AP Physics C explanation of Lenz's Law

(this is kinda cool as it talks about 'cutting' the magnetic field lines)

(this one helps with direction of current and pushing/pulling forces)

(this site shows step by step annotations for the previous video)

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WORK O' THE DAY

1) Please write Faraday's Law as we usually do.

2) Now please write the formula that allows us to calculate magnetic flux

3) Try that last one again without calc...

4) Now let's say we're trying to relate that last formula (#3 above) to how quickly an object is rotating (hint: think omega)

5) Now let's chuck in the fact that we're going to be evaluating a coil with N loops... any suggestions?

6) Now please rewrite good ol' Faraday's (#1 above) with the current (#5 above) working formula

7) Now please shorten that a tad to show the MAX emf generated in this situation

Please work through example 31.8 and read the last paragraph in 952

COURSEWORK: Begins on page 963:

31.42, 31.43, 31.45