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Introduction to Active Learning: Faraday

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Introduction to Active Learning: Faraday s Law – PowerPoint PPT presentation

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Title: Introduction to Active Learning: Faraday


1
Introduction to Active Learning Faradays Law
2
Todays Objectives
  • Introduce key concepts from electricity and
    magnetism through discovery activities,
    experiments, concept questions, discussion, and
    visualizations.
  • Later in the course, we will return to the same
    concepts.
  • Today we are just going to have some fun and
    get to know each other.

3
Introductions
4
What we are trying to get a feel for
You Tube Link http//youtu.be/YywaJkGKOaY
5
Concept Question Loop in Uniform Field
While a rectangular wire loop is pulled upward
though a uniform magnetic field B field
penetrating its bottom half, as shown, there is
  1. a current in the loop.
  2. no current in the loop.
  3. I do not understand the concepts of current and
    magnetic field.
  4. I understand the concepts of current and magnetic
    field but am not sure of the answer.

5
6
Demo aluminum sleeve moving past fixed magnet,
students do this at their tables Demo we show
the demo of magnet falling through plastic tube
and aluminum tube
7
Seeing the Unseen Faradays Law Applet
Applet -- Faradays law applet (with a magnet and
a coil) http//web.mit.edu/viz/EM/visualizations/
faraday/faradaysLaw/faradayapp/faradayapp.htm Play
with the application until you are familiar with
all the features. In the Actions Menu try both
Manual and Generator Mode. You can use the
buttons at the bottom to start, pause and reset
the simulation. You can move the magnet and the
ring back and forth using the mouse. Let each
person in the group have a turn.
8
Seeing the Unseen First Concept Flow Group
Discussion Question
What are some examples of flow of something
through an area?
9
Examples of Flow Electric Current Flow Of Charge
Electric Current I Charge ?Q flowing across area
A in time ?t
10
Current and Magnetic Field
Current produces a magnetic field as shown in
figure
11
Magnetic Field of Bar Magnet
(1) A magnet has two poles, North (N) and South
(S) (2) Magnetic field lines leave from N, end at
S
12
Seeing the Unseen Magnetic Field
Run the Applet on generator mode and stop the
magnet when it is near the ring Scroll down on
the panel on the right and click on Magnetic
Field Iron Filings
13
Seeing the Magnetic Field Iron Filings
The iron filings represent the magnetic field
present at the instant you stopped the magnet .
The direction of the magnetic field is along the
direction of the iron filings. Does the magnetic
field intercept the area of the circular wire?
14
Magnetic Flux Thru Wire Loop
Flux is the Generalization of Flow Product of
magnetic field and area
15
Discussion Question Magnetic Flux in Ring
The first graph on the right in the Applet shows
a plots of the external magnetic flux and total
magnetic flux in the ring versus time. Briefly
describe where the external flux (red plot) is
coming from that is, what kind of flux is this,
what creates it, over what area is the flux being
measured.
16
More Discussion Questions About Magnetic Flux
  • Describe different ways that you can change the
    external flux
  • Explain how the total magnetic flux (blue plot)
  • is related to the external magnetic flux
    (red plot).

17
Current in Ring
The second graph on the right in the Applet shows
a plot of the current in the ring versus time.
18
Proposing a Hypothesis
Propose a qualitative relationship between
magnetic flux (seen in top graph) and current
that flows in the ring (seen in bottom graph).
19
Testing Hypotheses
  • Groups utilizing the application came up with the
    following hypotheses.
  • Group A conjectured that the current through the
    ring is proportional to the total magnetic flux.
  • Group B proposed that the current through the
    ring is proportional to the change in the total
    magnetic flux.
  • Use the application to test these two hypotheses.
    Design and run a virtual experiment that could
    rule out any of the hypotheses. Which did you
    rule out and why?

20
Faradays Law of Induction
Changing magnetic flux induces a current
20
21
Electromotive Force, Current and Resistance
Vary the resistance in the applet and observe the
current. Electromotive force looks like a
voltage difference. Its a driving force for
induced current
22
Faradays Law of Induction
Changing magnetic flux is proportional to
electromotive force
22
23
Demo Electromagnetic Induction
24
Demo Electromagnetic Induction
25
Demonstration Induction At this point,
students again move the coil of wire in their
experiment just to observe the current
26
Concept Question Loop in Uniform Field
While a rectangular wire loop is pulled upward
though a uniform magnetic field B field
penetrating its bottom half, as shown, there is
  1. a current in the loop.
  2. no current in the loop.
  3. I do not understand the concepts of current and
    magnetic field.
  4. I understand the concepts of current and magnetic
    field but am not sure of the answer.

26
27
Concept Question Answer Loop in Uniform Field
Answer 1. The motion changes the magnetic flux
through the loop. The magnetic flux is decreasing
in time as more of the loop enters a region of
zero magnetic field. According to Faradays Law
there is an induced current through the loop.
27
28
Concept Question Loop in Uniform Field
While a rectangular wire loop is pulled sideways
though a uniform magnetic field B field
penetrating its bottom half, as shown, there is
  1. a current in the loop.
  2. no current in the loop.
  3. I do not understand the concepts of current and
    magnetic field.
  4. I understand the concepts of current and magnetic
    field but am not sure of the answer.

28
29
Concept Question Answer Loop in Uniform Field
Answer 2. The motion does not change the
magnetic flux through the loop. The magnetic flux
is constant in time. According to Faradays Law
there is no induced current through the loop.
29
30
Lenzs Law Direction of Induced Current
31
Discussion Question Induced Current
Run the Applet and observe the relation between
the sign of current and the slope of the plot of
magnetic flux. What do you observe? Try flipping
the coil and see what result you get for the
current.
32
Minus Sign? Lenzs Law
Induced EMF is in direction that opposes the
change in flux that caused it
33
Concept Test Induced Current
We define positive current clockwise as viewed
from the top. As the coil moves from well below
the magnet to well above that magnet, the induced
current through the coil will look like
Try to answer this question using your
experimental set-up
(1) (2)
(3) (4)
(5) I dont know
34
Concept Question Induced Current Answer
Solution (3).
35
Conclusion Faradays Law of Induction
Changing magnetic flux generates electromotive
force that opposes that change in flux
35
36
Jumping Ring
  • An aluminum ring jumps into the air when the
    solenoid beneath it is energized

37
What is Going On?
This is a dramatic example of Lenzs Law When
the magnetic field created when the solenoid is
energized tries to permeate the conducting
aluminum ring, currents are induced in the ring
to try to keep this from happening!
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