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Final

Physical Sciences 3 Lecture Notes - Lecture 13: Michael Faraday, Experimental Physics, Scandinavian MountainsExam


Department
Physical Sciences
Course Code
Physical Sciences 3
Professor
Roxanne Guenette
Study Guide
Final

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Physical Sciences 3: Lecture 5c
March 14, 2019
1
Electromagnetic Induction
The magnetic flux of the field
B
through an area
A
is:
ΦB=
B
A=BA cos
θ
, where
the area vector
A
determines the orientation around the edge according to the right-hand
rule. Usually we’ll be interested in the magnetic flux through a loop of wire.
You can change the magnetic flux by changing the area of a loop, changing the
magnitude of the magnetic field, or changing the angle between the magnetic field
vector and the area vector.
Faraday’s Law of Induction says that a changing magnetic flux will induce an EMF in
a loop of wire. This induced EMF will cause current to flow in the wire. The
relationship between flux and EMF is:
ε
induced =dΦB
dt
The minus sign in Faraday’s Law reminds us that the induced current will create a
magnetic field that counteracts the change in flux. This is known as Lenz’s Law. One
strategy for using Lenz’s Law is as follows:
1. Choose your area vector to point in the same direction as the original field.
2. This way, the flux will be positive. Is the flux increasing or decreasing?
3. Determine the direction of the induced field to counteract the change in flux.
4. Use the right-hand rule to find the direction of the induced current.
Learning objectives: After this lecture, you will be able to…
1. Define the magnetic flux through a loop of wire, and calculate the flux for a given
magnetic field and loop (including the sign of the flux).
2. Describe what you can do to change the magnetic flux through a loop, and decide
whether the magnitude of the flux gets larger or smaller for each type of change.
3. Explain Faraday’s Law of Induction and how it relates changes in magnetic flux with
induced current in a loop.
4. Use Lenz’s Law to determine the direction of the induced current in a loop.
5. Calculate the magnitude and direction of the induced current in a loop of wire, given the
change in the magnetic flux and the resistance of the wire, using both Faraday’s Law and
Lenz’s Law.

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�0 yt c
YBo �H•
1

Only pages 1-3 are available for preview. Some parts have been intentionally blurred.

Physical Sciences 3: Lecture 5c
March 14, 2019
2
Magnetic Flux
We need to define a quantity called magnetic flux:
Given a small area A and a magnetic field B, we can
define the flux as:
ΦB=
B
A=BA cos
θ
It will be important to define a direction around the perimeter based on the choice of
direction for the area vector
A
using the right hand rule.
Can the magnetic flux be negative? Yes! It depends on your choice of the area vector:
direction around perimeter
area vector A
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