Lesson 9
MAGNETIC FLUX
Announcements
Magnetism HW #6 & 7 due TODAY (FR 1 & 2)
Magnetism HW #9 due Thursday
Physics Bowl Thursday 6th & 7th periods
Monday AM review
– Bring your questions about the packets!
Mock AP – Monday 6:30PM
– Bring several sharpened #2 pencils
– Do NOT bring scratch paper, calculators, or cell
phones (leave in your car!)
– Make-up 6AM Tuesday
AP Review Packets –
optics, waves, modern due Wednesday, April 10
AP Physics B Learning Objectives
III.E.1. Electromagnetic Induction
a) Students should understand the concept of magnetic
flux, so they can:
(1) Calculate the flux of a uniform magnetic field through a loop
of arbitrary orientation.
Student Learning Objectives
Students will be able to
1. Determine the magnitude of the magnetic flux
through a loop of wire.
2. Determine how the magnetic flux varies with angle.
Magnetic Flux
The product of magnetic field and area.
Can be thought of as a total magnetic
“effect” on a coil of wire of a given area.
B
A
Area Vector
Consists of the measured or calculated area
(the vector’s magnitude) with a direction
normal to the area’s surface.
Maximum Flux
Can you draw the loop so that the flux is
maximum through the area? Make sure
you draw the area vector!
B
A
Minimum Flux
Can you draw the loop so that the flux is
minimum through the area? Make sure
you draw the area vector!
B
A
Intermediate Flux
Can you draw the loop so that the flux is
neither maximum nor minimum through the
area? Make sure you draw the area vector!
B
A
Magnetic Flux
B = B A cos
– B: magnetic flux in Webers (T m2)
– B: magnetic field in Tesla
– A: area in meters2.
– : the angle between the area and the
magnetic field.
 B = B A
Sample Problem 9.1:
Calculate the magnetic flux through a rectangular wire frame 3.0 m long
and 2.0 m wide if the magnetic field through the frame is 4.2 mT.
a)
Assume that the magnetic field is perpendicular to the area vector.
b)
Assume that the magnetic field is parallel to the area vector.
c)
Assume that the angle between the magnetic field and the area vector is
30o.
Sample Problem 9.2:
Assume the angle is 40o, the magnetic field is 50 mT, and
the flux is 250 mWb. What is the radius of the loop?
B
A