Download AP Physics Lesson 48

Warm Up
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Grade the HW
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105 Pts
AP Physics
Lesson 48
Magnetic Fields
Electricity and Magnetism
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A match made in heaven?????
Parts of a magnet
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North vs. South
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Not the Civil War
North is attracted to South
The north end of a magnet aligns with the
North Pole
Magnets
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Magnetic Domains
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Aligned creates a magnet
Electron spin
How to make a magnet
How to make a magnet go bad
Magnetic Fields
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Force fields around magnets
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Created by moving electric fields generated by
a moving charge
Symbol for magnetic field is B
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Measured in units of Tesla (T)
Drawing Magnetic Fields
Drawing Magnetic Fields
Drawing Magnetic Fields
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Use multiple lines to show uniform
magnetic fields
3D
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Into the page (x)
Out of the page (.)
Magnetic Force
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Magnetic fields create forces on moving
charges
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Causes a change in direction
Proportional to the size of charge
Proportional to the speed of the charge
Proportional to the size of the field
FB
Magnetic Force
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FB = qvBsinθ
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A charge moving at an angle to the field
experiences less of a force
Helical Motion
Right Hand Rule
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Helps us predict the direction of the force
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Predicts which way the charge will be
deflected
RHR
Example I
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A proton moving from left to right with a
velocity of 305m/s enters a magnetic field
that is perpendicular to the plane of the
paper (coming out of the page). The
strength of the field is 44T. Find the
magnitude and direction of the force on
the proton as it enters the field.
Answer
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2.1x10-15N down.
Example II
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An electron travels at 2.0x107m/s to the
right at it enters a 0.010T magnetic field
directed into the page. A) Determine the
magnitude of the force acting on the
charge. B) Determine the direction of the
force. C) Sketch the magnetic field and
path the charge takes. Describe the path
as moving either clockwise or
counterclockwise.
Answer
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3.2x10-14N down and clockwise.
Example III
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A charge of 8.1x10-9C enters a magnetic
field with a speed of 2200m/s at an angle
of -30°. The 4.0T magnetic field is
moving from left to right. Determine the
magnitude of the force the field exerts on
the charge.
Answer
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3.6x10-5N.