AP_Physics_B_-_Magnetic_Fields_and_Forces

# AP_Physics_B_-_Magnetic_Fields_and_Forces - AP Physics B...

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Magnetic Fields and Forces AP Physics B

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Facts about Magnetism Magnets have 2 poles (north and south) Like poles repel Unlike poles attract Magnets create a MAGNETIC FIELD around them
Magnetic Field A bar magnet has a magnetic field around it. This field is 3D in nature and often represented by lines LEAVING north and ENTERING south To define a magnetic field you need to understand the MAGNITUDE and DIRECTION We sometimes call the magnetic field a B-Field as the letter “ B ” is the SYMBOL for a magnetic field with the TESLA (T) as the unit .

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Magnetic Force on a moving charge If a MOVING CHARGE moves into a magnetic field it will experience a MAGNETIC FORCE. This deflection is 3D in nature. N N S S - v o B θ sin qvB F B v q F B B = = The conditions for the force are: •Must have a magnetic field present •Charge must be moving •Charge must be positive or negative •Charge must be moving PERPENDICULAR to the field.
Example A proton moves with a speed of 1.0x10 5 m/s through the Earth’s magnetic field, which has a value of 55 μ T at a particular location. When the proton moves eastward, the magnetic force is a maximum, and when it moves northward, no magnetic force acts upon it. What is the magnitude and direction of the magnetic force acting on the proton? = = = = = - - B B B F x x x F qvB F ) 10 55 )( 10 0 . 1 )( 10 6 . 1 ( 1 90 sin , 90 , 6 5 19 θ 8.8x10 -19 N The direction cannot be determined precisely by the given information. Since no force acts on the proton when it moves northward (meaning the angle is equal to ZERO), we can infer that the magnetic field must either go northward or southward.

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Direction of the magnetic force?  Right Hand Rule To determine the DIRECTION of the force on a POSITIVE charge we use a special technique that
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