prev

next

of 28

View

212Download

0

Embed Size (px)

Transcript

MagnetismAP PhysicsChapter 20

Magnetism20.1 Mangets and Magnetic Fields

Magnets and Magnetic FieldsObjects that align with the magnetic field of the earth. The north pole is magnetic southpoleLike poles repel and unlike poles attractUnlike charges, polescan not be isolateIf a magnet is cut, new poles appear20.1

Magnets and Magnetic FieldsMagnetic field lines look similar to electric field lines Point in the direction of a force on a North monopoleInteraction is also similar to electric fields

20.1

Magnets and Magnetic FieldsThe earths magneticfield Caused by the iron coreDoes not point to geographic North Provides protectionagainst solar wind

20.1

Magnetism20.2 Electric Currents Produce Magnetic Fields

Electric Currents Produce Magnetic FieldsHans Christien Oerseted 1820 a compass needle deflects when a current is first produced in a wireThe field is in a circle around thewireWe can determinethe directionof a magnetic field using theright hand rule20.2

Electric Currents Produce Magnetic FieldsRight hand rule #1 1. the thumb points in thedirection of the current 2. the fingers curl in the direction of the magneticfieldA magnetic field due to a loop20.2

Magnetism20.3 Force on an Electric Current in a Magnetic Field

Force on an Electric Current in a Magnetic FieldMagnets exert force on a current-carrying wire (Newtons Third Law)The force is 1. perpendicular to the direction of current 2. perpendicular to the direction of the magnetic field

20.3

Force on an Electric Current in a Magnetic FieldRight Hand rule #2 1. fingers, direction of magnetic field 2. thumb, direction of current 3. palm, direction of forceThe force is defined as

B magnetic field measure in tesla (T) vectorl length of wire in the field20.3

Force on an Electric Current in a Magnetic FieldA tesla is also called a weber per meter squared

The units in cgs is called a Gauss

20.3

Magnetism20.4 Force on Electric Charge Moving in a Magnetic Field

Force on Electric Charge Moving in a Mag FieldThe equation can be determine by an analysis of the currentI is the amount of charge that passes a point in a given time

l can be defined asPutting those in the force equation

20.4

Force on Electric Charge Moving in a Mag FieldThe force is maximum when the charged particle moves perpendicular to the fieldZero when it moves parallel to the fieldThe angle is the angle between the velocity and the field The right hand rule will give you the correct direction for the force on a positive charge

20.4

Force on Electric Charge Moving in a Mag FieldIf we establish a uniform magnetic field and the charge moves perpendicular to the fieldIn our exampleField (fingers) is out of the slide-Velocity (thumb) is in the direction of the blue arrow-Force (palm) points toward middle (assume positive charge)The force is centripetal20.4

Force on Electric Charge Moving in a Mag FieldA very common type of problemThe electromagnetic force is the centripetal force

Charged particles from the sun, concentrate at the poles because of this called the Aurora Borealis 20.4

Magnetism20.5 Magnetic Field Due to a Long Straight Wire

Magnetic Field Due to a Long Straight WireAs discussed earlier, a current in a wire produces a magnetic fieldThis can be demonstrated by moving a compass around a current carrying wire.20.5

Magnetic Field Due to a Long Straight WireThe field around the wire is directly proportional to the current and inversely to the distance from the wire

m0 is called the permeability of free space20.5

Magnetism20.6 Force Between Two Parallel Wires

Force Between Two Parallel WiresAssuming that two wires are parallel to each other20.6

Magnetism20.9 Torque on a Current Loop; Magnetic Moment

Torque on a Current LoopElectric Motor

20.9

Magnetism20.10 Applications

ApplicationsGalvanometerCurrent flows throughthe wireProduces a magneticfieldThe magnetic field is attracted or repelled by the permanent magnetFound in analog voltmeters, ammeters, and ohmeters

20.10

ApplicationsElectric MotorCurrent flows throughthe wireProduces a magneticfieldThe magnetic field is attracted or repelled by the permanent magnet4. Brushes allow the current to switch

20.10

ApplicationsLoudspeakerCurrent from the ampflows through the wireProduces a magneticfieldThis pushes the coilaway, causing the cone to move outward4. Signal turns off, or switches, the cone moves back

20.10