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Grade the HWGrade the HW 105 Pts105 Pts

AP Physics AP Physics Lesson 48Lesson 48

Magnetic FieldsMagnetic Fields

Electricity and MagnetismElectricity and Magnetism

A match made in heaven?????A match made in heaven?????

Parts of a magnetParts of a magnet

North vs. SouthNorth vs. South Not the Civil WarNot the Civil War

North is attracted to SouthNorth is attracted to South The north end of a magnet aligns The north end of a magnet aligns

with the North Polewith the North Pole

MagnetsMagnets

Magnetic DomainsMagnetic Domains Aligned creates a magnetAligned creates a magnet Electron spinElectron spin

How to make a magnetHow to make a magnet How to make a magnet go badHow to make a magnet go bad

Magnetic FieldsMagnetic Fields

Force fields around magnetsForce fields around magnets Created by moving electric fields Created by moving electric fields

generated by a moving chargegenerated by a moving charge Symbol for magnetic field is BSymbol for magnetic field is B

Measured in units of Tesla (T)Measured in units of Tesla (T)

Drawing Magnetic FieldsDrawing Magnetic Fields

Drawing Magnetic FieldsDrawing Magnetic Fields

Drawing Magnetic FieldsDrawing Magnetic Fields

Use multiple lines to show uniform Use multiple lines to show uniform magnetic fieldsmagnetic fields

3D3D Into the page (x)Into the page (x) Out of the page (.)Out of the page (.)

Magnetic ForceMagnetic Force

Magnetic fields create forces on Magnetic fields create forces on moving chargesmoving charges Causes a change in directionCauses a change in direction Proportional to the size of chargeProportional to the size of charge Proportional to the speed of the chargeProportional to the speed of the charge Proportional to the size of the fieldProportional to the size of the field FFBB

Magnetic ForceMagnetic Force

FFBB = qvBsin = qvBsinθθ A charge moving at an angle to the field A charge moving at an angle to the field

experiences less of a forceexperiences less of a force Helical MotionHelical Motion

Right Hand RuleRight Hand Rule

Helps us predict the direction of the Helps us predict the direction of the forceforce Predicts which way the charge will be Predicts which way the charge will be

deflecteddeflected

RHRRHR

Example IExample I

A proton moving from left to right A proton moving from left to right with a velocity of 305m/s enters a with a velocity of 305m/s enters a magnetic field that is perpendicular magnetic field that is perpendicular to the plane of the paper (coming out to the plane of the paper (coming out of the page). The strength of the of the page). The strength of the field is 44T. Find the magnitude and field is 44T. Find the magnitude and direction of the force on the proton direction of the force on the proton as it enters the field. as it enters the field.

AnswerAnswer

2.1x102.1x10-15-15N down. N down.

Example IIExample II

An electron travels at 2.0x10An electron travels at 2.0x1077m/s to m/s to the right at it enters a 0.010T magnetic the right at it enters a 0.010T magnetic field directed into the page. A) field directed into the page. A) Determine the magnitude of the force Determine the magnitude of the force acting on the charge. B) Determine acting on the charge. B) Determine the direction of the force. C) Sketch the direction of the force. C) Sketch the magnetic field and path the charge the magnetic field and path the charge takes. Describe the path as moving takes. Describe the path as moving either clockwise or counterclockwise. either clockwise or counterclockwise.

AnswerAnswer

3.2x103.2x10-14-14N down and clockwise. N down and clockwise.

Example IIIExample III

A charge of 8.1x10A charge of 8.1x10-9-9C enters a C enters a magnetic field with a speed of magnetic field with a speed of 2200m/s at an angle of -30°. The 2200m/s at an angle of -30°. The 4.0T magnetic field is moving from 4.0T magnetic field is moving from left to right. Determine the left to right. Determine the magnitude of the force the field magnitude of the force the field exerts on the charge. exerts on the charge.

AnswerAnswer

3.6x103.6x10-5-5N. N.