Magnetism

What is a magnet?

An object that attracts iron containing objectsHas two poles

North and southLaw of poles- Like poles repel while opposite attract

Clicker Question

A bar magnet is divided into two pieces. Which of the following statements is true?A) the bar magnet is demagnetizedB) the magnetic field of each separated piece becomes strongerC)the magnetic poles are separatedD) two new bar magnets are created

What are magnetic fields?

A region in which the magnetic force can be detectedThe magnetic fields go from the north pole to the south pole

Clicker Question

Magnetic Field Diagram # 3

Magnetic Field Lines

Also called flux linesNever cross each otherThe closer they are the stronger the field

Earth’s Magnetic Field

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Earth’s Magnetic Field

The north pole is actually the south pole of Earth’s magnet!The magnetic south pole is near the geographic North pole and vice versa.This is why compasses point to the south pole of a magnet in a magnetic field but we say that compasses point north

Earth’s Magnetic Field

Clicker QuestionWhich of the following statements is most correct?

A. The north pole of a freely rotating magnet points north because the magnetic pole near the geographic North Pole is like the north pole of a magnet.B. The north pole of a freely rotating magnet points north because the magnetic pole near the geographic North Pole is like the south pole of a magnet.C. The north pole of a freely rotating magnet points south because the magnetic pole near the geographic South Pole is like the north pole of a magnet.D. The north pole of a freely rotating magnet points south because the magnetic pole near the geographic South Pole is like the south pole of a magnet.

What is magnetism caused byCaused by moving chargesAny time a charge moves (current) a magnetic field is createdSo….electric current can create magnetic fieldsMagnetic force is created by two magnetic fields occupying the same space

What are magnets?Electrons have a spin, so there are moving charges in atomsMost atoms’ electrons are paired up though and spinning in opposite directions, so the fields that are generated are cancelledWhen the electrons are not paired up then the fields are not cancelled These materials can be magnetic

Electric Fields Versus Magnetic Fields

Electric FieldsCaused from a positive or negative chargesCharges can be moving or stationaryFields move from positive to negativeCan be caused by a single charge

Magnetic FieldsCaused from moving chargesField lines move from north to south poleAlways caused from two poles

Magnetic Fields and CurrentWhen there is an electric current a magnetic field (B-field) is created around itUse the right hand ruleThumb will point in the direction of the currentFingers will curl in the direction of the B field

Clicker Question

An electric current flows into the page. What is the direction of the magnetic field?A) to the bottom of the pageB)to the top of the pageC)ClockwiseD)counter-clockwiseE) to the right

Clicker Question

A current is flowing to the right, in what direction will the magnetic field be?A)Into the pageB)out of the pageC)clockwiseD)counter-clockwiseE)to the left

Magnetic Fields in Solenoids

Solenoid is a long helically wound coil of wireSolenoids produce a strong magnetic field by combining several loopsMore loops= stronger magnetic field

Magnetic Force

A charge moving through a magnetic field experiences a magnetic force The force is proportional to the

ChargeVelocityMagnetic field

Magnetic ForceAlternative Right Hand RuleDirection of your palm=magnetic forceFingers= magnetic field linesThumb=velocity of particleWhen drawing An X= into the pageA = out of the page

Clicker Question

A positive charge enters a uniform magnetic field as shown. What is the direction of the magnetic force? Velocity is pointed up and fields pointed into page.A) out of the pageB) into the pageC) downwardsD) to the rightE) to the left

Clicker Question

A positive charge enters a uniform magnetic field. What is the direction of the magnetic force? The velocity is to the right and the magnetic field is into the page.A) out of the pageB) into the pageC) DownwardsD) upwardsE) to the left

Multiple WiresIf two wires were parallel to each other and the current was in the same direction, they would attractIf the current is in the opposite direction they would repel

Electromagnetic InductionChanging magnetic fields creates a potential difference (or EMF) in a conductorSo.. Magnetic fields can create currentsThis allows physical work to create electrical energy

Transformers

Power that is generated for transmission (for homes and buildings) is ramped up (about 100000 V) when it arrives at your home you need it at a lower level (120V)To convert voltage to a higher or lower value we use a transformer

Transformer

Consists of a primary coil and a secondary coilThe current flows through the primary magnetic fieldMagnetic field current in secondary coilWe use alternating current for thisWhen a transformer increases voltage it is called a step up (more secondary coils)When a transformer decrease voltage it is called a step down (more primary coils)