Magnetic Field: Effects, Sources, and Forces

Slides:



Advertisements
Similar presentations
5.3 Magnetism IB Physics.
Advertisements

24-1 Magnets: permanent & temporary
Lecture Demos: E-40 Magnetic Fields of Permanent Magnets (6A-1) E-41 Oersted’s Experiment (6B-1) E-42 Force on a Moving Charge (6B-2) 6B-3 Magnetic Field.
Chapter 20 Magnetism.
 Electric generators  Television sets  Cathode-ray displays  Computer hard drives  Compass.
Chapter 22 Magnetism.
Magnetism Unit Notes 1 Grade 10 ST J. Kelly and A. Sanniti.
MAGNETISM SPH3U. Permanent Magnets A permanent magnet has two poles: North and South. Like poles repel. Unlike poles attract. These repulsive or attractive.
Ch20 Magnetism Durable.
Lecture Outline Chapter 19 College Physics, 7 th Edition Wilson / Buffa / Lou © 2010 Pearson Education, Inc.
MAGNETISM Adapted from Mr. Dellibovi
Magnetism Force of Mystery demo. Magnetism Standards Students know magnetic materials and electric currents (moving electric charges) are sources of magnetic.
Chapter 21 Magnetic Forces and Magnetic Fields Magnetic Fields The needle of a compass is permanent magnet that has a north magnetic pole (N) at.
Copyright © 2010 Pearson Education, Inc. Lecture Outline Chapter 22 Physics, 4 th Edition James S. Walker.
Physics 106 Lesson #20 Magnetism: Relay and Buzzer Dr. Andrew Tomasch 2405 Randall Lab
Magnetism Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons. Like.
Chapter 19 Magnetism. Magnets Poles of a magnet are the ends where objects are most strongly attracted Poles of a magnet are the ends where objects are.
Magnetism. Magnets ► A magnet has polarity - it has a north and a south pole; you cannot isolate the north or the south pole (there is no magnetic monopole)
 Natural Magnets  Magnetite, Fe 3 O 4 (an oxide of iron)  Ancient civilizations (Greek 590 BCE, Chinese 2600 BCE) realized that these stones would.
Forces: F net causes acceleration. Forces – act at distance F g – attractive btw masses. F e – attractive/repulsive between objects w net charge. F mag.
Concept Summary. Magnetic Poles  Magnetic forces are produced by magnetic poles.  Every magnet has both a North and South pole.  Like poles repel,
Electricity and Magnetism
Magnetism.
Magnetism. Magnets ► A magnet has polarity - it has a north and a south pole; you cannot isolate the north or the south pole (there is no magnetic monopole)
Electromagnetism.
Magnetism Unit Notes 1 Grade 10 ST. Magnetic Behaviour After watching the demo, what conclusions can you make about what you saw? _____________________________________.
Chapter 19 Magnetism. Fig. 19.1, p.587 Magnets Poles of a magnet are the ends where objects are most strongly attracted – Two poles, called north and.
Magnets and Magnetic Fields
Magnetism-Magnets Kailey Toro, Megan Ly, Chad Unrue, Michael Fairbanks Items 1-5 on the packet Science RULES.
Magnetism Unit 12. Magnets Magnet – a material in which the spinning electrons of its atom are aligned with one another Magnet – a material in which the.
Pearson Prentice Hall Physical Science: Concepts in Action Chapter 21 Magnetism.
Investigation 17B  Key Question: How are electricity and magnetism related? Electromagnets.
Magnetism. Magnets Poles of a magnet are the ends where objects are most strongly attracted – Two poles, called north and south Like poles repel each.
Chapter Twenty-Two: Electricity and Magnetism  22.1 Properties of Magnets  22.2 Electromagnets  22.3 Electric Motors.
Magnetism. Magnets  Poles of a magnet are the ends where objects are most strongly attracted Two poles, called north and south  Like poles repel each.
ELECTRICITY AND MAGNETISM
Magnetism Magnetism originates at the atomic level and is caused by moving electric charge Magnetic objects: Create magnetic fields around themselves.
Chapter 19 Preview Objectives Magnets Magnetic Domains Magnetic Fields
Magnetism and Electromagnetism
@ the end of the powerpoint
Magnetism Chapter LHS Physics Duke.
Chapter 36: Magnetism Purpose: To describe magnetic field around a permanent magnet. Objectives: Describe a magnetic poles Describe magnetic field. Magnetic.
Magnetism.
Magnets & Magnetic Fields
Physics Unit 6 - Magnetism
Magnetism and Electromagnets
Magnets Magnetism: property of some materials that allows them to give off an attractive or repulsive force. Magnet: a material that gives off an external.
Magnetic Fields Magnetic Forces
ELECTRICITY & MAGNETISM
Electromagnetism Continued
Chapter 19 Magnetism.
Section 1 Magnets and Magnetic Fields
Magnetism.
Chapter 14 Magnetism 11/28/2018.
Magnetism Force of Mystery demo.
Magnetic Fields.
Electricity & Magnetism How are electricity & magnetism related?
Why are some materials magnetic?
Unit 3.1 Magnetism – Part 1.
22.1 Properties of Magnets If a material is magnetic, it has the ability to exert forces on magnets or other magnetic materials nearby. A permanent magnet.
Magnetism.
Magnetism.
Magnetism Chapter 8.
Electromagnetism 1 (Chapter 14)
Electromagnets Key Question: Investigation 17B
Magnetism and Magnetic fields
Magnets Magnetism: property of some materials that allows them to give off an attractive or repulsive force. Magnet: a material that gives off an external.
Motion Field Current Physics 7: Magnetism and Electromagnetism
Magnetism.
Magnetic Field Measurement
Presentation transcript:

Magnetic Field: Effects, Sources, and Forces PES 1000 – Physics in Everyday Life

Two ‘flavors’ of magnetism Magnetism was discovered in antiquity. Naturally occurring magnets, lodestones, had two ends that would attract or repel other lodestones. Lodestones (if friction is eliminated) naturally orient themselves toward Earth’s poles. The ends of the lodestone are traditionally called North and South, depending on which geographic pole it pointed toward. You could paint the north-pointing end red and label it N. Likewise, you could label the south-pointing end S. The ends of the magnets are called ‘poles’, and they have ‘polarity’. You can test this with a compass. Experiments show that two like poles (North-North or South-South) repel, while North and South attract. A North-magnetic pole is South-seeking, and vice versa. Consequence: The Earth’s North geographic pole is actually a South magnetic pole, because the end of magnet labeled ‘North’ points toward it. Also, the magnetic poles of the Earth are not stationary, or are they exactly coincident with the geographic poles (which are fixed and clearly defined by the Earth’s spin axis), and the magnetic poles have actually swapped in the past!

Breaking a bar magnet into pieces If we break a bar magnet in half in order to have isolated North and South poles (monopoles)… …we find we can’t do this! We get two smaller magnets, each with its own N and S poles. If we keep going, breaking each of these magnets in half and so on… …we find that at the atomic level each iron atom has a N and S pole. There are no monopoles, only dipoles! In a permanent iron (ferrous) magnet, these atomic dipoles are aligned, so that the overall piece of iron has a net magnetic field. This is called ferro-magnetism. In a regular (non-magnetized) piece of iron, the dipoles point in random directions, and the net magnetic field is zero.

Magnetizing Iron & Magnetic Domains A microscopic view of a normal piece of iron shows that there are many tiny regions (domains) where the atomic magnets are aligned. The magnetic domains point in random directions, resulting in no net magnetic field in the iron. If an external magnetic field is applied, however, it forces the domains to slightly align with itself (temporarily), causing a net magnetic field in the iron and a resulting attraction. This is how a permanent magnet sticks to a non-magnetic refrigerator, for example. How to form a permanent magnet: Apply a very strong external field, leaving a residual magnetic field in the iron once the external field is removed. (Example: magnetic information storage) Allow the molten iron to cool in the presences of an external field. The domains will ‘freeze’ in an aligned configuration. (Example: natural lodestone cooled within the Earth’s magnetic field.) How to remove a permanent magnetic field: apply heat or physical vibration (also ‘degaussing’, which is the application of an oscillating field with decreasing magnitude).

Magnetic Fields Magnetic fields, like electric fields, have a size and direction. They are vectors. The variable used is usually 𝐵 . The SI unit for magnetic field strength is the Tesla (T). The magnetic di-polar field can be visualized much like we did for electric fields. We could make a grid around the magnet, place a compass at each point, and show the direction with an arrow and the strength with the brightness of the arrow. Another method is to connect all the arrows into field lines. Field lines always form closed loops. The loop may extend to infinity. They run through the magnet itself. The lines run from North to South. Lines are close together in regions of a strong magnetic field. Iron filings will align with the magnetic field lines, providing a visualization of them. Note the similarity of the electric and magnetic dipole fields. Magnetic Dipole Electric Dipole

Magnetic Force 𝐹 𝐵 𝑣 𝐵 𝑣 𝐹 𝐵 - Only moving charge experiences a force due to a magnetic field. A stationary charge is unaffected by a magnetic field. The force on the moving charge depends on: The size and sign of the charge The speed and direction the charge is moving relative to the field Magnetic field strength The direction of the force is perpendicular to both the field and the velocity of the moving charge. For positive charge, it follows the right-hand-rule, with index finger along the velocity, middle finger along the field, and thumb indicating the direction of the force. If the charge is negative, the force is in the opposite direction. Static charge generates (and experiences force from) only an electric field. Moving charge generates (and experiences force from) both magnetic and electric fields. 𝑣 + 𝐵 𝑣 - 𝐹 𝐵

Magnetic Field due to a current-carrying wire Imagine a long, straight current-carrying wire. Magnetic loops form around the wire. Right-hand-rule: Thumb is in direction of current, fingers curl in direction of magnetic field. Bend the wire into a loop of current-carrying wire. Magnetic loops join in the middle. Right-hand-rule: Fingers curl in direction of current, Thumb is in direction of magnetic field. Make a series of loops – magnetic fields join. Form a coil of wire (solenoid) This is an electro-magnet. You can switch it on and off. You can easily reverse it. B B I I

Magnet Simulation Link to simulation: https://phet.colorado.edu/en/simulation/legacy/magnets-and-electromagnets Things to do: On the ‘Bar Magnet’ tab: Observe how the compass North is attracted to magnet’s South, and vice versa. Click the ‘See Inside Magnet’ to see the magnetic loops passing through the bar magnet. Click the ‘See planet Earth’ to see the similarity of the Earth’s magnetic field to a bar magnet. On the ‘Electromagnet’ tab You can turn off the magnetic field, and you can reverse it. See how similar the electromagnet is to a bar magnet.

Conclusion Magnetism has two types of poles: a North and a South. North poles seek South poles and vice versa. Poles of the same type will repel each other. Di-pole magnetism is present in a magnet all the way down to the atomic level. There are no monopoles. In a ferrous (iron-like) material, tiny regions (domains) of atomic magnets will be aligned. Different domains may point different directions (no net magnetic field). If enough domains align, the iron may become temporarily or permanently magnetized. Magnetic forces on a moving charge follow the right-hand-rule. Moving charge forms a magnetic field around itself. Current carrying wires may be used to form a powerful magnetic field.