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Unit 5: Magnetism. Physics B. Bell Work. Using the items at your desk, make as many observations as possible about the properties of magnets. Shape of the Magnetic Field. http:// phet.colorado.edu/en/simulation/magnets-and-electromagnets. Properties of Magnets.
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Unit 5: Magnetism Physics B
Bell Work Using the items at your desk, make as many observations as possible about the properties of magnets.
Shape of the Magnetic Field http://phet.colorado.edu/en/simulation/magnets-and-electromagnets
Properties of Magnets • If you break a magnet into pieces what happens? • If this happens, what does this mean about ‘monopoles’? But, what causes magnetism?
1. Properties of Particles with charge Does this mean all matter is magnetic?
2. The Atom Ferromagnetic / Anti-ferromagnetic
4. Domains How do we know the moon use to have a magnetic field?
Bell Work Given this crystal of Cadmium (Cd) and Titanium (Ti), determine if the structure isferro or anti-ferromagnetic at theatomic and crystal levels.
https://www.youtube.com/watch?v=1TKSfAkWWN0 Currents create magnetic fields! • Right-hand-rule: Put your thumb in the direction of the current, and your fingers wrap around in the direction of the magnetic field.
Practice I I I
B = magnetic field µ = permeability of free space n = number of turns I = current
Magnetic Field App & Gauge Bozons • http://www.falstad.com/vector3dm/
The Tesla! https://www.youtube.com/watch?v=pPnGvjmIgZA
Quantifying Magnetism A charge traveling through a magnetic field experiences a force… Magnetic Force [N] = Charge [C] * velocity of charge [m/s] * magnetic field strength [T]* sine of the angle between v & B
Practice! • A proton moving east experiences a force of 8.8 x 1019 N upward due to the Earth’s magnetic field. At this location, the field has a magnitude of 5.5 x 10-5 T to the north. Find the velocity of the particle.
A charge moving through a magnetic field follows a circular path…
Another Thought: B • A wire, with a charge Q lays in a magnetic field pointed out of the page… • If the wire is physically moved to the left… • The force is in the _______ direction. • What does this mean? v l Q
Since there’s a force…. We can analyze the Work done on the charge… So, the work done on a charge is… What are the units on this quantity?
EMF: Electromotive Force The force on charges due to a magnetic field, that act like a potential difference, causing currents in wires.
New Problem • A wire, with 6 Ω of resistance, and 12 m of length, sits in a magnetic field of 2 T in the same position as the previous example. Calculate the magnitude of the current. • Note: Recall Ohm’s Law
Bell Work • Given the setup to the left, does a current flow through the wire? • Given the initial conditions: - v = 5 m/s - length = 5 m - the work done on each charge due the magnetic field is 9 V Determine the strength of the magnetic field.
Magnetic Force on a current carrying conductor… Magnetic Force [N] = Magnetic Field [T] * Current [A] * length of conductor [m]
Practice • A wire 36 m long carries a current of 22 A from east to west. If the magnetic force on the wire due to Earth’s magnetic field is downward (towards Earth) and has a magnitude of 0.04 N, find the magnitude and direction of the magnetic field at this location.
In the event of two wires, creating their own magnetic fields, and exposing each other to those fields…. I I
Two parallel wires • Currents flowing in the same direction. Will the wires attract or repel? • Currents flowing in the opposite direction. Will the wires attract or repel?
Changing Magnetic Fields generate currents… Currents can be created by changing magnetic fields, in an attempt to RESIST the change. The change occurs by changing the FLUX of the magnetic field through a loop of a conducting material. What are the units of magnetic flux? https://www.youtube.com/watch?v=txmKr69jGBk https://www.youtube.com/watch?v=NqdOyxJZj0U
Magnetic Induction Electromotive Force = - # of loops x the change in the Magnetic Flux over some time interval
So changes to flux occur when: • The area the field goes through changes. • An area is exposed to a magnetic field or magnetic field strength changes. • The angle the loops is in the magnetic field changes.
