Unit 5: Magnetism

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# Unit 5: Magnetism - PowerPoint PPT Presentation

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

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.

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.

B = magnetic field

µ = permeability of free space

n = number of turns

I = current

Magnetic Field App & Gauge Bozons

The Tesla!

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.
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?