Paramagnetism of Liquid Oxygen, 5G30.20

Topic and Concept:

• Magnetic Materials, 5G30. Paramagnetism and Diamagnetism

Location:

• Cabinet: (E&M)

• Bay: (A3)

• Shelf: #5

Abstract:

Liquid oxygen is trapped in a strong magnetic field until it evaporates.

Important Setup Notes:

• This demonstration requires a 24 hour notice.

• This demonstration requires about 1 L of liquid N2.

• It takes roughly 20 minutes to make enough liquid air for this demonstration.

Setup and Procedure:

1. Use clamp to attach water bottle to stand.
2. Fill the bottle with liquid nitrogen.
3. Pre-cool the small dewar by pouring in about 200 mL of liquid nitrogen.
4. Allow the nitrogen to stop boiling, and then pour it out.
5. Lower the bottle into the dewar. After 20 minutes, about 50 mL of liquid air will have condensed in the small dewar.
6. On the higher side of the steel channel relative to the magnets, pour the liquid air into the channel.
7. The oxygen component of the liquid air will be trapped in the magnetic field while the rest runs off.

Alternative Setup/Procedure:

1. Follow above setup/procedure replacing the stand w/clamp and water bottle with the copper cone and a ring stand.
2. To decrease the rate at which the liquid oxygen boils off, the aluminum channel and magnets can also be pre-cooled as part of step 3 above. See pictures below for example.

Cautions, Warnings, or Safety Concerns:

• Exercise great care when handling the liquid N2 - it can cause severe frost bite!

• NEVER put a cap on the container containing the liquid N2! Doing so would create a very DANGEROUS device that will explode sending shards of plastic into the audience.

• Liquid oxygen is EXTREMELY FLAMIBLE! Keep away from sparks or sources of open flame.

Discussion:

Air is a mixture of various gases. Roughly speaking, air is 78% N2, 21% O2, and 1% Ar while the other contributions from H2, C02, He, etc. are negligible. N2, Ar, He, H2 are all diamagnetic meaning that their respective magnetic dipole moments will anti-align themselves with the magnetic field causing a repulsion. 02 is the only component of our atmosphere that is paramagnetic meaning that the magnetic dipole moment is aligned with the magnetic field and so will be attracted. Thus, the trapped liquid will be pure oxygen. It will remain their until it gains energy from the hotter surrounding air and boils off.

Videos:

• The Paramagnetism of Liquid Oxygen, 5G30.20

• Lecture Demonstration's Youtube Channel

References:

• Paramagnetism - Wikipedia

• Liquid Oxygen - Wikipedia

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