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New videos from Khan Academy 2021-07-21T16:07:24.161336
Actualizado: hace 1 hora 43 mins

Mutual inductance of two concentric coils

Lun, 2021-05-17 03:42
Let's calculate the mutual inductance of two concentric coils with the bigger coil having radius R1, and a smaller coil having radius R2, R2 being much smaller than R1.

Hysteresis & magnetic retention

Lun, 2021-05-17 03:42
The magnetic field inside a ferromagnet lags the vacuum field, and this lagging is called the hysteresis. Let's explore this hysteresis curve of ferromagnets.

Ferromagnetism & curie temperature

Lun, 2021-05-17 03:42
Ferromagnets are strongly attracted to magnets due to their magnetic domains. Magnetic domains are groups of atoms whose dipole moments are spontaneously aligned in the same direction. Above the Curie temperature, these magnetic domains break down and the material becomes a paramagnet.

What are inductors? (self-inductance)

Lun, 2021-05-17 03:42
Self-inductance is the tendency of a coil to resist changes in current in itself. Whenever current changes through a coil, they induce an EMF, which is proportional to the rate of change of current through the coil.

Velocity selector

Lun, 2021-05-17 03:42
To select charged particles of specific velocity, we can use the cross fields - perpendicular electric & magnetic fields. Particles whose velocity equals the ratio E/B would come out undeflected. This set up is called the velocity selector.

Magnetic dip & horizontal component of Earth's field

Lun, 2021-05-17 03:42
The angle made by the Earth's magnetic field with the horizontal, in the magnetic meridian, is called the dip. The dip is zero close to the equator and 90 degrees close to the magnetic poles. The dip angle is useful in calculating the horizontal and vertical components of the Earth's fields.

Ampere's circuital law (with examples)

Lun, 2021-05-17 03:42
Ampere's circuital law states that the closed-loop integral of B.dl (also called the 'circulation of magnetic field') always equals mu_not times the enclosed current.

Magnetic field due to two current loops: Numerical

Lun, 2021-05-17 03:42
Let's work out a numerical on calculating magnetic field due to two current loops. In the first case, these loops are coaxial and parallel. In the second case, these are concentric and perpendicular.

Eddy currents & their applications (& how to reduce them)

Lun, 2021-05-17 03:42
Eddy currents are current loops formed over conductor surfaces due to changing magnetic flux. They are useful in induction heating, levitating, electromagnetic damping, and electromagnetic braking. They can be minimized by adding slots in the conductor surface & laminating.

Bohr magneton (& gyromagnetic ratio)

Lun, 2021-05-17 03:42
Let's explore what the smallest magnetic moment an atom could have, using Bohr's theory. This minimum magnetic moment is called the Bohr magneton. Gyromagnetic ratio is the ratio of magnetic moment to angular momentum.

Mató Nájin/Standing Bear, Battle of Little Bighorn

Mié, 2021-05-05 14:03
Mató Nájin/Standing Bear (Minneconjou Lakota/Teton Sioux), Battle of Little Bighorn, c. 1920, pencil, ink, and watercolor on muslin, 91.4 × 268 cm, made in Pine Ridge Reservation, South Dakota, United States (The Metropolitan Museum of Art)

White Ogre Tihu (Katsina Figure)

Mié, 2021-05-05 14:03
Hopi, White Ogre Tihu (Katsina Figure), c. 1900, cottonwood, pigment, cotton cloth, tanned leather, and metal, made in Arizona, United States, 47 × 15.2 × 17.8 cm (The Metropolitan Museum of Art); speaker: Brian Vallo, Director, Indian Arts Research Center School for Advanced Research, Santa Fe, New Mexico 

Nampeyo, Polacca polychrome water jar

Mié, 2021-05-05 14:03
Nampeyo (Hopi-Tewa), Polacca Polychrome Water Jar, c. 1895–1900, clay and pigment, made in Arizona, U.S., 30.5 × 34.3 cm (The Metropolitan Museum of Art); speakers: Gaylord Torrence, Fred and Virginia Merrill Senior Curator of American Indian Art, The Nelson Atkins Museum of Art and Brian Vallo, Director, Indian Arts Research Center School for Advanced Research, Santa Fe, New Mexico

Anishinaabe shoulder bag

Mié, 2021-05-05 14:03
Anishinaabe, possibly Mississauga Ojibwa, Shoulder bag (missing strap), c. 1800, tanned leather, porcupine quills, dye, glass beads, silk ribbon, metal cones, and deer hair, Possibly made in Ontario, Canada; possibly made in Michigan, United States; possibly made in Wisconsin, United States, 30.5 × 22.9 cm (The Metropolitan Museum of Art)

Acoma polychrome water jar

Mié, 2021-05-05 14:03
Acoma polychrome water jar, c. 1890, from Acoma, clay and pigment, 25.1 x 29.8 cm (The Metropolitan Museum of Art); speaker: Brian Vallo, Director, Indian Arts Research Center School for Advanced Research, Santa Fe, New Mexico

Socorro black-on-white storage jar

Mié, 2021-05-05 13:44
Ancestral Pueblo, Socorro black-on-white storage jar, c. 1050–100, clay and pigment, made in New Mexico, United States, 38.1 × 43.2 cm (The Metropolitan Museum of Art); speaker: Brian Vallo, Director, Indian Arts Research Center School for Advanced Research, Santa Fe, New Mexico

Christus, A Goldsmith in his Shop

Mar, 2021-05-04 18:14
A conversation with Dr. Steven Zucker and Dr. Beth Harris in front of Petrus Christus, A Goldsmith in his Shop, 1449, oil on oak panel, 100.1 x 85.8 cm (The Metropolitan Museum of Art)

Pyramid of the Moon and Pyramid of the Sun, Teotihuacan

Mar, 2021-05-04 17:53
The Pyramid of the Moon and the Pyramid of the Sun, Teotihuacan, c. 1st century C.E., Mexico speakers: Dr. Lauren Kilroy-Ewbank and Dr. Beth Harris

Zisha “Ru Ding” teapot, Yixing ware

Mar, 2021-05-04 17:36
A conversation between Dr. Kristen Brennan and Dr. Steven Zucker in front of a Zisha "Ru Ding" teapot made by Yang Pengnian, with Chen Mansheng mark, Yixing ware, c. late 18th–early 19th century (Shanghai Museum of Art) Note: the work was created with slabs of clay and then worked on a wheel. The term "thrown" may be misleading.

K selected and r selected population growth strategies

Lun, 2021-05-03 17:17
K and r are two extremes for a range of population growth strategies, no one strategy is better or best. Identify the characteristics associated with K selected and r selected species. Volunteer here: https://www.khanacademy.org/contribute

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