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New videos from Khan Academy 2020-02-16T00:46:05.285495
Aggiornato: 1 ora 6 min fa

Magnetic effects of electric current: CBSE board practice

Sab, 2019-12-28 14:01
Prepare for class 10 CBSE exam for the chapter Magnetic Effects by recalling the concepts of hand rules, generators, and motors.

Electricity class 10 numerical: CBSE board practice

Sab, 2019-12-28 14:01
Prepare for class 10 CBSE exam for the chapter Electricity by revising difficult board-type numerical questions.

Beyond the Great Wave — Hokusai at 90

Mer, 2019-12-18 22:59
The great Japanese master Hokusai expresses a sense of a life well-lived in these two paintings — of a woodcutter and a fisherman. A conversation with Dr. Frank Feltens, The Japan Foundation Assistant Curator of Japanese Art, Freer Gallery of Art and Dr. Beth Harris, in front of Katsushika Hokusai, Fisherman, 1849, ink and color on silk, 113 x 39.6 cm and Woodcutter, 1849, ink and color on silk, 113.6 × 39.6 cm (Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution, gift of Charles Lang Freer in 1920, F1904.181 and 1904.182)

Queen or goddess?

Mer, 2019-12-18 18:34
Queen Sembiyan Mahadevi as the Goddess Parvati, Chola Dynasty (reign of Queen Sembiyan Mahadevi), 10th century, bronze, 107.3 x 33.4 x 25.7 cm (Purchase — Charles Lang Freer Endowment, Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution, F1929.84) Speakers: Dr. Emma Natalya Stein, Curatorial Fellow for Southeast Asian Art, Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution

Covalent bonds

Dom, 2019-12-15 22:13
Covalent bonds involve the sharing of electron pairs between atoms. Electron pairs shared between atoms of equal or very similar electronegativity constitute a nonpolar covalent bond (e.g., H–H or C–H), while electrons shared between atoms of unequal electronegativity constitute a polar covalent bond (e.g., H–O).

Metallic bonds

Dom, 2019-12-15 22:13
Metallic bonds result from the electrostatic attraction between metal cations and delocalized electrons. The nature of metallic bonding accounts for many of the physical properties of metals, such as conductivity and malleability.

Ionic bonds

Dom, 2019-12-15 22:13
Ionic bonds result from the electrostatic attraction between oppositely charged ions, which form when valence electrons are transferred from one atom to another.

Valence electrons and ionic compounds

Dom, 2019-12-15 22:13
When forming ions, elements typically gain or lose the minimum number of electrons necessary to achieve a full octet. For example, fluorine has seven valence electrons, so it is most likely to gain one electron to form an ion with a 1- charge. We can use this method to predict the charges of ions in ionic compounds.

Introduction to electron configurations

Sab, 2019-12-14 01:23
Electron configurations describe where electrons are located around the nucleus of an atom. For example, the electron configuration of lithium, 1s²2s¹, tells us that lithium has two electrons in the 1s subshell and one electron in the 2s subshell.

CBSE board practice: Lenses & mirrors

Ven, 2019-12-13 11:25
Let's practice recalling important aspects of mirrors & lenses

Worked example: Calculating mass percent

Ven, 2019-12-13 00:02
To calculate the mass percent of an element in a compound, we divide the mass of the element in 1 mole of the compound by the compound's molar mass and multiply the result by 100.

Worked example: Determining an empirical formula from combustion data

Gio, 2019-12-12 00:57
In combustion analysis, an organic compound containing some combination of the elements C, H, N, and S is combusted, and the masses of the combustion products are recorded. From this information, we can calculate the empirical formula of the original compound.

Worked example: Calculating molar mass and number of moles

Mer, 2019-12-11 17:10
The molar mass of a substance is the mass in grams of 1 mole of the substance. As shown in this video, we can obtain a substance's molar mass by summing the molar masses of its component atoms. We can then use the calculated molar mass to convert between mass and number of moles of the substance.

Average atomic mass

Mer, 2019-12-11 17:10
The average atomic mass (sometimes called atomic weight) of an element is the weighted average mass of the atoms in a naturally occurring sample of the element. Average masses are generally expressed in unified atomic mass units (u), where 1 u is equal to exactly one-twelfth the mass of a neutral atom of carbon-12.

Key features of graphs — Harder example

Mer, 2019-12-11 02:03
Watch Sal work through a harder Key features of graphs problem

Percents — Harder example

Mer, 2019-12-11 02:03
Watch Sal work through a harder Percents problem.

Bada Shanren, Lotus and Ducks

Mer, 2019-12-11 01:41
Bada Shanren 八大山人 (朱耷), Lotus and Ducks (colophon by Wu Changshuo 吳昌碩), c. 1696 (Qing dynasty), ink on paper (hanging scroll), image 185 x 95.8 cm (Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution). Speakers: Stephen D. Allee, Associate Curator for Chinese Painting and Calligraphy, Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution and Steven Zucker

Alexander, the Mongols, and the great epic of Iran

Mar, 2019-12-10 20:17
The Bier of Iskandar (Alexander the Great), folio from the Great Mongol Shahnama (Il-Khanid dynasty, Tabriz, Iran), c. 1330, ink, opaque watercolor and gold on paper, 57.6 x 39.7 cm (Freer Gallery of Art, Smithsonian Institution, purchase — Charles Lang Freer Endowment, F1938.3) This video focuses on one particular painting within one particular 14th century manuscript now commonly called the Great Mongol Shahnama. This is only one of many versions of the Shanama, the great epic of Iran. Speakers: Dr. Massumeh Farhad, Chief Curator and The Ebrahimi Family Curator of Persian, Arab, and Turkish Art, Freer Gallery of Art and Arthur M. Sackler Gallery, Smithsonian Institution and Dr. Steven Zucker

Red so rare it was lost to time —a ritual Ming dish

Mar, 2019-12-10 18:12
A conversation with Jan Stuart, Melvin R. Seiden Curator of Chinese Art, Freer Gallery of Art and Arthur M. Sackler Gallery and Steven Zucker in front of Dish with copper-red glaze, Ming dynasty, porcelain with copper-red glaze, on the base, a six-character cobalt-oxide (blue reign mark in a double circle under colorless glaze, c. 1426-35, 4.6 x 22 cm (Freer Gallery of Art, Smithsonian Institution, Washington D.C. Purchase — Charles Lang Freer Endowment and Friends of the Freer and Sackler Galleries, F2015.2a-b)

Causation from 1980-2020

Sab, 2019-12-07 01:34
How did events in the years after 1980 affect national identity in the United States? In this video, Kim discusses changes in US foreign policy, economics, and politics, attempting to place the developments of this era into a broader historical context.

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