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New videos from Khan Academy 2020-10-23T18:27:15.000000
Mis à jour : il y a 2 heures 11 min


ven, 2020-10-23 18:27
A common method of making a solution of a given concentration involves taking a more concentration solution and adding water until the desired concentration is reached. This process is known as dilution. We can relate the concentrations and volumes before and after a dilution using the following equation: M₁V₁ = M₂V₂ where M₁ and V₁ represent the molarity and volume of the initial concentrated solution and M₂ and V₂ represent the molarity and volume of the final diluted solution.

Representing solutions using particulate models

ven, 2020-10-23 18:27
A solution is a homogeneous mixture composed of two or more pure substances. In this video, we'll learn how to represent the relative concentrations of the substances in a solution as well as the interactions between them using a particulate model.


ven, 2020-10-23 18:27
The most common way to express solution concentration is molarity (M), which is defined as the amount of solute in moles divided by the volume of solution in liters: M = moles of solute/liters of solution. A solution that is 1.00 molar (written 1.00 M) contains 1.00 mole of solute for every liter of solution.

Types of mixtures

ven, 2020-10-23 18:27
A mixture is composed of one or more pure substances in varying composition. There are two types of mixtures: heterogeneous and homogeneous. Heterogeneous mixtures have visually distinguishable components, while homogeneous mixtures appear uniform throughout. The most common type of homogenous mixture is a solution, which can be a solid, liquid, or gas.

Population diversity and resilience

jeu, 2020-10-22 15:50
The higher the genetic diversity in a population, the more resilient the population is to environmental change.

Real gases: Deviations from ideal behavior

jeu, 2020-10-22 00:02
In this video, we examine the conditions under which real gases are most likely to deviate from ideal behavior: low temperatures and high pressures (small volumes). At low temperatures, attractions between gas particles cause the particles to collide less often with the container walls, resulting in a pressure lower than the ideal gas value. At high pressures (small volumes), finite particle volumes lower the actual volume available to the gas particles, resulting in a pressure higher than the ideal gas value.

The kinetic molecular theory of gases

jeu, 2020-10-22 00:02
The kinetic molecular theory (KMT) describes the behavior of ideal gases at the particle level. The five main postulates of the KMT are as follows: (1) the particles in a gas are in constant, random motion, (2) the combined volume of the particles is negligible, (3) the particles exert no forces on one another, (4) any collisions between the particles are completely elastic, and (5) the average kinetic energy of the particles is proportional to the temperature in kelvins.

Kinetic molecular theory and the gas laws

jeu, 2020-10-22 00:02
The kinetic molecular theory (KMT) can be used to explain the macroscopic behavior of ideal gases. In this video, we'll see how the KMT accounts for the properties of gases as described by the various gas laws (Boyle's law, Gay-Lussac's law, Charles's law, Avogadro's law, and Dalton's law of partial pressures).

Wang Lü among the peaks, Ming paintings of Mt. Hua

mer, 2020-10-21 16:25
Wang Lü, Landscapes of Mount Hua (Huashan), album leaves, 1384 (Ming Dynasty, China), ink on paper (Shanghai Museum) Speakers: Dr. Kristen Loring Brennan and Dr. Steven Zucker

Treasure from Spain: lusterware as luxury

mer, 2020-10-21 15:50
A conversation between Dr. Lauren Kilroy-Ewbank and Dr. Steven Zucker in front of a lusterware dish, second half of the 15th century, tin-glazed and luster-painted earthenware, made in Valencia, Spain, 38.4 cm diameter (The Metropolitan Museum of Art)

A Renaissance miniature in wood and feathers

mer, 2020-10-21 15:50
A conversation between Dr. Lauren Kilroy-Ewbank and Dr. Beth Harris in front of a pendant triptych with scenes of the Passion, 16th century, boxwood, feathers, gold, enamel, 4.4 x 4.4 cm (The Metropolitan Museum of Art)

A failed experiment: Medici porcelain

mer, 2020-10-21 15:50
Ewer (brocca), c. 1575–87, soft-paste porcelain, decorated in underglaze blue, 20.3 x 10.8 x 12.4 cm (The Metropolitan Museum of Art). Speakers: Dr. Lauren Kilroy-Ewbank and Dr. Steven Zucker In the 1560s, the Grand Duke of Florence, Francesco I de’ Medici, started a ceramic workshop in Florence with the intent to produce true porcelain (Chinese porcelain). After more than 10 years of experimentation, the workshop was able to make a type of porcelain that we now call soft-paste porcelain, which is considered an inferior type of porcelain. The experiment had failed to replicate true porcelain, yet Francesco was immensely proud of his workshop’s achievements. Even if it was not of the same quality as true Chinese porcelain, the Medici porcelain was still a significant achievement in its own right. Francesco added the Medici mark (an F and a dome) to his porcelain, which he often gave as diplomatic gifts. These ceramics were very expensive to produce because they required so much wood to fire the kilns. They also represent Francesco’s interest in alchemy, the attempt to transform one substance into another. Many of the surviving Medici porcelain examples demonstrate how artists in Florence adapted and transformed the decorations found on Chinese porcelain exported from Jingdezhen and Iznik ceramics from the Ottoman Empire. Medici porcelain also often includes grotesques, which are decorative elements that had become popular in the Renaissance era with the rediscovery of the ancient Roman Domus Aurea (a palace of the Roman emperor Nero). Today, just over 50 examples of Medici porcelain survive. Terms and key ideas: Medici porcelain factory Francesco I de’ Medici soft-paste porcelain kaolin alchemy Chinese porcelain Iznik ceramics transculturalism

The Arena Chapel (and Giotto's frescos) in virtual reality

mer, 2020-10-21 15:50
Take a guided virtual tour of the Scrovegni (Arena) Chapel, in Padova, Italy — thanks to Matthew Brennan. 360-degree video allows you to look around the interior freely, and provides a new perspective on this masterpiece of Italian Renaissance art. See the frescoes up-close and at eye-level, as if you were floating right in front of them, thanks to a new approach developed by Mirror Stage Studio. Narration by SmartHistory: Video production by Mirror Stage: This video makes use of imagery available in the public domain, as well as provided by Smarthistory.

A theatre in wood: the Sopetrán Lamentation

mer, 2020-10-21 15:29
A conversation between Dr. Lauren Kilroy-Ewbank and Dr. Beth Harris in front of the Sopetrán Lamentation, c. 1480, painted and gilded wood, 210.8 x 123.2 x 34.3 cm, originally part of an altarpiece at the Benedictine monastery at Sopetrán, Castile-La Mancha, Spain (The Cloisters)

A Jewish house in Damascus, Bayt Farhi

mer, 2020-10-21 15:12
Bayt Farhi, a Sephardic palace in Ottoman Damascus, begun c. 1780 an ARCHES video Speakers: Dr. Elizabeth Macaulay-Lewis and Dr. Steven Zucker

Types of studies

mer, 2020-09-30 17:16
We can distinguish between experiments and observational studies, and further describe types of observational studies: retrospective, prospective, and sample surveys.

Influential points in regression

mar, 2020-09-29 18:44
Outliers and high-leverage points can be influential to different measurements in least-squares regression like the slope, y-intercept, and correlation coefficient (r).

Potentiometer - calculating internal resistance of a cell

mar, 2020-09-29 07:38
To calculate internal resistance, we use a potentiometer to first calculate the voltage across the battery, with no current through it. Then we attach a resistor in parallel to the battery and recalculate the voltage across it. Since the current flows, this time the balancing length is smaller. Using the battery equation, we calculate the internal resistance.

Field due to infinite plane of charge (Gauss law application)

mar, 2020-09-29 07:38
Let's use Gauss law to calculate the electric field due to an infinite line of charge, without integrals.

Conversion of galvanometer into ammeter

mar, 2020-09-29 07:38
To convert a moving coil galvanometer to an ammeter, we add a low shunt resistance, but why? The shunt resistance carries the excess current, ensuring the right amount of current through the galvanometer.