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New videos from Khan Academy 2021-06-22T17:30:48.000000
Actualizado: hace 1 hora 48 mins

“Protractor, Variation I” by Frank Stella

Mar, 2021-06-22 17:30
“Protractor, Variation I” by Frank Stella is an acrylic and graphite painting on canvas at the Pérez Art Museum Miami. Created in 1969, the painting is 16 feet wide by 8 feet tall, and is composed of rhythmic bands of color in the shape of a protractor. This work is one of nearly 100 paintings in Stella’s Protractor series. Discover more reasons why this is a masterpiece with Franklin Sirmans, Director of the Pérez Art Museum Miami.

Van Gogh, The Starry Night

Lun, 2021-06-21 15:48
Vincent van Gogh, The Starry Night, 1889 (June, Saint Rémy), oil on canvas, 73.7 x 92.1 cm (The Museum of Modern Art) Speakers: Dr. Beth Harris and Dr. Steven Zucker

Public art, politics, and the banishing of Civic Virtue

Vie, 2021-06-11 18:01
Frederick MacMonnies (sculptor), Thomas Hastings (architect), Piccirilli Brothers (carvers), Civic Virtue Triumphant Over Unrighteousness, 1922, marble, more than 17 feet high (originally City Hall Park, Manhattan, then Queens Borough Hall, now Green-Wood Cemetery, Brooklyn but without fountain basins) Speakers: Dr. Michele Bogart and Dr. Steven Zucker

Vertis Hayes, The Lynchers

Vie, 2021-06-11 17:09
Warning: this video contains graphic scenes of racial violence. Vertis Hayes, The Lynchers, 1930s, oil on canvas, 19-1/2 x 15-1/4 inches (Georgia Museum of Art, Athens) Speakers: Dr. Shawnya Harris, Larry D. and Brenda A. Thompson Curator of African American and African Diasporic Art at the Georgia Museum of Art and Dr. Beth Harris

Josiah McElheny on Horace Pippin

Vie, 2021-06-11 17:09
Josiah McElheny on Horace Pippin "Every human being has the potential of great insight." Video by The Metropolitan Museum of Art

The convento of Acolman

Vie, 2021-06-11 16:45
A conversation between Dr. Lauren Kilroy-Ewbank and Dr. Steven Zucker in the atrium of the ex-convento, San Agustín de Acolman, Acolman de Nezahualcóyotl, Mexico

The Damascus Room at The Metropolitan Museum of Art

Mar, 2021-06-08 19:07
The Damascus Room at The Metropolitan Museum of Art is a period room dating back to 1707 in Damascus, Syria, which was part of the Ottoman Empire. The luxurious space was a reception room, likely for an affluent family to host visitors. The opulent décor and poetic inscriptions were designed to make the space feel like a retreat from the bustling commercial center located on the Silk Road and the route to Mecca. Explore the masterpiece with Max Hollein, Marina Kellen French Director of the Metropolitan Museum of Art in New York. By Bank of America.

“Bodhisattva of Compassion Seated in Royal Ease”

Mar, 2021-06-08 18:43
“Bodhisattva of Compassion Seated in Royal Ease” at the Denver Art Museum was created in 10ᵗʰ century China. The 17-inch-tall sculpture depicts the bodhisattva Guanyin sitting serenely on a lotus throne, gazing down as if listening intently to its devotees. Guanyin’s name means “the one who always hears.” Discover what makes this 1,000-year-old sculpture a masterpiece with Christoph Heinrich, Frederick and Jan Mayer Director of the Denver Art Museum. Video by Bank of America.

Why current lags voltage in inductors (logic)

Jue, 2021-06-03 11:01
Let's explore why the current through a pure inductor lags the voltage by 90 degrees.

What is power factor? (Power in AC circuits)

Jue, 2021-06-03 11:01
The power factor represents the fraction of the available power (also called apparent power) that is consumed (also called the true power) by the circuit. Low power factors cause higher heating losses in transmission lines. Let's explore this in more detail.

Phasor diagram (& its applications)

Jue, 2021-06-03 11:01
Phasors are rotating vectors having the length equal to the peak value of oscillations, and the angular speed equal to the angular frequency of the oscillations. They are helpful in depicting the phase relationships between two or more oscillations. They are also a useful tool to add/subtract oscillations.

AC voltage across a capacitor (derivation)

Jue, 2021-06-03 11:01
When an alternating voltage is applied across a capacitor, the current leads the voltage by a phase angle of 90 degrees. This means the current oscillates a quarter of the cycle ahead of the voltage. Let's derive an expression for this current.

Why current leads voltage in a capacitor (logic)

Jue, 2021-06-03 11:01
Let's explore why the alternating current in a capacitor leads the voltage across it by a quarter of a cycle.

Reactance, resistance, & impedance (what's the difference?)

Jue, 2021-06-03 11:01
The opposition offered by capacitors and inductors to alternating currents is called reactance. Reactance values depend on frequency while resistances don't. Reactances resist currents without dissipating power, unlike resistors. Inductive reactance increases with frequency and inductance. Capacitive reactance decreases with frequency and capacitance. Impedance represents total opposition provided by reactance and resistance.

AC voltage across pure inductor (derivation)

Jue, 2021-06-03 11:01
When an alternating voltage is applied to a purely inductive circuit, the current lags the voltage by 90 degrees. Let's calculate the expression for this current.

Sine wave RMS value - derivation (without calculus)

Jue, 2021-06-03 11:01
To calculate the RMS value of any function, we first square it, then find the mean value over some time period, and finally take the square root of it. Since sine and sin squared functions are both symmetrical in their centers, we can calculate their mean value without using calculus. Let's explore how.

What is RMS value? (& why should we care?)

Jue, 2021-06-03 11:01
RMS or root mean square current/voltage of the alternating current/voltage represents the d.c. current/voltage that dissipates the same amount of power as the average power dissipated by the alternating current/voltage. For sinusoidal oscillations, the RMS value equals peak value divided by the square root of 2.

AC voltage applied to resistors

Jue, 2021-06-03 11:01
When an alternating voltage is applied to a purely resistive circuit, the current can be calculated using Ohm's law. We find the current also alternates in phase with the voltage.

Discovering Sacred Texts: Hinduism

Vie, 2021-05-28 17:16
Discover the diversity and richness of Hinduism, from the ancient oral tradition of the Vedic texts, the colourful stories of the Ramayana and Mahabharata, and the ways in which gods and goddesses are worshipped today. From the British Library.

Introduction to Khan Academy (for students) (Hindi)

Mié, 2021-05-26 22:22
You can share this video directly with your students.

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