New videos from Khan Academy 2022-01-19T20:39:57.020788
Atualizado: 15 minutos 2 segundos atrás
Miniature furniture and figurines from the Tomb of Pan Yongcheng, 16th–17th centuries (Ming dynasty), local beech wood and metal, excavated in Shanghai in 1960 (Shanghai Museum) Speakers: Dr. Kristen Brennan and Dr. Beth Harris
Michelle L. Browder (with Deborah Shedrick and a team of artists), Mothers of Gynecology, 2021, found metal objects and other media, roughly 15 feet high (Mission for More Up campus Montgomery, Alabama, © Michelle L. Browder) speakers: Michelle Browder and Beth Harris
Kehinde Wiley, Rumors of War, 2019, patinated bronze with stone pedestal, overall: 27’4 7/8” x 25’5 7/8” x 15’9” 5/8” (Virginia Museum of Fine Arts) © Kehinde Wiley. A conversation with Valerie Cassel Oliver, Sydney and Frances Lewis Family Curator of Modern and Contemporary Art, Virginia Museum of Fine Arts, and Beth Harris.
Let's calculate the charge enclosed by a cylinder placed in a non-uniform electric field. Since a cylinder is a closed surface, we can use Gauss's law to help us.
Let's explore how and why we treat area as a vector. The direction of area vector is always perpendicular to it. For open surfaces, we have to arbitrarily choose between two perpendiculars, but for closed surfaces, we choose the outward direction as our standard. This helps us define the flux to be the dot product of electric field and the area.
Let's compare and contrast the electric force and the magnetic force, the Lorentz force, properties.
Let's explore how to calculate capacitance of a capacitor when it's partially filled with a dielectric.
Let's explore how to calculate the cyclotron frequency.
Let's derive an expression for the energy density of the electric field, by using the energy stored in a parallel plate capacitor.
Let's explore how the strength of electric & magnetic fields affect the energy at which the particles exit the cyclotron. Spoilers - The effects are counter intuitive!
Let's solve a numerical and see how to figure out where the null point is. The null point is where the net electric fields due to all charges add up to be zero.
Q1 A proton and a helium nucleus is shot into a uniform magnetic field, at right angles to the field, with the same speed. Find the ratio of their radii. Q2 Two protons are shot into a uniform magnetic field, at right angles to the field, with their velocities in the ratio 1:2. Find the ratio of their time periods.
Let's explore the working principle of cyclotrons
Beauford Delaney, Marian Anderson, 1965, oil on canvas, 160.02 x 130.81 cm (Virginia Museum of Fine Arts, Richmond). A conversation with Dr. Shawnya Harris, the Larry D. and Brenda A. Thompson Curator of African American and African Diasporic Art at the Georgia Museum of Art, and Dr. Steven Zucker
A conversation with Dr. Steven Zucker and Dr. Beth Harris in front of HBRA Architects, United States Federal Building and Courthouse, 2011, Tuscaloosa, Alabama. A Seeing America video
The Nernst equation relates the instantaneous potential, E, to the standard potential, E°, and the reaction quotient, Q: E = E° - (0.0592 V/n)logQ at 298 K. When all reactants and products are in their standard states, Q = 1 and E = E°. When the reaction is at equilibrium, Q = K and E = 0.
Thermodynamics tells us what can occur during a process, while kinetics tell us what actually occurs. Some processes, such as the conversion of diamond to graphite, are thermodynamically favored but kinetically unfavored. In these cases, the processes do not occur to any measurable extent.
The standard change in free energy, ΔG°, for a reaction is related to its equilibrium constant, K, by the equation ΔG° = -RTlnK. When ΔG° < 0, K > 1, and the reaction is product-favored at equilibrium. When ΔG° > 0, K < 1, and the reaction is reactant-favored at equilibrium. When ΔG° = 0, K = 1, and the reaction is at equilibrium under standard state conditions.
When ΔH° and ΔS° for a reaction have the same sign, the thermodynamic favorability of the reaction depends on temperature. In this video, we'll determine the thermodynamic favorability of a reaction with ΔH° < 0 and ΔS° < 0 at two different temperatures. We'll also calculate the temperature at which the reaction changes from being thermodynamically favored to thermodynamically unfavored.
The standard Gibbs free energy change, ΔG°, indicates the thermodynamic favorability of a physical or chemical process. When ΔG° < 0, the process is thermodynamically favored. For a given process, the value of ΔG° can be calculated directly from the values of ΔH° and ΔS° using the following equation: ΔG° = ΔH° - TΔS°.