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CURRENT ELECTRICITY One Shot in 60 minutes👉NCERT Chapter 3 Class 12 Physics One shot

Arvind Academy・49 minutes read

The text covers various concepts related to current electricity, including Ohm's Law, resistivity, and Kirchhoff's Laws, with practical examples and applications in circuit analysis. It also discusses topics like resistors in series and parallel, efficiency of EMF sources, and the Wheatstone Bridge for determining unknown resistances in a balanced configuration.

Insights

  • Current direction follows conventional current, moving towards positive charge, despite the actual movement of electrons.
  • Drift velocity, determined by the formula v = e * E * tau / m, represents the average speed of free electrons shifting in the opposite direction of the electric field, influenced by factors like relaxation time and mobility.

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Recent questions

  • What is the relationship between current and resistance?

    Current is directly proportional to potential difference and inversely proportional to resistance.

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Summary

00:00

"Electricity Concepts: Ohm's Law, Current Direction"

  • The session will cover current electricity concepts in a 60-minute one-shot revision.
  • Arvind Academy offers a free app course with downloadable PDFs for further study.
  • Joining the Drona batch provides access to live classes and clears doubts in physics.
  • The direction of current is based on conventional current, moving in the direction of positive charge.
  • Current is a scalar quantity, not a vector, despite the movement of electrons.
  • Ohm's Law states that potential difference is proportional to current, with resistance as a constant.
  • Resistance depends on factors like length, cross-section area, and material nature.
  • Conductance is the inverse of resistance, measured in Siemens.
  • Current density is a vector quantity representing charges per unit area and time.
  • Non-Ohmic conductors do not follow Ohm's Law, unlike Ohmic conductors that do.

14:44

Electron drift velocity and resistivity relationships

  • Thermal velocity of electrons shifts due to the application of an electric field, resulting in drift velocity.
  • Drift velocity is the average velocity gained by free electrons in the opposite direction of the electric field.
  • Relaxation time is the average time between successive collisions of electrons.
  • Drift velocity is calculated using the formula v = e * E * tau / m.
  • Mobility is the drift speed of charge carriers when the electric field is normalized to one.
  • Resistivity in metals increases with temperature due to a decrease in relaxation time.
  • Resistivity in semiconductors decreases with temperature due to an increase in charge carriers.
  • The resistivity of electrolytes decreases with temperature due to a reduction in concentration.
  • The relationship between resistivity and temperature is expressed as r = r0 * (1 + alpha * (T - T0)).
  • An example problem involves calculating the temperature of a platinum resistance thermometer based on resistance values at different temperatures.

29:51

Understanding Electrical Energy and Power Calculations

  • Electrical energy is calculated using the formula W = P x D x T, with the unit being joule and the commercial unit being kilowatt hour.
  • Kilowatt hour is the unit of electrical energy, while kilowatt is the unit of power.
  • Calculating power in series combination of three bulbs involves the formula 1 / P = 1 / P1 + 1 / P2 + 1 / P3, while in parallel combination, power is calculated as P = P1 + P2 + P3.
  • Efficiency of a source of EMF is determined by output power divided by input power.
  • Electromotive force (EMF) is not a force but a form of energy, representing the work done by a unit positive charge in completing a round.
  • Terminal potential difference is the work done by a cell in moving a unit positive charge from one terminal to another.
  • Internal resistance of a cell depends on factors like the nature of electrolyte, concentration, distance between electrodes, and area of plate immersed in electrolyte.
  • Characteristic curves of cells help understand their functioning, with graphs showing relationships between EMF, internal resistance, and external load.
  • Series combination of cells involves connecting negative and positive terminals successively, while parallel combination connects all positive and negative terminals together.
  • Maximum current in series combination is achieved when external resistance is much higher than total internal resistance, while in parallel combination, maximum current is obtained when external resistance is much lower than total internal resistance.

44:24

"Maximizing Current in Electrical Circuits"

  • Maximum current is achieved when the external resistance is very small compared to the total internal resistance of the cell.
  • In a parallel combination of cells, the maximum current is determined by the total internal resistance and the external load.
  • In a mixed combination of series and parallel cells, the current in the circuit is calculated using specific formulas based on the number of cells and their internal resistances.
  • Kirchhoff's First Law, or KCL, states that the sum of incoming currents at a junction equals the sum of outgoing currents.
  • Kirchhoff's Second Law, or KVL, asserts that the algebraic sum of potential drops in a closed loop is zero, based on the conservation of energy.
  • Sign conventions in circuit analysis involve assigning positive or negative values to potential drops based on the direction of current flow and movement towards positive or negative terminals of cells.
  • The Wheatstone Bridge, based on Kirchhoff's Laws, is used to accurately and quickly determine unknown resistances by creating a balanced bridge configuration.
  • The balanced condition of a Wheatstone Bridge remains unchanged even if the positions of the cell and galvanometer are interchanged.
  • A numerical example involving a modified Wheatstone Bridge demonstrates the process of calculating current flow in a circuit by simplifying the network of resistances and applying the principles of balanced bridge configurations.
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