CBSE Class 12 Physics || Current Electricity || Full Chapter || by Shiksha House

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Electric current is like flowing water, with charges moving from clouds to earth. Charges accumulate on moving cars and devices like torches need a steady current to operate.

Insights

Charges moving in a circuit create electric current, akin to water flowing in a river, and metals facilitate this flow by allowing electrons to move freely.
Kirchhoff's rules are fundamental in analyzing complex electric circuits, enabling the determination of currents through resistors and the application of these rules is essential for understanding circuit behavior.

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Recent questions

What is the analogy used to describe electric current?
Electric current is likened to flowing water in a river.
How is steady electric current calculated?
Steady electric current (I) is calculated as 5 units based on charge movement and time (T).
What is the relationship between resistance and conductivity in conductors?
Resistance (R) in a conductor is influenced by its composition, dimensions, and resistivity (ρ).
How is power dissipated in a conductor calculated?
Power dissipated in a conductor is represented by P = V^2 / R.
What are Kirchhoff's rules used for in analyzing electric circuits?
Kirchhoff's rules, including the point rule and loop rule, are explained for analyzing complex electric circuits.

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Summary

00:00

"Understanding Electric Current and Charge Movement"

Electric current is likened to flowing water in a river, with lightning showcasing charges moving from clouds to earth.
Charges accumulate on a moving car, leading to a mild shock when touched due to short-circuiting through the body.
In devices like electric torches, a steady current is essential for operation, making them glow.
A sign convention is established for the motion of charged particles, with left-to-right as positive and right-to-left as negative.
In a 10-second interval, positive and negative charged particles crossing over are quantified, resulting in net charge movement.
Steady electric current (I) is calculated as 5 units based on charge movement and time (T).
Metals, as conductors, allow for the unidirectional flow of free electrons, generating electric current.
Resistance (R) in a conductor is influenced by its composition, dimensions, and resistivity (ρ).
Conductivity (σ) and current density (J) are crucial in understanding the flow of electric current in conductors.
An electrolytic cell maintains a steady electric current, with EMF representing the potential difference between its electrodes.

26:31

Electricity Basics and Power Calculations

V = I * R where V is potential difference, I is current, and R is resistance
Maximum current provided by a cell is when R is 0, giving I max = e / R
To prevent cell damage, maximum current allowed is less than calculated
Potential difference V between points A and B is V = VA - VB
Charge flowing from A to B in time interval delta-t is Delta Q = I * delta t
Change in potential energy between A and B is Delta U potential = -I * Delta TV
Energy dissipated per unit time is power P = I * V
Power dissipated in a conductor is represented by P = V^2 / R
Power loss in transmission cables due to resistance is PC = e^2 / V^2 * RC
Equivalent resistance of series combination of resistors is Req = R1 + R2

52:17

Analyzing circuits with Kirchhoff's rules

The combination of cells is calculated as VA C = VA - VC = V ay - VB + VB - VC.
The equivalent EMF (eq) and internal resistance (req) of the cell combination are determined using equations 1, 2, 3, and 4.
The rules for calculating the equivalent EMF and internal resistance of a series combination of cells are established.
The rules are extended to any number of cells in a series combination, with specific formulas for EMF and internal resistance.
The circuit changes when the negative terminal of the first cell is connected to the negative terminal of the second cell, and E1 is greater than E2.
The potential differences and currents in a circuit with two cells connected in a parallel combination are analyzed.
Kirchhoff's rules, including the point rule and loop rule, are explained for analyzing complex electric circuits.
The application of Kirchhoff's rules to determine currents in branches of a complicated circuit is detailed.
The process of labeling currents and applying Kirchhoff's rules at nodal points to find unknown currents in a circuit is outlined.
The Wheatstone bridge circuit, its components, and the method of determining currents through resistors using Kirchhoff's rules are described.

01:18:03

Kirchhoff's Rules and Meter Bridge Equations

Kirchhoff's Junction rule is applied at points B and D, leading to equations 1 and 2.
Kirchhoff's loop rule is applied to loops ADBA and CBD, resulting in equations 3 and 4.
Special case: Values of R1, R2, R3, and R4 are chosen to make IG zero.
Equations 5 to 8 are derived by substituting IG as zero in equations 1 to 4.
Equation 9 is obtained by substituting I3 and I4 from equations 5 and 6 into equation 8.
Equation 10 establishes the relationship between the four resistors in the balanced condition.
The balanced condition is crucial for determining unknown resistance using the meter bridge.
The meter bridge setup involves a standard resistance wire, resistors, galvanometer, and jockey.
Equation 11 is used in the meter bridge circuit to find the unknown resistance.
The drift velocity of conduction electrons in a conductor under an electric field is determined by equation 6.

01:43:27

"Galvanometer Indicates Current Direction Based on EMF"

Deflection of galvanometer needle indicates direction of current in circuit based on EMF values.
If e1 < e2, net EMF is e2 - e1, current flows in direction of e2.
If e1 = e2, net EMF is zero, current in circuit is zero, galvanometer shows zero deflection.
Potentiometer consists of 10m wire with uniform cross-sectional area fixed to a board.
Potential drop across wire segment proportional to length, V = Phi L.
To measure potential difference across resistance, connect points P and Q to primary circuit, use galvanometer and jockey on potentiometer wire to find balancing length.

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