CBSE Class 12 Physics || Current Electricity || Full Chapter || by Shiksha House
Best for NEET・2 minutes read
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.
