Series and Parallel Circuits

The video introduces the fundamental differences between series and parallel circuits. In a series circuit, current flows through a single path, while in a parallel circuit, current has multiple paths. Resistors are compared to light bulbs, illustrating that in series circuits, adding more resistors increases total resistance and dims bulbs, whereas in parallel circuits, adding resistors decreases total resistance but keeps individual bulbs bright as long as enough current is supplied.

The first example involves a series circuit with a 30V battery and two resistors (4 Ohms and 6 Ohms). The total resistance is calculated by simply adding the individual resistances (10 Ohms). Using Ohm's Law (V=IR), the total current is found to be 3A. The voltage drop across each resistor is then calculated (18V for 6 Ohms, 12V for 4 Ohms), demonstrating that the sum of voltage drops equals the battery voltage, in line with Kirchhoff's Voltage Law.

The video then explains how to calculate power (P=VI) using three forms: P=VI, P=I^2R, and P=V^2/R. For the previous series circuit, the power delivered by the battery is 90W. The power absorbed by each resistor is calculated (54W for 6 Ohms, 36W for 4 Ohms), showing that the total power absorbed by the resistors equals the power delivered by the battery, upholding energy conservation. Power is defined as the rate of energy transfer.

A second series circuit example with a 60V battery and three resistors (5 Ohms, 3 Ohms, 2 Ohms) is presented. The total resistance is 10 Ohms, and the current is 6A. Voltage drops across each resistor are 30V, 18V, and 12V, respectively, summing to 60V. Power calculations show the battery delivering 360W, with resistors absorbing 180W, 108W, and 72W, totaling 360W.

The video moves to parallel circuits, explaining that voltage across parallel components is the same. An example with a 24V battery and two resistors (6 Ohms and 8 Ohms) is shown. Individual currents are calculated (4A for 6 Ohms, 3A for 8 Ohms). The total current leaving the battery is the sum of these individual currents (7A), illustrating Kirchhoff's Current Law. The concept of equivalent resistance in a parallel circuit is introduced through Ohm's law and a specific formula (1/Req = 1/R1 + 1/R2...). The equivalent resistance is found to be lower than any individual resistor (3.43 Ohms).

For the parallel circuit, the power delivered by the battery is calculated as 168W. The power absorbed by each resistor is 96W for the 6 Ohm resistor and 72W for the 8 Ohm resistor, summing to 168W, thereby demonstrating power conservation.

A final parallel circuit example features a 20V battery and three resistors (2 Ohms, 4 Ohms, 5 Ohms). Individual currents are 10A, 5A, and 4A, respectively, leading to a total current of 19A from the battery. The distribution of current at junctions is explained using Kirchhoff's Current Law. Power delivered by the battery is 380W, and individual power absorption by resistors are 200W, 100W, and 80W, summing to 380W. The equivalent resistance is calculated as 1.05 Ohms, which is less than the smallest individual resistance, a characteristic of parallel circuits.

A concise review re-emphasizes that series circuits have one current path, while parallel circuits have multiple. In series, current is uniform across resistors. In parallel, voltage is uniform across resistors.