Basic Electrical Circuits & Machines (EE-107)

Basic Electrical Circuits & Machines (EE-107) Course Teacher ShaheenaNoor Assistant Professor Computer Engineering Department Sir Syed University of Engineering & Technology.

VOLTAGE AND CURRENT LAWS In this chapter, we discuss the behavior of electric circuits. Two simple laws, Kirchhoff’s Current law and Kirchhoff’s voltage law form the foundation for circuit analysis procedure.

Voltage and Current Laws • Circuits • Series Circuit • Parallel Circuit

Series Circuits “Two components are connected in series if they have exactly one common terminal and if no other component has a terminal that shares that common connection.” Figure (a) Figure (b)

Series Circuits • A series path is one in which every component in the path is in series with another component. Analysis of Series Circuit: • Important property is that the current is the same in every series-connected component. • Another fact is its total resistance. • Total resistance is the sum of all the series-connected resistances. RT or Req = R1 + R2 + R3 + . . . • When a voltage source is connected in series circuit, the total current produced by that source is from Ohm’s Law.

Series Circuits • Example # 01: Let R1 = 2Ω; R2 = 1 Ω; V = 5Volts; I = ? • Example # 02: Find I and voltage across each resistor.

Kirchhoff’s Voltage Law (KVL): It states that “ The algebraic sum of the voltages around any closed path is zero.” V1 + V2 + V3 + . . . . . . . + VN = 0 OR • “ The sum of the voltage drops around any closed loop equals the sum of the voltage rises around the loop.”

Kirchhoff’s Voltage Law (KVL): • Example 3.2 Find vx and i .

Drill Problem 3.2 ( page 34) Determine i and vx for the figure given below.

Kirchhoff’s Voltage Law (KVL): • Other Examples:

Drill Problem 3.4 (page 37) • In the circuit, vs1 = 120V, vs2 = 30V, R1 = 30Ω and R2 = 15Ω. Compute the power absorbed by each element.

For Dependent Sources: Drill Problem 3.5 (page 38) • In the Circuit , find the Power absorbed by each of the five elements in the circuit.

Drill Problem 3.9 ( page 45) • Determine i in the given circuit.

Open Circuit • Break in a circuit path. • No current can flow through an open. • Since no current can flow through it, an open circuit has an infinite resistance (R = ∞) I = V/R = ? • Important: It is a common error that since the current in an open circuit is zero, the voltage across the open must also be zero.

For Example: What is the voltage ‘V’ across the switch terminal when the switch is open.

Voltage Divider Rule (VDR) I = ? V1 = ? V2 = ? V1 V2

For Example: • Use VDR to find V200Ω and V150 Ω. • Verify this using KVL

Parallel Circuits: • Two components are connected in parallel when they have 2 common terminal. • For Example:

Parallel Circuits: Analysis of Parallel Circuits: • Important property of parallel circuit is that every parallel-connected component has the same voltage across it.

For Example: • Find the current in each resistor.

Parallel Circuits: • Resistance in Parallel: • For 2 resistors (only)

Kirchhoff’s Current Law (KCL): It states that: • “ The algebraic sum of the current entering any node is zero” OR • “The sum of all currents entering a junction or any portion of a circuit equals the sum of all currents leaving the same.”

iA iB iD ic

Example • Find the current in the 150Ω resistor

Q-5 (a) (page 55) • Find ix in each of the circuits.

Q6 (page 55) • Find ix; if iY = 2A and iZ = 0A • Find iY; if iX = 2A and iZ = 2iYA 5A iX 3A iZ iY

Current Division Rule (CDR): • Consider 2 parallel resistor • Note: Parallel resistors must be branches between the same pairs of nodes.

Example: • Find I1 and I2 using the current divider rule. • Verify the result using KCL

Example 3.13 (Page 52) • Find current across 3Ω resistor using CDR.

Short Circuit • A short circuit is a path of zero resistance. • A component is said to be short-circuited when there is a short circuit connected in parallel with it.

Basic Electrical Circuits & Machines (EE-107)