Basic Electrical Circuits & Machines (EE-107) Course Teacher Shaheena Noor 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
“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. R T or R eq = R 1 + R 2 + R 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. Series Circuits
It states that “ The algebraic sum of the voltages around any closed path is zero.” V 1 + V 2 + V V N = 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 v x and i. Kirchhoff’s Voltage Law (KVL):
Determine i and v x for the figure given below. Drill Problem 3.2 ( page 34)
Other Examples: Kirchhoff’s Voltage Law (KVL):
In the circuit, v s1 = 120V, v s2 = 30V, R 1 = 30Ω and R 2 = 15Ω. Compute the power absorbed by each element. Drill Problem 3.4 (page 37)
Drill Problem 3.5 (page 38) In the Circuit, find the Power absorbed by each of the five elements in the circuit. For Dependent Sources:
Determine i in the given circuit. Drill Problem 3.9 ( page 45)
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. Open Circuit
For Example: What is the voltage ‘V’ across the switch terminal when the switch is open.
Voltage Divider Rule (VDR) V1V1 V2V2 I = ? V 1 = ? V 2 = ?
Use VDR to find V 200Ω and V 150 Ω. Verify this using KVL For Example:
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. Parallel Circuits:
Find the current in each resistor. For Example:
Resistance in Parallel: For 2 resistors (only) Parallel Circuits:
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.” Kirchhoff’s Current Law (KCL):
i A i B iDiD icic
Find the current in the 150Ω resistor Example
Find i x in each of the circuits. Q-5 (a) (page 55)
Find i x ; if i Y = 2A and i Z = 0A Find i Y ; if i X = 2A and i Z = 2i Y A Q6 (page 55) 5A 3A iZiZ iYiY iXiX
Consider 2 parallel resistor Note: Parallel resistors must be branches between the same pairs of nodes. Current Division Rule (CDR):
Find I 1 and I 2 using the current divider rule. Verify the result using KCL Example:
Find current across 3Ω resistor using CDR. Example 3.13 (Page 52)
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. Short Circuit