Lecture Sources 2.2 Ohm’s Law 2.4 Kirchhoff’s Laws
Voltage and Current Sources
Independent Sources
Characteristics An independent source establishes a voltage or current in a circuit without relying on voltages and currents elsewhere in the circuit. The value of the voltage or current supplied is specified by the value of the independent source alone.
Exercise
Dependent Sources
Characteristics Dependent sources establish a voltage or current whose value depends on the value of a voltage or current else where in the circuit. You cannot specify the value of a dependent source unless you know the value of the voltage or current on which it depends.
Exercise
What value of Vg is required for the wiring to be valid?
Ohm’s Law
Analogy The height of the water=voltage The volume of flow through the hole per second=current The smallness of the hole = resistance Water wheel hit by the flow from the hole = power
Thought Experiment #1 Fixed hole dimension↔ Fixed R Height of water↑ → flow rate↑. V↑ → I↑
Thought Experiment #2 Fixed height of water↔ Fixed V Hole dimension↑ → flow rate↑ R↓ → I↑
Derivation of Ohm’s Law Three variables: V,I and R. Different Possibilities: – V=IR (1) – I=VR (2) – R=VI (3) Intuition – If R is constant, V↑ → I↑. (3) is not possible. (1) and (2) are possible. – If V is constant, R↓ → I↑. (2) and (3) are not possible
Ohm’s Law V=IR Mnemonic: Victory Is Rare
Exercise Calculate the value v a Determine the power dissipated in the resistor
Exercise Calculate i d
Kirchhoff’s Laws
KCL Kirchhoff’s Current law (KCL) – The algebraic sum of all the currents at any node in a circuit equals zero
Exercise Sum the currents at each node
Multisim Demo
KVL Kirchhoff’s Voltage Law – The algebraic sum of all the voltage around any closed path in a circuit equals zero
Exercise Sum the voltages around each designated path in the circuit
Example KCL at b 2.KVL around cabc loop 3.Solve for i o and i 1
Problem KCL at the top node 2.KVL around the right loop 3.Find i 1, i 2, v o
Problem 2.21 Find i 1 if i 0 is 1A.