lecture 2 2.1 sources 2.2 ohm’s law 2.4 kirchhoff’s laws
Post on 19-Dec-2015
226 views
TRANSCRIPT
Lecture 2
2.1 Sources2.2 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
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 RHeight of water↑ → flow rate↑.V↑ → I↑
Thought Experiment #2
Fixed height of water↔ Fixed VHole 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 va• Determine the power dissipated in the resistor
Exercise
Calculate id
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 2.8
1.KCL at b2.KVL around cabc loop3.Solve for io and i1
Problem 2.18
1.KCL at the top node2.KVL around the right loop3.Find i1, i2, vo
Problem 2.21
Find i1 if i0 is 1A.