Faculty of Engineering



Faculty of Engineering

ELECTRICAL AND ELECTRONIC ENGINEERING DEPARTMENT

EENG223 Circuit Theory I

INFE221 – Electrical Circuits

Midterm Exam

Spring 2009-10

20 April 2010

Duration: 90 minutes

Instructor: O. Kukrer

Solve all 5 Problems

|STUDENT’S | |

|NUMBER | |

|NAME | |

|SURNAME | |

|GROUP NO. | |

| Problem | |Points |

|1 | |20 |

|2 | |20 |

|3 | |20 |

|4 | |20 |

|5 | |20 |

|TOTAL | |100 |

1. In the circuit of Figure 1, find the current io using nodal analysis.

KCL eqn. for node 1: [pic]

[pic]

KCL eqn. for node 2: [pic]

Solving (1) and (2) [pic]

2. In the circuit of Figure 2,

(a) Find the voltage Vx using mesh analysis. (15 pts)

(b) Find the power supplied by the 4-A current source. (10 pts)

(a)

KVL eqn. for the supermesh: [pic]

[pic] (1)

KCL at node C : [pic]

[pic]

(b) Voltage across the 4-A current source [pic]

3. Use superposition to find the current i0 in the circuit in Figure 3.

1. Apply the 2A-source, turn off the 24V-source:

Nodal analysis:

KCL eqn. for node 1: [pic]

KCL eqn. for node 2: [pic]

[pic]

[pic]

2. Apply the 24V -source, turn off the 2A -source:

KCL eqn. for node 2: [pic]

[pic]

[pic]

4. Use source transformation to find the voltage v0 in the circuit in Figure 4.

Transform the dependent voltage source (6v0) in series with the 6Ω resistance to a current source:

Transform the dependent current source (v0) in parallel with the 2Ω resistance (equivalent of [pic]) to a voltage source:

KVL for the loop : [pic]

5. Obtain the Thevenin equivalent of the circuit in Figure 5 with respect to the terminals a-b.

Since the current [pic]is zero (terminals a-b are open)

[pic]

To find RTh, turn off the 10A-source, then apply a test source between a-b:

[pic]

Thevenin equivalent circuit:

-----------------------

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

[pic]

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