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Ece 112: Circuit Theory Question Paper

Ece 112: Circuit Theory

Course:Bachelor Of Engineering In Electrical And Electronics Engineering

Institution: Moi University question papers

Exam Year:2009

ECE 112: CIRCUIT THEORY
1. In a certain circuit supplied from 50 Hz mains, the potential difference has a maximum value of 500 V and the current has a maximum value of 10 A. At the instant t=0, the instantaneous values of the p.d and the current are 400 V and 4 A respectively, both increasing positively. Assuming sinusoidal variation, state trigonometrical expressions for the instantaneous values of the p.d and the current at time t. Calculate the instantaneous values at the instant t=0.015 s and find the angle of phase difference between the p.d and the current. Sketch the phasor diagram.

2. An alternating i is represented by i = 10sin942t amperes. Determine:
a. The frequency
b. The period
c. The time taken from t = 0 for the current to reach a value of 6 A for a first and second time
d. The energy dissipated when the current flows through a 20 ohm resistor for 30 mins.

3. Two impedances are connected in parallel to the supply, the first takes a current of 40 A at a lagging phase angle of 30 degrees, and the second current of 30 A at a leading phase angle of 45 degrees. Draw a phasor diagram to scale to represent the supply voltage and these currents. From this diagram, by construction, determine the total current taken from the supply and its phase angle.

Ece 112: Circuit Theory Question Paper

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