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.
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