REVISION QUESTIONS ON UNILORIN ELE 201 (APPLIED ELECTRICITY I) prepared by Engr. Abdulrahaman Okino Otuoze

Department of Electrical and Electronics Engineering Faculty of Engineering and Technology, University of Ilorin.

ELE 201 REVISION QUESTIONS QUESTION 1

1. Explain what is meant by capacitance of a capacitor.
2. Four capacitors have capacitances of 2 , 4 , 5 and 10 . Find the total capacitance when they are connected in
   1. series
   2. parallel
   3. if they are connected in parallel across a 200 supply, determine the charge on each capacitor.
   4. if they are connected in series across a 200 supply, determine the charge on each capacitor.
3. (i) A capacitor is made with 12 metal plates and each plates are separated by sheets of mica having a thickness of 0.35 and a relative permittivity of 8.

If the area of one side of each plate is 320 , determine the capacitance in. A potential difference of 400 is maintained across the terminals of the capacitor, calculate the

• 1. charge
  2. electric field strength
  3. electric flux density

QUESTION 2

1. A capacitor consists of two metal plates each of 500 × 500 spaced 6 apart. The space between the metal plates is filled with a glass plate 4 thick and the remaining space filled with a layer of paper. The relative permittivity of the glass and the paper are 8 and 2 respectively. Calculate the
   1. capacitance neglecting fringing flux and
   2. potential gradient in each dielectric in / due to a p.d of 10 between the metal plates.
2. Show that the force of attraction, between oppositely charged plates is given as

= ¹ 2 ( )

If is the supply voltage in volts, the absolute permitivity, the cross sectional area of the dielectric in and the separation of the plates in .

1. Derive the equation for the instantaneous voltage across a charging capacitor and hence the capacitor charging current.
2. Given the circuit if fig. Q2d below, determine the
   1. time constant
   2. voltage at 1 , 2 , 3 , 4 and 5 when (0) = 0V
   3. voltage at 1 , 2 , 3 , 4 and 5 when (0) = 3V
   4. sketch the results of (iii) above on a graph sheet to show the charging characteristics

QUESTION 3

of a capacitor

1. Given the circuit of Fig.Q3b below, determine the

(i)

(ii)

(iii)

(iv)

1. A 50 F capacitor is charged from a 200V supply. After being disconnected, it is immediately connected in parallel with a 20 F capacitor. Find the
   1. p.d across the combination and
   2. electrostatic energies before and after the capacitors are connected in parallel. The 20 F capacitor is initially uncharged.

1. A conductor 0.6 long is carrying a current of 75A and is placed at right angle to a magnetic field of uniform flux density. Calculate the value of the flux density if the mechanical force on the conductor is 30N.

QUESTION 3

1. Derive the equation for the current growth in an inductive circuit.
2. A coil having a resistance of 5Ω and a contstant inductance of 1.8H is switched across a 25V d.c. supply. Calculate the
   1. time constant
   2. final value of the current
   3. value of the current 1.25s after the switch is closed.
3. A 200-V dc supply is suddenly switched across a relay coil with a time constant of 5 . If the current in the coil reaches 0.35A after 4 , determine the
   1. final value of the current, the resistance and the inductance of the coil.
   2. Energy stored in the magnetic field when the current has reached its final steady value
4. A ferromagnetic ring of cross-sectional area 1000 and of mean radius 200 has two windings connected in series, one of 500 turns and one of 800 turns. If the relative permeability is 1250, calculate the self-inductance of each coil and mutual inductance of each assuming that there is no flux

leakage. (hint: = , = , = )

QUESTION 4

1. Define the following terms:
   1. Waveforms
   2. Instantaneous value
   3. Cycle
   4. Period
   5. Alternation
   6. Frequency
   7. Amplitude
   8. Peak-to Peak Value

1. Describe a brief experiment to demonstrate the rms value of an alternating current.
2. A voltage 100sin 314 volts is maintained across a circuit consisting of a halfwave rectifier in series with a 50Ω resistor. The resistance of the rectifier may be assumed to be negligible in the forward direction and infinity in reverse direction. Calculate the average and the rms value of the current.
3. An alternating voltage is represented by the equation = 140.5 sin 377 ; what are the values of its
   1. rms voltage
   2. frequency
   3. instantaneous voltage when = 4.5

QUESTION 5

1. In fig.Q5a below, given that = 12 sin 340 , determine the average power dissipated in the resistor.

1. If the voltage across a 0.01 F capacitor is 240 sin(1.25 × 10 − 30), what is the peak current, rms value of the current and the peak power absorbed.
2. Given the following pairs of instantaneous current and voltages, sketch the waveform and the phasor diagrams in each case.

1. Sketch an arbitrary impedance diagram for an R-L series circuit, R-C series circuit and R-L-C series circuit.

QUESTION 6

1. Explain the significance of power factor in any circuit.
2. Explain why the power consumed by a pure inductive or capacitive circuit is zero.
3. Differentiate between true power and reactive power.
4. Sketch an arbitrary power triangle for an R-L series circuit, R-C series circuit and an R-L-C series circuit.
5. What is resonance in an a.c. circuit? Explain the effect of resonance in an RL-C series circuit.
6. Given the circuit of fig.Q6f, determine the total impedance seen by the source.

QUESTION 7

1. Given the circuit of Fig.Q7a below, find the
   1. Power factor of the circuit
   2. Power consumed in the circuit
   3. Reactive power drawn by the circuit
   4. Apparent power
   5. Active component of the current
   6. Sketch the resulting phasor diagram

1. In fig.Q7b below,
   1. determine the reading of the voltmeter
   2. determine the reading of the ammeter
   3. draw the resulting phasor diagram of the circuit (iv) determine also the readings of the meters if = .

(v) Determine the phase angle and hence the power factor for the two cases

1. An R-L series circuit is connected to a voltage of = 600 sin 314 volts. The circuit current is = 24 sin(314 − ₄) amp. Find the value of the
   1. resistance
   2. inductance

QUESTION 8

1. In the circuit of fig. Q8a, Determine the total impedance, rms current and the power factor using
   1. Phasor diagram approach
   2. The method of phasor algebra and
   3. Admittance method

1. Given the following impedances,

= 10 + 20, = 5 + 10, = 0.02 + 5

• 1. , , and
  2. if all the impedances are connected in series
  3. if all the impedances are connected in parallel to one another
  4. if and connected in parallel to
  5. if all the impedances are connected in series
  6. if all the impedances are connected in parallel

Notes:

• This Revision Questions did not cover all the syllabus
• Make sure you revise all the questions and be up to date with class activities
• No exchange of any material whatsoever will be allowed during examinations

Wishing You all the Best

Engr. A. O. Otuoze,

Dept. of Electrical and Electronics Engineering, University of Ilorin.

2348058258679 2348032777695 [email protected] [email protected]

[email protected]

@engrmakama

DOWNLOAD PDF