Department of Electrical and Electronics Engineering Faculty of Engineering and Technology, University of Ilorin.
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ELE 201 REVISION QUESTIONS QUESTION 1
 Explain what is meant by capacitance of a capacitor.
 Four capacitors have capacitances of 2 , 4 , 5 and 10 . Find the total capacitance when they are connected in
 series
 parallel
 if they are connected in parallel across a 200 supply, determine the charge on each capacitor.
 if they are connected in series across a 200 supply, determine the charge on each capacitor.
 (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

 charge
 electric field strength
 electric flux density
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QUESTION 2
 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
 capacitance neglecting fringing flux and
 potential gradient in each dielectric in / due to a p.d of 10 between the metal plates.
 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 .
 Derive the equation for the instantaneous voltage across a charging capacitor and hence the capacitor charging current.
 Given the circuit if fig. Q2d below, determine the
 time constant
 voltage at 1 , 2 , 3 , 4 and 5 when (0) = 0V
 voltage at 1 , 2 , 3 , 4 and 5 when (0) = 3V
 sketch the results of (iii) above on a graph sheet to show the charging characteristics
QUESTION 3
of a capacitor
 Given the circuit of Fig.Q3b below, determine the
(i)
(ii)
(iii)
(iv)
 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
 p.d across the combination and
 electrostatic energies before and after the capacitors are connected in parallel. The 20 F capacitor is initially uncharged.
 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
 Derive the equation for the current growth in an inductive circuit.
 A coil having a resistance of 5Ω and a contstant inductance of 1.8H is switched across a 25V d.c. supply. Calculate the
 time constant
 final value of the current
 value of the current 1.25s after the switch is closed.
 A 200V 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
 final value of the current, the resistance and the inductance of the coil.
 Energy stored in the magnetic field when the current has reached its final steady value
 A ferromagnetic ring of crosssectional 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 selfinductance of each coil and mutual inductance of each assuming that there is no flux
leakage. (hint: = , = , = )
QUESTION 4
 Define the following terms:
 Waveforms
 Instantaneous value
 Cycle
 Period
 Alternation
 Frequency
 Amplitude
 Peakto Peak Value
 Describe a brief experiment to demonstrate the rms value of an alternating current.
 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.
 An alternating voltage is represented by the equation = 140.5 sin 377 ; what are the values of its
 rms voltage
 frequency
 instantaneous voltage when = 4.5
QUESTION 5
 In fig.Q5a below, given that = 12 sin 340 , determine the average power dissipated in the resistor.
 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.
 Given the following pairs of instantaneous current and voltages, sketch the waveform and the phasor diagrams in each case.
(i)  =  sin  
=

sin(  + ∅)  
(ii)  =  sin  
=

sin(  − ∅)  
(iii)  =  sin  
=

sin  −
2 

(iv)  =  sin  
=

sin  +
2 

(v)  =
= 
sin sin  +
+ 2 
 Sketch an arbitrary impedance diagram for an RL series circuit, RC series circuit and RLC series circuit.
QUESTION 6
 Explain the significance of power factor in any circuit.
 Explain why the power consumed by a pure inductive or capacitive circuit is zero.
 Differentiate between true power and reactive power.
 Sketch an arbitrary power triangle for an RL series circuit, RC series circuit and an RLC series circuit.
 What is resonance in an a.c. circuit? Explain the effect of resonance in an RLC series circuit.
 Given the circuit of fig.Q6f, determine the total impedance seen by the source.
QUESTION 7
 Given the circuit of Fig.Q7a below, find the
 Power factor of the circuit
 Power consumed in the circuit
 Reactive power drawn by the circuit
 Apparent power
 Active component of the current
 Sketch the resulting phasor diagram
 In fig.Q7b below,
 determine the reading of the voltmeter
 determine the reading of the ammeter
 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
 An RL 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
 resistance
 inductance
QUESTION 8
 In the circuit of fig. Q8a, Determine the total impedance, rms current and the power factor using
 Phasor diagram approach
 The method of phasor algebra and
 Admittance method
 Given the following impedances,
= 10 + 20, = 5 + 10, = 0.02 + 5

 , , and
 if all the impedances are connected in series
 if all the impedances are connected in parallel to one another
 if and connected in parallel to
 if all the impedances are connected in series
 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]
@engrmakama
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