Electrical Engineering Test

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Electrical Engineering Test - 1

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Question 1
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Equal area criteria and Swing equation are used for _______ and _________ stability respectively.

A
Steady state, Transient

B
Transient, Steady state

C
Both are used for steady state stability

D
Both are used for transient stability

Solution

Explanation:

Equal area criteria and Swing equation are used for transient and steady-state stability respectively.

The ability of a synchronous power system to return to stable condition and maintain its synchronism following a relatively large disturbance arising from very general situations like switching ON and OFF of circuit elements, clearing of faults, etc. is known as transient stability.

Steady-state stability is defined as the capability of an electric power system to maintain its initial condition after a small interruption or to reach a condition very close to the initial one when the disturbance is still present.
Question 2
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Consider the circuit shown below:

The average power absorbed by the 60Ω resistor (in mW) is:

A
1.754

B
1754.46

C
877.23

D
0.877

Solution
Question 3
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The output voltage of an inverter is controlled by a multiple pulse modulation technique. If the peak value of reference voltage is 4 V and the peak value of carrier voltage is 6V, then the total pulse width in each half cycle is:

A
30°

B
40°

C
50°

D
60°

Solution

Concept:

The pulse width of the waveform obtained from the PWM technique is

PW = π(1 - m_a) = 2d

m_a = Modulation index
Question 4
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An ammeter has a full-scale deflection of 50A. On performing an experiment, five values of current were recorded: 48.2, 49.6, 48.2, 49.5, and 48.2

48.2A is a ________ value and 49.6A is a ___________value

A
rated, precise

B
precise, rated

C
accurate, precise

D
precise, accurate

Solution

Explanation:

Accuracy- It is the closeness with which the instrument approaches the true value of a quantity being measured.

Hence, 49.6 is an accurate value.

Precision- It is the measure of reproducibility of the measurements.

Hence, 48.2 is a precise value.

Additional Information

Characteristics of a measuring instrument:

Sensitivity- The smallest changes in the measured variable to which the instrument responds is known as sensitivity.

Resolution- It is the smallest quantity being measured that can be detected with certainty by an instrument.

Dead Zone- for the largest range of values of a measured variable, to which the instrument does not respond.

Drift- It is an undesired change in the output of a measured variable over a period of time that is unrelated to the changes in output, operating conditions, and load.
Question 5
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A
1 and 3 Only

B
1, 3 and 5 Only

C
1, 2, 3, 4 and 5

D
All are Incorrect

Solution
Question 6
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In the circuit shown below the OP-AMP is ideal, then V_o is given by:

A
sin (t - 45°)

B
√2 sin (t)

C
√2 sin (t - 45°)

D
2 sin (t)

Solution

Calculation:
Question 7
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When bundle conductor are used in place of single conductor the effective inductance and capacitance will, respectively

A
increase and decrease

B
Decrease and increase

C
Increase and will remain unaffected

D
Decrease and will remain unaffected

Solution
Question 8
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For the given digital circuit. NOT gate is having a time delay of 5 msec. Find for which time range the LED will glow up.

X input is logic 1 for 10 msec to 35msec as shown in the figure. (logic 1 is considered as 5 V and logic 0 as 0 V)

A
10- 15msec

B
20- 25msec

C
30- 35msec

D
35- 40msec

Solution

The correct answer is 35- 40msec

Solution:

output F = (X + Y)'

waveforms are given as

As we can see for the time 35m sec to 40m sec output F is logic 1 (5 V)
Question 9
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Determine the magnitude of the EMF (in V) induced between the axis of rotation and the rim of the disc, when the disc of radius 10 cm rotates with an angular velocity of 10 revolutions per second, which is placed in a magnetic field of 4 T acting parallel to the rotation of the disc.

A
0.5

B
0.75

C
1

D
1.25

Solution
Question 10
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A 230 V, 250 RPM, 100 A Seperatly excited DC motor having r₍_a) = 0.5Ω, is connected to a 230 V supply and rated field current. The graph between load torque T_L and ω (radian/sec) is shown below, Find at what speed the motor is rotating?

A
300 RPM

B
400 RPM

C
200 RPM

D
250 RPM

Solution

The correct answer is 300 RPM

Concept:

Induced emf of the machine is