ac fundamentals trial end-semester test

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A.C. Fundamentals Trial End-Semester Test_____________________________________________________________________________________________

Lubomir Tchervenkov Page 1 of 16 www.Lubomir.name/engineering

AC ELECTRICAL FUNDAMENTALS

TRIAL END-SEMESTER TEST

This test is closedbook, calculator permitted. Time permitted 1 hours. Answer questions in the spaces provided. 60 MARKS TOTAL (70% pass) Clearly label all currents, resistors and voltage drops in the circuits and state any assumptions in

order to obtain a full mark

When calculating values, show clearly all steps, starting with the formula, then substituting withnumbers and finally show the measuring units of the obtained result. Otherwise NO MARKS

are given

It is permitted to use the formula sheets, given at the back of your lab book.

Q1) Determine the coefficient of coupling when m

L 1H, 1L 8H, 2L 2H [5 marks]

Q2)A certain transformer has 250 turns in its primary winding. In order to double the voltage, howmany turns must be on the secondary winding? [3 marks]

Q3)For each transformer on the figure draw the secondary voltage showing its relationship to the

primary voltage. Also indicate the amplitude. [5 marks]


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Q4)In the figure below determine sI . What is the value of LR ? [5 marks]


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Q5).What is the load resistance as seen by the source in the figure below? [5 marks]

Q6)For the previous question calculate what must be the turns ratio of the transformer in order to

reflect 200 into the primary circuit? [3 marks]

Q7) In a certain transformer, the input power to the primary is 100 W. If 5.5 W are lost in thewinding resistances, what is the output power to the load, neglecting any other loses? [2 marks]

Q8) What is the efficiency of the transformer in the previous problem? [2 marks]

Q9) Determine the coefficient of coupling for a transformer in which 2% of the total flux generated

in the primary does not pass through the secondary. [2 marks]

Q 10)What kVA rating is required for a transformer that must handle a maximum load current of

10A with a secondary voltage of 2.5 kV? [3 marks]


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Q 11)Determine each unknown voltage indicated in the figure [5 marks]

Q 12) Using the indicated secondary voltages in the figure, determine the turns ratios of eachtapped section of the secondary winding to the primary winding. [5 marks]


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Q13)Locate the following numbers on the complex plane. [4 marks]

Q 14)Locate the points represented by each of the following coordinates on the complex plane

[3 marks]

A.) 3 +j5

B.) -7 +j1

C.) -10 j10

Q 15)Convert 50 j200 into polar form. [1 mark]


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Q 16)Convert 25 -135 into rectangular form. [1 mark]

Q 17) Express 5310 using a negative angle to represent the positive angle [1 mark]

Q 18)Write the polar expressions for each phasor in the figure below. Convert these numbers into

rectangular form [5 marks]

Q 19)Add the following numbers: [3 marks]

(9 + j3) + (5 + j8) =

1245 + 20 32 =

Q 20)Divide the following numbers: [3 marks]

850 2.5 39 =

(40 j30) (16 + j8) =


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Q 21)Determine the impedance magnitude and phase angle in the following circuits [4 marks]


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Q 22)In the diagram below determine the current and the voltage drops. Draw the phasor diagram

for the voltages. Double check your work by adding the voltage drops. [6 marks]


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Q 24)Find the impedance in the figure below and express it in a polar form. [2 marks]

Q 25)In the previous circuit, if the frequency of the source voltage is doubled, from the value that

produces the indicated reactances, how does the magnitude of the impedance change? [1 mark]

Q 26) For the same circuit in Q. 24, determine the net reactance that will make the impedance

magnitude equal to 100 . [2 marks]

Q 27) Again for the circuit in Q. 24, is the resonant frequency higher or lower than the setting

indicated by the reactance values? [2 marks]


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Q 28)Calculate the current and the voltage drops in the following diagram, check your answers by

adding the voltages together and draw the voltages phasor diagram. [6 marks]


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Q 29)Express the impedance of the circuit below in rectangular form. [3 marks]

Q 30)Is the circuit in the previous question Q29 more capacitive or more inductive. Explain.

[1 mark]

Q 31) At what frequency does the circuit given in Q29 change its reactive characteristic from

inductive to capacitive or vice versa? [1 mark]


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Q 32)For the circuit given in Q29 find all currents. Double check your work by finding the total

current using the total impedance. Draw the current phasor diagram. [5 marks]

Q 33) Calculate all the currents and the voltage drops in the circuit below. Double check your work

by adding the currents and the voltage drops together. [15 marks]

10 mH

200

10 V, 0f = 1 kHz

1 F

100


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Q 34)Calculate all the currents and the voltage drops in the circuit below. Double check your work

by adding the currents and the voltage drops together. [15 marks]

10 mH

200

10 V, 0

1 kHz

1 F

100


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ac fundamentals trial end-semester test

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