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DFCCIL’21 EE: Daily Practice Quiz. 08-September-2021

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               DFCCIL’21 EE: Daily Practices Quiz 08-Sep-2021

Each question carries 1 mark.
Negative marking: 1/4 mark
Total Questions: 06
Time: 08 min.

Q1. Which element is the best conductor of electricity?
(a) Silver
(b) Copper
(c) Aluminium
(d) Iron

Q2. The resistance of a semi-conductor on heating:
(a) Increases
(b) Decreases
(c) Remains constant
(d) None of the above

Q3. For the block diagram given in the following figure, the expansion C/R is:

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(a) (G1 G2 G3)/(1-G1 G2 )
(b) (G1 G2)/(1-G1 G2 G3 )
(c) (G1 G2 G3)/(1-G1 G2 G3 )
(d) (G1 G2)/(G3 (1-G1 G2 ) )

Q4. What is the use of higher flux density in the transformer design?
(a) For increasing the weight
(b) For decreasing the weight
(c) For reducing iron losses
(d) For improving insulation

Q5. Which of the following is binary equivalent of decimal (0.875)?
(a) 0.0110
(b) 0.1010
(c) 0.1110
(d) 0.1001

Q6. In a step-up chopper circuit, if V_s is the source voltage and α is duty cycle, then the output voltage is
(a) Vs /(1 + α)
(b) Vs (1 + α)
(c) Vs (1 – α)
(d) Vs/(1 – α)

SOLUTIONS
S1. Ans.(a)
Sol. From the above given options silver is the best conductor followed by copper, aluminium and iron.

S2. Ans.(b)
Sol. At higher temperatures, semi-conductor valence electrons are free, hence conduction occurs and resistivity decreases.

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S4. Ans.(b)
Sol. flux density (B) = ϕ/A
So, flux density is inversely proportional to the cross-sectional Area, so higher flux density means smaller Area i.e., Reduced weight of the transformer.

S5. Ans.(c)
Sol. 0.875 × 2 = 1 + 0.75
0.75 × 2 = 1 + 0.5
0.5 × 2 = 1 + 0
Here is the answer to 0.875 decimal to binary number: 0.111
Happened:0.87510 = 0.11102
Rule to remember:
A) Convert the integral part of decimal to binary equivalent
1. Divide the decimal number by 2 and store remainders in array.
2. Divide the quotient by 2.
3. Repeat step 2 until we get the quotient equal to zero.
4. Equivalent binary number would be reverse of all remainders of step 1.
B) Convert the fractional part of decimal to binary equivalent
1. Multiply the fractional decimal number by 2.
2. Integral part of resultant decimal number will be first digit of fraction binary
number.
3. Repeat step 1 using only fractional part of decimal number and then step 2 until
fractional parts become zero.
C) Combine both integral and fractional part of binary number.
EXAMPLE:
Let’s take an example for n =1.875
Step 1: Conversion of 1 to binary
1. 1/2: Remainder = 1: Quotient = 0
So equivalent binary of integral part of decimal is 1.
Step 2: Conversion of .875 to binary
For converting decimal fraction 0.875 to binary number, follow these steps:
Multiply 0.875 by 2 keeping notice of the resulting integer and fractional part. Continue multiplying by 2 until you get a resulting fractional part equal to zero (we calculate up to ten digits).
Then just write out the integer parts from the results of each multiplication to get equivalent binary number.

1. 0.875 * 2 = 1.75, Integral part: 1, fractional part: 0.75
2. 0.75 * 2 = 1.5, Integral part: 1, fractional part: 0.5
3. .5 * 2 = 1.0, Integral part: 1, fractional part: 0
So equivalent binary of fractional part of decimal is .111
Step 3: Combined the result of step 1 and 2.
Final answer can be written as:
1 + .11 = 1.111

S6. Ans.(d)
Sol. For step-up chopper:  VO=Vs/(1 – α).

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