Ques 1. Two 10 ohm resistance is connected in parallel, their effective resistance will be

5

10

7

None of the above

Answer.1. 5 ohm

Explanation:

Since the resistance are connected in parallel, therefore, their effective resistance will be

R_{1} x R_{2} / R_{1} + R_{2}

100/20 = 5 ohm

Ques 2. In a 3-phase half wave rectifier, if the input phase voltage is 200 V, the PIV required for each diode will be

400 V

346 V

370 V

200 V

Answer.2. 346 V

Explanation:

Peak inverse voltage or PIV of diode = Maximum value of secondary voltage

= 200 x √3 = 346 V

Ques 3. For 100 turns as primary, 1000 V, 100 turns secondary transformer will have an output power of?

1000 V

500 V

250 V

100 V

Answer.4. 100 V

Explanation:

Transformer ratio is given as

= 1000/100 = 1000/Vs

= Vs = 100 Volt

Ques 4. Two couple coil of L_{1} = 0.8 H and L2 = 0.2 H have a coupling coefficient of K = 0.9. The mutual inductance M is

0.144 H

0.23 H

0.36 H

0.43 H

Answer.3. 0.36

Explanation:

Mutual inductance of two coupling coil is

M = K√L1L2

= 0.9√0.16

= 0.36 H

Ques 5. Transformer efficiency compared to other motor is

Higher

Remain same

Lower

None of these

Answer.1. Higher

Explanation:

.As Transformer is a static device, it does not have any rotating parts hence the mechanical losses are absent which increases the efficiency of the transformer.

Ques 6. Hall effect transducer with hall coefficient K_{H} = -1 x 10-8 is required to measure a magnetic field of 10,000 gauss. A 2 mm bismuth slab is used as the transducer with a current of 3A. The output voltage of the transducer will be

-15 x 10 ^{-6} V

-7.5 x 10 ^{-6} V

10 x 10 ^{-6} V

-22.5 x 10 ^{-6} V

Answer.1. -15 x 10 ^{-6} V

Explanation:

Hall effect Output Voltage

= E_{H }= K_{H} IB / T

Where I is current

T is Thickness

B = Magnetic field = 10000 gauss = 10000 x 10^{-5} Wb/m^{2}

Ques 7. Which power plant has the minimum running cost?

Coal-based

Hydel

Nuclear

None of these

Answer.2. Hydel

Explanation:

Operating cost of the hydro plant is low because of prime fuel, pressurised water comes almost free.

Ques 8. For power measurement of the three-phase circuit by two wattmeter method, when the value of power factor is less than 0.5 lagging.

One of the wattmeters will read zero

Both give the same reading

One of the wattmeter connections will have to be reversed

Pressure coil of the wattmeter will become ineffective.

Answer.3. One of the wattmeter connections will have to be reversed

Explanation:

Some point must be noted for two wattmeter method! READ THE POINT CAREFULLY

If phase angle Φ = 0°, the readings of the two wattmeters are equal.

If phase angle Φ < 60°, the readings of both the wattmeters are positive and the total power is the sum.

If phase angle Φ = 60°, the reading P2 of the wattmeter W3 is zero.

If phase angle Φ> 60°, i.e., if the power factor of the load is less than 0.5, the reading of wattmeter W2 is negative. In such case, the connection of either the current coil or the potential coil has to be reversed so that the pointer may deﬂect in the positive direction. The reading obtains after reversal of coil should then be taken as negative while calculating the power factor or the total power.

Now in the above question, the value of power factor is less than 0., therefore, one of the wattmeter connections will have to be reversed.

Ques 9. Which efficiency is more in case of cell

Watt-hour efficiency

Ampere-hour Efficiency

Output Power efficiency

None of the these

Answer.2. Ampere-hour Efficiency

Explanation:

The amp-hour is a unit of battery energy capacity hence Ampere hour efficiency is more in case of the cell and ampere-hour efficiency is always greater than watt-hour efficiency

Ques 10. A 1000 ohms/V meter is used to measure a resistance on 150 V scale. The meter resistance is

150 KΩ

1K

6.67 ohms

0.001 Ohms

Answer.1. 150 KΩ

Explanation:

Resistance of Voltmeter = sensitivity in ohm × voltage in volts

Ques 93. The insulation resistance of a cable of length 10 Km is 1 MΩ. Its resistance for 50 Km length will be
1 MΩ
0.5 MΩ
0.2 MΩ
None of these
Hide Explanation
Answer.2. 0.5 MΩ
Explanation:
Insulation resistance of the cable
R α 1/Length
R2/R1 = L1/L2
Hence, insulation resistance for 50 km length
R2 = (1 x 10)/50
= 0.5 MΩ but ans is 0.2MEGA OHAM

35 The hysteresis coefficient is defined as the ratio of loss of energy per cycle to the field intensity or the intensity of electromagnetic stress in the material. Hence, the low hysteresis coefficient leads to reduce the hysteresis loss in that magnetic material.

for DC voltages, insulator capacitances are ineffective and voltage across each unit would be the same. This is why string efficiency for DC system is 100%.

Ques 93. The insulation resistance of a cable of length 10 Km is 1 MΩ. Its resistance for 50 Km length will be

1 MΩ

0.5 MΩ

0.2 MΩ

None of these

Hide Explanation

Answer.2. 0.5 MΩ

Explanation:

Insulation resistance of the cable

R α 1/Length

R2/R1 = L1/L2

Hence, insulation resistance for 50 km length

R2 = (1 x 10)/50

= 0.5 MΩ but ans is 0.2MEGA OHAM

you are Right Nplesh ” Calculation Error”

35 The hysteresis coefficient is defined as the ratio of loss of energy per cycle to the field intensity or the intensity of electromagnetic stress in the material. Hence, the low hysteresis coefficient leads to reduce the hysteresis loss in that magnetic material.

Answer might be B

Both are right @chetan Gusain in order to reduce hysteresis loss the material should have low hysteresis coefficient and low B-H curve

75 ….. answer C typing error

75 answer A

Can you please elaborate your answer

Sir you didn’t substitute the correct value as the options…. beside your explanation is ok but option is wrong.

Question no 87’s answer is 80 % or 100%

for DC voltages, insulator capacitances are ineffective and voltage across each unit would be the same. This is why string efficiency for DC system is 100%.

In Q50 how the answer is all while sp. resistance depend uponmaterial and temp.

Thanks for pointing out the Problem Balvinder the question was not right. Yesterday I uploaded the article on the same topic https://www.electrical-exam.com/concept-of-resistance-and-ohms-law/ you can check it out and Best of luck!!!