SSC JE 2015 Electrical question paper with solution and Explanation | MES Electrical

Ques 1. How much energy is stored in a 100 mH inductance when a current of 1A is flowing through it?

5.0 J

0.05

0.5 J

0.005 J✔

The energy stored in the magnetic field of an inductor can be expressed as

E = 1/2 L I^{2}

where

E = energy stored (joules, J)

L = inductance (henrys, H)

I = current (amps, A)

1/2(100 x 10^{-3} x 1)

50 x 10^{-3} J

0.05 J

Ques 2. For the circuit shown below, find the resistance between points P & Q

1 Ω✔

2 Ω

3 Ω

4 Ω

Ques 3. The rate of change of current in a 4 H inductor is 2 Amps/sec. Find the voltage across inductor

8 V ✔

16 V

2 V

0.8 V

Here L = 4H and di/dt = 2 A

Hence voltage Across inductor

= V = L(di/dt)

= 4 x 2 = 8 V

Ques 4. Find the node voltage VA

6 V ✔

5.66 V

6.66 V

5 V

Ques 5. In a pure inductive circuit if the supply frequency is reduced to half the current will?

Be four times as high

Be doubled

Be reduced to half

Be reduced to one fourth

The amplitude of the current in a pure inductive circuit is given by

Im = Vm/ωl

And ω = 2πf

Im = Vm/2πfl

Im ∝ 1/f

Hence, when the frequency is halved, the amplitude of the current is doubled in a pure inductive circuit.

Ques 6. A 10 pole 25 Hz alternator is directly coupled to and is driven by 60 Hz synchronous motor then the number of poles in a synchronous motor is?

24 poles ✔

48 poles

12 Poles

None of the above

Number of poles of alternator Pa = 10

F = 25 Hz (alternator)

F = 60 Hz (motor)

Then the number of poles of motor Pm =?

Since synchronous motor is directly coupled hence

Synchronous speed of an alternator = Synchronous speed of the motor

(120 x 25)/10 = (120 x 60)/ Pm

Pm = 24

Ques 7. When a source is delivering maximum power to the load the efficiency will be?

Below 50 %

Above 50%

50 %✔

Maximum

Maximum Power Transfer theorem

The maximum power is transferred when the load resistance RL is equal to internal resistance Rth or the equivalent resistance Rth.

RL = Rth

Under this condition, the same amount of power is dissipated in the internal resistance Rth and hence the efficiency is 50%.

Ques 8. In the Maxwell Bridge as shown in the figure below the value of resistance Rx and inductance Lx of a coil is to be calculated after balancing the bridge. The component value is shown in the figure at balance the value of Rx and Lx will respectively be

37.5 ohms, 75 mH

75 ohm, 75 mH

375 ohm, 75 mH ✔

75 ohm, 150 mH

A Maxwell bridge is a modification to a Wheatstone bridge used to measure an unknown inductance (usually of low Q value) in terms of calibrated resistance and inductance or resistance and capacitance.

The balanced condition for Maxwell bridge is given as

Z_{1}Z_{4} = Z_{2}Z_{3}

Here Z_{1} = Rx + jωLx

Z_{2} = 200Ω

Z_{3} = 750Ω

Z_{4} = R_{4} ||(1/ωC_{4})

Ques 9. The internal resistance of a voltage source is 10 ohm and has 10 volts and its terminals. Find the maximum power that can be transferred to the load

25 W

5 W

0.25 W

2.5 W ✔

For maximum power to be transferred from a source to a load resistance, the value of load resistance should be equal to the internal resistance of the source.

RL = R = 10Ω

current through the circuit = 10/(10+10) = 0.5 A

power transferred = I^{2}R = 0.25 x 10 = 2.5 W

Ques 10. As the load is increased the speed of the DC shunt motor is

Remain constant

Increase Proportionately

Reduces Slightly✔

Increase Slightly

For a dc shunt motor. ﬁeld current is practically constant and thus the torque is directly proportional to the armature current. Hence the torque-armature current characteristic is a straight line passing through the origin. However, due to the armature reaction under the loaded conditions of the machine. the flux decreases slightly with the load.
Since flux is practically constant for DC shunt motor.The speed of DC shunt motor is

N = K (V – IaRa)

Armature current increases as the load on the motor is increased. Thus, the speed of the dc shunt motor will fall slightly with the armature current. As the speed characteristic is only slightly drooping, the dc shunt motor is normally regarded as a constant speed motor.

10 As flux ɸ is assumed to be constant, we can say N ∝ Eb. But, as back emf is also almost constant, the speed should remain constant. But practically, ɸ as well as Eb decreases with increase in load. Back emf Eb decreases slightly more than ɸ, therefore, the speed decreases slightly. Generally, the speed decreases only by 5 to 15% of full load speed. Therefore, a shunt motor can be assumed as a constant speed motor.
So as per explanation…… option C be ho Sakte h”.

The shaded-pole motor is rugged, inexpensive, small in size, and requires little maintenance. Its stalled locked-rotor current is only slightly higher than its normal rated current so that it can even remain stalled for short periods without harm.
I hope you get your answer

Dissipates energy✔
Receives Energy
Both receives and supplies
Supplies Energy
sir,
active elements supplies the energy into the ckt and passive elements dissipates the energy.
plz check this concept it is right or wrong?

Very nice .This is Very Help full. Are your apps for this?

I am working on it jitendra the app will be available soon..Visit regularly for more update and Like our Facebook Page

Sir 22nd ques ka explanation plz??

Check your Gmail inbox swati

Sir, can please mail the answer to me too.

Check your mail Shreyas

Sir pls explain 22question

Check your mailbox Chetan Gusain

Sir,

If you have uee and basic electronics Notes or materials.

Please send me sir.

sir ans no 83 is worng plss correct it

Ans no 83 is right deepak …can you please explain us why the answer is wrong

10 As flux ɸ is assumed to be constant, we can say N ∝ Eb. But, as back emf is also almost constant, the speed should remain constant. But practically, ɸ as well as Eb decreases with increase in load. Back emf Eb decreases slightly more than ɸ, therefore, the speed decreases slightly. Generally, the speed decreases only by 5 to 15% of full load speed. Therefore, a shunt motor can be assumed as a constant speed motor.

So as per explanation…… option C be ho Sakte h”.

Your explanation is absolutely right I explained the speed of DC shunt motor working in normal operating condition.

My fault!! thanks

17 in the explanation….. as locked rotor current of a shaded pole motor is 5-6 times more than full load current

So option C be ho Sakte h ?

The shaded-pole motor is rugged, inexpensive, small in size, and requires little maintenance. Its stalled locked-rotor current is only slightly higher than its normal rated current so that it can even remain stalled for short periods without harm.

I hope you get your answer

Thanks you are awesome

22 explanation please

Check email Dipti

No 22 explanation please

No 66 it ll be C/L

Yes!! Corrected @Dipti

Sir you can check explanation from….. https://www.slideshare.net/mobile/bawaparam/made-by-param

Thanks for the Info @Chetan

Ques 58. An active elements in the circuit is one

Dissipates energy✔

Receives Energy

Both receives and supplies

Supplies Energy

sir,

active elements supplies the energy into the ckt and passive elements dissipates the energy.

plz check this concept it is right or wrong?

You are right sweeti saini . Actually, the explanation of the answer is right but i Ticked the wrong option… Thank You

Give me a answer for 22nd question plz..

sir pls mail me- explanation for qstn no.22

sir can you please explain 22 no question??