# UPPCL JE 2016 Electrical question paper with Solution (Evening Shift)

Ques 61.  The number of valence electrons in a Germanium is

1. 3
2. 4
3. 5
4. 6

The atomic number of germanium is 32. Therefore, the number of electrons in the first orbit, second orbit, third orbit, and fourth orbit of a germanium atom is 2, 8, 18, and 4 respectively. That means Germanium has 4 valence electrons.

Ques 62. Arcing contacts in a circuit breaker is usually made of

1. Copper tungsten alloy
2. Zinc mercury amalgam
3. Porcelain
4. Graphite

Arcing contacts are designed to prevent the main contacts from being damaged and can be made of alloys of silver, cadmium, tungsten, and zinc. The tungsten, cadmium, and zinc make the arcing contacts harder, so when the contacts open and close they will not deteriorate as quickly.

When the circuit breaker opens, the part of the main contact first and then the arcing contacts part, “drawing out” the arc across the air gap. When the circuit breaker closes, the arcing contacts meet first, creating the bridge for the arc to cross. This way, the main contacts are protected from carrying the arc, preserving them.

Ques 63.  An induction machine works in generating mode when slip is

1. Zero
2. 0 – 1
3. More than one
4. Negative

In generator operation, a prime mover (turbine or engine) drives the rotor above the synchronous speed therefore for generator
Nr >> Ns
S =
Ns  Nr/Ns

Therefore slip is negative in the induction generator.

Ques 64. Hall effect is used to determine

1. Carrier concentration in semiconductors
2. Conductivity
3. Mobility
4. All of the above

A Hall effect sensor is a transducer that produces its output voltage in response to changes in magnetic fields. Applications of the Hall effect sensor are

1. Determination of semiconductor type: The Hall coefficient is negative for a p-type semiconductor and positive for a p-type semiconductor. Therefore, the sign of the Hall coefficient can be used to determine whether a given semiconductor is n- or p-type.
2. Determination of carrier mobility: By measuring the Hall coefficient and conductivity of the semiconductor, carrier mobility can be determined.
3. Determination of carrier concentration: By measuring the Hall coefficient the carrier concentration in a semiconductor can be determined.
4. Measurement of magnetic fields: Hall voltage is proportional to the magnetic field intensity, for a given current through the sample. Therefore, one of the important applications of the Hall effect consists in measuring magnetic fields. Knowing the parameters of the Hall probe, and applied current, we can determine the intensity of the magnetic field.
5. Miscellaneous applications: Hall sensors are used for proximity switching, positioning, speed detection, and current sensing application.

Ques 65. The number of immobile contacts in Double Break Oil circuit Breaker is

1. 4
2. 3
3. 2
4. 1

In Double Break Oil Circuit Breaker two ﬁxed contacts are associated with the terminal bushing which makes contacts with the moving contacts during normal operating conditions.

The lever containing the moving contacts can be operated with the help of a crank. When the contacts are separated, two arcs are drawn. Thus there are two breaks in a series hence called the double break.

This can achieve rapid arc lengthening which eliminates the need for a specially fast-moving contact speed. But this introduces unequal voltage distribution across the breaks with uneven sharing of total interrupting duty. One break may take 70 to 80 percent of the interrupting duty.

Ques 66. Fluorescent material Zinc Silicate used in Fluorescent tubes gives _______ colour.

1. Green
2. Yellow
3. Pinkish White
4. Blackish grey

The ﬂuorescent material used inside the tube in the form of coating absorbs the ultraviolet rays and change them into light rays. Coating of different materials gives different colors of light and some of them are given below.

• Calcium tungstate ⇒ Blue
• Magnesium tungstate ⇒ Blue-White
• Zine Beryllium silicate ⇒ Yellow White
• Zinc Silicate ⇒ Green

Ques 67. Generally, mobility of electrons in semiconductors is _______ times the mobility of holes.

1. Two
2. Three✔
3. Four
4. Five

Mobility indicates how fast is the electron or hole moving from one place to another place. Larger mobility indicates higher conductivity. It may be noted that electron mobility is about three times hole mobility, the electron current is considerably more than the hole current.

For Germanium
Electron mobility ⇒ 3800 cm2/Vs
Hole mobility  ⇒ 1800 cm2/Vs

For Silicon
Electron mobility ⇒ 1300 cm2/Vs
Hole mobility  ⇒ 500 cm2/Vs

Ques 68. Corona losses in DC transmission is

1. Minimum
2. High
3. Infinite
4. Moderate

• The corona loss of a transmission system is proportional to (f + 25).
• For AC transmission it’s proportional to (50+25). (frequency of ac power transmission in India is 50Hz )
• The frequency of a DC system is zero. For DC transmission it’s proportional to (0+25). So corona losses in a DC system are less when compared to an AC system of the same conductor diameter and voltage.

Ques 69. The absorptivity of a perfect black body is

1. Zero
2. 0-1
3. 1
4. Cannot be determined

A body that absorbs all the radiation incident on it would then appear ‘perfectly black’ to us. This is because we observe a body due to the ‘reflection’ of radiation incident on it; and if a body absorbs all the radiation incident on it, then it would reflect no radiation. So, a body would be invisible to us or appear black to us. Such a body was called by Kirchhoff a black body.

A body whose absorptive power is unity (1) at all the wavelengths or that absorbs all incident electromagnetic radiation, regardless of frequency or angle of incidence is termed as the black body.

Ques 70. Given figure represents

1. Integrator✔
2. Differentiator
3. Summing amplifier
4. Precision rectifier

The operational amplifier integrator is an electronic integrated circuit. Based on the operational amplifier (op-amp), it performs the mathematical operation of integration with respect to time; that is, its output voltage is proportional to the input voltage integrated over time.

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