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

Ques 130. On applying mechanical stresses, a material gets electrically polarized. It must be a

1. Superconducting material
2. Piezoelectric material✔
3. Ceramic material
4. Ferroelectric material

When a material gets electrically polarized if it is subjected to mechanical stress and it also gets strained when subjected to an electric field, the material is called piezoelectric material.

The strain produced in the material when subjected to an electric field is proportional to the field applied i.e., stain ∝ E.

These are the materials that possess spontaneous polarization even in the absence of an external electric field.

The polarization of the material changes with temperature and the change in the polarization is given by

ΔP = λΔT

where, ΔT = Change in temperature

λ = Pyroeleetrieal coefficient.

Ques 131. Low voltage cables has operating voltage upto

1. 1 kV
2. 11 kV
3. 22 kV
4. 33 kV

Low voltage cables with a range up to 1 kV are used for energy distribution from the last transformer station to the customer.

Ques 132. Which of the following is not a type of resistance welding?

1. Carbon arc welding✔
2. Projection Welding
3. Seam welding
4. Flush Welding

Carbon Arc welding is one of the category of the ARC welding process.

Ques 133. _________ is not a current triggered device.

1. Thyristor
2. GTO
3. TRIAC
4. MOSFET✔

In an MOSFET, the gate is insulated from both the source and the drain by a very large resistance. Hence, there is no current flow into the gate. Therefore, it must be a voltage-controlled device.

In MOSFET, Gate is a control terminal that is separated from the main device by a layer of MOS(metal oxide silicon, an insulator), which forms a capacitor, one plate of the capacitor is metal contact for the gate and the other is P-channel of main conduction path of MOSFET.

When a control or gate signal is applied then it charges the capacitor formed by an insulator, in which the P-channel side of the capacitor is getting negatively charged or forming an N-channel for conduction between ‘Source’ and ‘Drain’ terminals which are of N-type(N-channel MOSFET).

This N-channel formed by charging of capacitor gets sufficient charge to cause conduction between ‘Source’ and ‘Drain’ terminals, at certain gate voltage, This minimum gate voltage is called ‘Threshold Voltage’. Because MOSFET,

Ques 134.  Electric field intensity at any point is equal to

1. Potential gradient at that point✔
2. Potential at that point
3. Potential difference at that point
4. Work done at that point

The electric intensity or field strength or field intensity may be defined in the following 3 ways.

⇒ It may be defined as the force experienced by a unit positive charge placed at that point. Its direction is the direction along which the force acts.

$E = \frac{F}{Q}newton/coulomb$

⇒ Electric field intensity is equal to the lines of force passing normally through a unit cross-section
at that point.

$E = \frac{Q}{{ \in A}}$

⇒ Electric field intensity is at any point in an electric field is equal to the negative potential gradient at that point.

$E = – \frac{{dV}}{{dr}}$

Ques 135. A power transistor has

1. High voltage and current
2. High Switching speed
3. Low switching speed
4. Zero power supply

A transistor is a semiconductor device used to amplify or switch electronic signals and electrical power. It is composed of semiconductor material usually with at least three terminals for connection to an external circuit.

The power transistor has a fairly high switching speed. The switching speed of the power transistor ranges from 100 n-sec to 1.5μ-sec.

Note – Power Mosfet has a very high switching speed as compared to the power transistor the switching speed of PMOSFET is 0.1n-sec

Ques 136. In argon arc welding, argon acts as a

1. Shield to protect work from getting oxidized✔
2. Filler material
3. Energy source
4. Flux

Argon is used as a shielding gas in electric arc welding processes. At the high temperatures that welding requires, the metals being welded become highly reactive to the elements in the atmosphere.

Contamination from these elements can lead to brittle welds, instability in the welding arc, and a variety of other issues.

To combat this, argon and other inert gases are sprayed around the welding arc to displace the atmosphere that would normally be present. This prevents contamination, leaving behind clean, strong welds.

Ques 137. Alternators are rated at

1. kW
2. kVA
3. kVA or kW
4. kWh

The power rating of an alternator is defined as the power which can be delivered by the alternator efficiently and safely under some specific condition. Increasing the load will increase the loss in the alternator.

Fixed/Core losses such as hysteresis and Eddy current losses are primarily VOLTAGE DEPENDANT.

Copper losses I²R losses which are dissipated as heat are CURRENT DEPENDANT.

As seen the copper loss of the alternator are dependent upon current and iron loss on voltage. Hence the total loss of the alternator depends on VOLT-AMPERE. These losses are independent of load power factor. That is why the rating of the alternator is in kVA

Ques 138. Which of the following device is mainly used in DC drives?

1. Transistor
2. Diode
3. Thyristor✔
4. TRIAC

A thyristor drive is a motor drive circuit where AC supply current is regulated by a thyristor phase control to provide the variable voltage to a DC motor.

With the introduction of Thyristor or Silicon Controlled Rectifier (SCR) as a power switching device in the sixties, and later the arrival of Gate Turn-Off (GTO) thyristor, bridge rectifiers (converters) and choppers fed from ac and dc supply respectively are used for speed control of dc motors.

Choppers using GTOs are now preferred for high-power dc drives as these devices can be turned off by proper signals applied to the gate. This is unlike thyristors, which can only be turned on by gate signal i.e. cannot be turned off by the gate signal.

Ques 139. Which of the following pair is not correctly matched?

1. Mass – kg
2. Current -A
3. Temperature – °C✔
4. Luminous Intensity – Cd

The symbol of temperature is K.

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Ques 140. A good Fuse wire must have

1. High Melting point
2. High Ohmic losses
3. High Conductivity✔
4. High Deterioration

A fuse is a safety device consisting of a strip of wire that melts and breaks an Electric circuit if the current exceeds the safe value.

Characteristics of a fuse are:-

1. It should have a low melting point.
2. It should have low ohmic losses.
3. It should have high conductivity. ( or low resistivity)
4. It should be economical.
5. It should be free from detraction.
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