Question 1

A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. How a three phase induction motor operates when rotor frequency is greater than stator frequency?
A)rotor will be driven against rmf
B)rotor will be driven in direction of rmf
C)no emf will be induced
D)the losses will be maximum

Accepted Answer

When the rotor frequency is greater than the stator frequency, it means that the rotor is moving faster than the rotating magnetic field (rmf). In this scenario, the rotor will be driven against the direction of the rmf, as it tries to oppose the change causing its acceleration beyond the synchronous speed.

Question 2

A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. How a three phase induction motor operates when rotor frequency is less than stator frequency?
A)it operates as induction motor
B)emf is induced in rotor
C)rmf will rotate at synchronous speed
D)all of the mentioned

Accepted Answer

A three-phase induction motor operates on the principle that a rotating magnetic field (rmf) is created in the stator, which induces an electromotive force (emf) in the rotor. When the rotor frequency is less than the stator frequency, it still operates as an induction motor, emf is induced in the rotor, and the rotating magnetic field continues to rotate at synchronous speed. All these aspects are fundamental to its operation under these conditions.

Question 3

A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. Then the rotor emf E2 and the rotor current I2 are zero at_______________    
A)ns
B)2ns
C)zero
D)slip of 50%

Accepted Answer

The rotor emf E2 and the rotor current I2 are zero at synchronous speed (ns) because at this speed, the relative speed between the rotating magnetic field and the rotor is zero, resulting in no induced emf in the rotor.

Question 4

Consider a situation in which a welding operation is being performed with V = 20 volts, I = 200 A, and the cross-sectional area of the weld bead is 30 mm2. Estimate the welding speed if the workpiece and electrode are made of (a) aluminum, (b) carbon steel, and (c) titanium. Use an efficiency of 75%.
A)35 mm/s
B)34.5 mm/s
C)36 mm/s
D)46 mm/s

Accepted Answer

The welding speed can be estimated using the formula: Speed = (Efficiency * Power) / (Cross-sectional Area * Heat of Fusion). Given the same efficiency and power, the speed will be similar for different materials. The calculation results in approximately 34.5 mm/s.

Question 5

In arc welding, arc is created between the electrode and work by?
A)contact resistance
B)flow of voltage
C)flow of current
D)electrical energy

Accepted Answer

The answer of In arc welding, arc is created between...

Question 6

The coating material used for the electrode is termed as?
A)flux
B)slag
C)protective layer
D)deoxidiser

Accepted Answer

The coating material used for the electrode is termed as flux. This coating helps stabilize the arc, protect the molten weld pool from atmospheric contamination, and can also influence the mechanical properties of the weld.

Question 7

Which of the following welding process in which two pieces to be joined are overlapped and placed between two pointed electrodes?
A)seam welding
B)resistance welding
C)projection welding
D)spot welding

Accepted Answer

Spot welding involves overlapping two pieces of metal and placing them between two pointed electrodes to create a weld at specific points.

Question 8

In which of the following type of flame, oxygen is of same proportion with acetylene?
A)neutral flame
B)oxidizing flame
C)carburizing flame
D)both oxidizing flame and carburizing flame

Accepted Answer

A neutral flame occurs when oxygen and acetylene are burned in equal proportions, resulting in a balanced flame ideal for welding most metals.

Question 9

If the open circuit voltage is 60 volt and the short circuit current is 20 amperes. Then determine the voltage required for welding if the current required during welding is 10 amperes?
A)30 v
B)60 v
C)20 v
D)40 v

Accepted Answer

The voltage required for welding can be determined using the internal resistance of the power source, which is calculated from the open circuit voltage (Voc) and the short circuit current (Isc). The internal resistance (R) is Voc/Isc = 60V/20A = 3 ohms. When welding with 10 amperes, the voltage drop across the internal resistance is I*R = 10A*3ohms = 30V. Therefore, the voltage required for welding is the open circuit voltage minus this voltage drop, which is 60V - 30V = 30V.

Question 10

How does the arc voltage V depends upon the length of arc L?
A)v = f(l)
B)v = 1/f(l)
C)v = f(l2)
D)v = f(?l)

Accepted Answer

Arc voltage V depends on the length of the arc L, typically in a direct relationship, where V = f(L) indicates that the voltage is a function of the arc length.

Question 11

What is the only difference between Plasma arc welding and TIG welding?
A)flux is not used
B)construction of torch is different
C)gas is not used
D)tungsten electrode is not used

Accepted Answer

The primary difference between Plasma Arc Welding (PAW) and Tungsten Inert Gas (TIG) welding lies in the construction of the torch. In PAW, the torch design allows the plasma arc to be forced through a fine bore hole in the nozzle which focuses the arc, whereas in TIG welding, the arc is not as tightly focused.

Question 12

In plasma arc welding the gas is?
A)ionized
B)heated
C)magnetized
D)vaporized

Accepted Answer

In plasma arc welding, the gas is ionized to create a plasma, which conducts electricity and generates the heat necessary for welding.

Question 13

If the total efficiency is 0.35 in arc welding. Then what is the welding speed in mm/sec if the cross-sectional area is 5mm2, welding power is 2 kW and the heat required in melting the metal is 100 J/mm3.
A)1.4
B)14
C)1400
D)140

Accepted Answer

The welding speed (v) can be calculated using the formula: v = (η * P) / (A * H), where η is the efficiency (0.35), P is the power (2000 W or 2 kW), A is the cross-sectional area (5 mm²), and H is the heat required per unit volume (100 J/mm³). Substituting the given values: v = (0.35 * 2000) / (5 * 100) = 1.4 mm/sec.

Question 14

Which of the following inert gas is used with DC power supply only? A)argon B)helium C)CO₂ D)nitrogen

Accepted Answer

CO₂ is not a recognized chemical symbol or inert gas. The correct answer is based on the assumption that this choice is intended to represent a placeholder or error in the question. Typically, inert gases like argon and helium can be used with both AC and DC power supplies in various applications, including welding. Nitrogen, while an inert gas, is not commonly used in contexts where the distinction between AC and DC power supply usage is relevant. The question seems to be flawed or based on a misunderstanding.

Question 15

Which kind of resistance is experienced in upset butt welding?
A)electric resistance
B)magnetic resistance
C)thermal resistance
D)air resistance

Accepted Answer

Upset butt welding is a type of resistance welding where the parts to be joined are heated by the resistance to electric current flow through the materials and the force applied to join the parts.

Question 16

How are the metals to be welded connected to each other in spot welding?
A)electric contact
B)magnetic field
C)mechanical pressure
D)direct contact

Accepted Answer

In spot welding, mechanical pressure is applied to hold the metal pieces together while an electric current passes through them to create the weld.

Question 17

Up to what thickness, can steel be welded using spot welding process?
A)10 mm
B)11 mm
C)12 mm
D)13 mm

Accepted Answer

The answer of Up to what thickness, can steel be...

Question 18

In flash butt welding, the forced out metal is called flash.

Accepted Answer

In flash butt welding, the metal that is expelled during the welding process due to the heat and pressure is indeed referred to as "flash." This occurs as the parts are brought together and current is applied, causing the material at the interface to heat, melt, and be expelled, creating a strong joint once the metal cools and solidifies.

Question 19

In friction welding process, materials are joined by__________motion between materials.
A)rectilinear
B)rubbing
C)translatory
D)brownian

Accepted Answer

In friction welding, materials are joined by rubbing motion between them. This process generates heat through friction, which helps to fuse the materials together.

Question 20

All metallic engineering materials which are__________can be friction welded.
A)soft
B)weldable
C)forgeable
D)metamaterials

Accepted Answer

All metallic engineering materials that are forgeable can be friction welded. This is because friction welding involves the generation of heat through mechanical friction between the workpieces, followed by the application of a forgeable force to join the materials. If a metal can be forged, it means it can be deformed into a desired shape under compressive forces without cracking, making it suitable for the friction welding process.

Quiz 10: Three Phase Induction Motors and Welding Processes

A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. How a three phase induction motor operates when rotor frequency is greater than stator frequency?

A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. How a three phase induction motor operates when rotor frequency is less than stator frequency?

A three phase induction motor is sometimes called a generalized transformer in so far as voltage and frequency transformation has been concerned. Then the rotor emf E2 and the rotor current I2 are zero at_______________

In arc welding, arc is created between the electrode and work by?

The coating material used for the electrode is termed as?

Which of the following welding process in which two pieces to be joined are overlapped and placed between two pointed electrodes?

In which of the following type of flame, oxygen is of same proportion with acetylene?

If the open circuit voltage is 60 volt and the short circuit current is 20 amperes. Then determine the voltage required for welding if the current required during welding is 10 amperes?

How does the arc voltage V depends upon the length of arc L?

What is the only difference between Plasma arc welding and TIG welding?

In plasma arc welding the gas is?

If the total efficiency is 0.35 in arc welding. Then what is the welding speed in mm/sec if the cross-sectional area is 5mm2, welding power is 2 kW and the heat required in melting the metal is 100 J/mm3.

Which of the following inert gas is used with DC power supply only?

Which kind of resistance is experienced in upset butt welding?

How are the metals to be welded connected to each other in spot welding?

Up to what thickness, can steel be welded using spot welding process?

In flash butt welding, the forced out metal is called flash.

In friction welding process, materials are joined by__________motion between materials.

All metallic engineering materials which are__________can be friction welded.