2670 + Mcqs in NTPC (Technical Ability) Page 42 McqOptions

2051.	Which of the following heating elements can give highest temperature in resistance heating?
A.	Copper
B.	Nickel copper
C.	Nichrome
D.	Silicon carbide
Answer» E.

Discussion

2052.	The device necessarily used for automatic temperature control in a furnace is
A.	thermostat
B.	auto-transformer
C.	thermo-couple
D.	any of the above
Answer» B. auto-transformer

Discussion

2053.	Wound rotor and squirrel-cage motors with high slip which develop maximum torque at stand still are used for
A.	presses and punches
B.	machine tools
C.	elevators
D.	all of these
Answer» B. machine tools

Discussion

2054.	Miniature lamps on automobiles are used for
A.	tail
B.	dash board lamp
C.	side lamp
D.	all of these
Answer» E.

Discussion

2055.	Ward-Leonard controlled d.c. drives are generally used for
A.	light duty excavators
B.	medium duty excavators
C.	heavy duty excavators
D.	all of these
Answer» D. all of these

Discussion

2056.	A gas turbine plant working on Joule cycle produces 4000 kW of power. If its work ratio is 40%, what is the power consumed by the compressor?
A.	2400 kW
B.	4000 kW
C.	6000 kW
D.	8000 kW
Answer» B. 4000 kW

Discussion

2057.	What is the ratio of the static enthalpy rise in the rotor to the static enthalpy rise in the stage of an axial flow compressor defined as?
A.	Power input factor
B.	Flow coefficient
C.	Temperature coefficient
D.	Degree of reaction
Answer» E.

Discussion

2058.	Stalling of blades in axial-flow compressor is the phenomenon of:
A.	Air stream blocking the passage
B.	Motion of air at sonic velocity
C.	Unsteady, periodic and reversed flow
D.	Air stream not able to follow the blade contour
Answer» B. Motion of air at sonic velocity

Discussion

2059.	Compared to axial compressors centrifugal compressors are more suitable for:
A.	High head, low How rate
B.	Low head, low flow rate
C.	Low head, high how rate
D.	High head, high flow rate
Answer» D. High head, high flow rate

Discussion

2060.	The pressure rise in the impeller of centrifugal compressor is achieved by:
A.	The decrease in volume and diffusion action the
B.	Centrifugal action and decrease in volume
C.	The centrifugal and diffusion action
D.	The centrifugal and push-pull action.
Answer» E.

Discussion

2061.	The thermal efficiency of a gas turbine cycle with regeneration in terms of \[{{T}_{3}}\] (maximum temperature),\[{{T}_{1}}\] (minimum temperature) \[{{r}_{p}}\] (pressure ratio) and \[k-\left( \frac{{{c}_{p}}}{{{c}_{v}}} \right)\] is given by:
A.	\[1-\frac{{{T}_{1}}}{{{T}_{3}}}{{r}_{p}}^{\left( \frac{k}{k-1} \right)}\]
B.	\[1-\frac{{{T}_{1}}}{{{T}_{3}}}{{r}_{p}}^{\left( \frac{k}{k-1} \right)}\]
C.	\[1-\frac{{{T}_{3}}}{{{T}_{1}}}{{r}_{p}}^{\left( \frac{k-1}{k} \right)}\]
D.	\[1-\frac{{{T}_{1}}}{{{T}_{3}}}{{r}_{p}}^{\left( \frac{k-1}{k} \right)}\]
Answer» E.

Discussion

2062.	Consider the following statements: The reheat cycle helps to reduce 1. Fuel consumption 2. Steam flow 3. The condenser size Which of these statements are correct?
A.	1 and 2
B.	1 and 3
C.	2 and 3
D.	1, 2 and 3
Answer» B. 1 and 3

Discussion

2063.	Consider the following statements: 1. Reciprocating compressors are best suited for high pressure and low volume 2. The effect of clearance volume on power consumption is negligible for the same volume of discharge. 3. While the compressor is idling, the delivery valve is kept open by the control 4. Intercooling of air between the stages of compression helps to minimize losses. Of these statements:
A.	1 and 2 are correct
B.	1 and 3 are correct
C.	2 and 4 are correct
D.	3 alone is correct
Answer» C. 2 and 4 are correct

Discussion

2064.	The efficiency of a simple gas turbine can be improved by using a regenerator, because the:
A.	Work of compression is reduced
B.	Heat required to be supplied is reduced
C.	Work output of the turbine is increased
D.	Heat rejected is increased
Answer» C. Work output of the turbine is increased

Discussion

2065.	In an axial flow compressor design, velocity diagrams are constructed from the experimental data of aerofoil cascades. Which one of the, following statements in this regard is correct?
A.	Incidence angle of the approaching air is measured from the trailing edge of the blade
B.	\[\delta \] Is the deviation angle between the, angle of incidence and tangent to the amber line
C.	The deflection of the gas steam while passing through the cascade is given by \[\varepsilon ={{\alpha }_{1}}-{{\alpha }_{2}}\]
D.	\[\varepsilon \] Is the sum of the angle of incidence and camber less any deviation angle, i.e. \[\varepsilon =i+\theta -\delta \]
Answer» B. \[\delta \] Is the deviation angle between the, angle of incidence and tangent to the amber line

Discussion

2066.	In Centrifugal compressor terminology, vaneless space refers to the space between:
A.	The inlet and blade inlet edge
B.	Blades in the impeller
C.	Diffuser exit and volute casing
D.	Impeller tip and diffuser inlet edge
Answer» E.

Discussion

2067.	A three-stage Rateau turbine is designed in such a manner that the first two stages develop equal power with identical velocity diagram while the third one develops more with higher blade speed. In such a multistage turbine the blade ring diameter:
A.	Is the same for all the three stages
B.	Gradually increases from the first to the third
C.	Of the third stage is greater than that of the first two stages,
D.	Of the third stage is less than that of the first two stages.
Answer» C. Of the third stage is greater than that of the first two stages,

Discussion

2068.	Consider the following factors: 1. Cylinder size 2. Clearance ratio 3. Delivery pressure 4. Compressor shaft power. The factors which affect the volumetric efficiency of a single-stage reciprocating air compressor would include:
A.	1 and 2
B.	3 and 4
C.	2 and 3
D.	1 and 4
Answer» B. 3 and 4

Discussion

2069.	Which one of the following statements is the?
A.	In a multi-stage compressor, adiabatic efficiency less than stage efficiency
B.	In a multi-stage turbine; adiabatic efficiency is less than the stage efficiency
C.	Preheat factor for a multistage compressor is greater than one
D.	Preheat factor does not effect the multistage compressor performance
Answer» D. Preheat factor does not effect the multistage compressor performance

Discussion

2070.	In a De Laval nozzle expanding superheated steam from 10 bar to 0.1 bar, the pressure as the minimum cross-section will be:
A.	3.3 bar
B.	5.46 bar
C.	8.2 bar
D.	9.9 bar
Answer» C. 8.2 bar

Discussion

2071.	What will be the shape of the velocity triangle at the exit of a radial bladed centrifugal impeller, taking into account slip?
A.	Right-angled
B.	Isosceles
C.	All angles less than \[90{}^\circ \]
D.	One angle greater than \[90{}^\circ \]
Answer» D. One angle greater than \[90{}^\circ \]

Discussion

2072.	A four-stage compressor with perfect intercooling between stages compresses air from 1 bar to 16 bar. The optimum pressure in the last intercooler will be:
A.	6 bar
B.	8 bar
C.	10 bar
D.	12 bar
Answer» C. 10 bar

Discussion

2073.	In a two-stage compressor with ideal intercooling, for the work requirement to be minimum, the intermediate pressure \[{{p}_{i}}\] in terms of condenser and evaporator pressure \[{{p}_{c}}\] and \[{{p}_{e}}\] respectively is:
A.	\[pi={{p}_{c}}{{p}_{e}}\]
B.	\[pi={{p}_{i}}=\sqrt{{{P}_{a}}{{P}_{e}}}\]
C.	\[pi={{P}_{i}}=\sqrt{{{\text{P}}_{\text{a}}}\text{/}{{\text{P}}_{\text{e}}}}\]
D.	\[pi={{\text{p}}_{\text{c}}}\text{/}{{\text{p}}_{\text{e}}}\]
Answer» C. \[pi={{P}_{i}}=\sqrt{{{\text{P}}_{\text{a}}}\text{/}{{\text{P}}_{\text{e}}}}\]

Discussion

2074.	Gas turbine develops 120 kJ of work while the compressor absorbed 60 kJ of work and the heat supplied is 200 kJ. If regenerator which would recover 40% of the heat in the exhaust were used, then the increase in the overall thermal efficiency would be:
A.	0.102
B.	0.086
C.	0.069
D.	0.057
Answer» E.

Discussion

2075.	Given: \[{{v}_{w\,2}}=\] velocity of whirl at outlet \[{{u}_{2}}=\]Peripheral velocity of the blade tips The degree of reaction in a centrifugal compressor equal to:
A.	\[1-\frac{{{v}_{w\,2}}}{2{{u}_{2}}}\]
B.	\[1-\frac{{{u}_{2}}}{2{{v}_{w\,2}}}\]
C.	\[1-\frac{2{{v}_{w\,2}}}{{{u}_{2}}}\]
D.	\[1-\frac{{{v}_{w\,2}}}{{{u}_{2}}}\]
Answer» C. \[1-\frac{2{{v}_{w\,2}}}{{{u}_{2}}}\]

Discussion

2076.	Centrifugal compressors are suitable for large discharge and wider mass flow range, but at a relatively low discharge pressure of the order of 10 bars, because of:
A.	Low pressure ratio
B.	Limitation of size of receiver
C.	Large speeds
D.	High compression index
Answer» B. Limitation of size of receiver

Discussion

2077.	Once through boiler is named as such because:
A.	Flue gas passes only in one direction
B.	There is no recirculation of water
C.	Air as sent through the same direction
D.	Steam is sent out only in one direction
Answer» C. Air as sent through the same direction

Discussion

2078.	For a multistage compressor, the polytropic efficiency is:
A.	The efficiency of all stages combined together
B.	The efficiency of one stage
C.	Constant throughout for all the stages.
D.	A direct consequence of the pressure ratio.
Answer» D. A direct consequence of the pressure ratio.

Discussion

2079.	A double acting steam engine with a cylinder diameter of 19 cm and a stroke of 30 cm has a cut-off of 0.35. The expansion ratio for this engine is nearly:
A.	1.05
B.	2.85
C.	6.65
D.	10.05
Answer» C. 6.65

Discussion

2080.	In a centrifugal compressor, the highest Mach number leading to shockwave in the fluid flow occurs at:
A.	Diffuser inlet radius
B.	Diffuser outlet radius
C.	Impeller inlet radius
D.	Impeller outlet radius
Answer» C. Impeller inlet radius

Discussion

2081.	Shielding in a nuclear reactor is generally done to protect against:
A.	Excess electrons
B.	X-rays
C.	A-and P-rays
D.	Neutron and gamma rays
Answer» D. Neutron and gamma rays

Discussion

2082.	Consider the following statements: When air is to be compressed to reasonably high pressure, it is usually carried out by multistage compressor with an intercooler between the stages because 1. Work supplied is saved 2. Weight of compressor is reduced. 3. More uniform torque is obtained leading to the reduction in the size of flywheel. 4. Volumetric efficiency Of the four statements listed above:
A.	1 alone is correct
B.	2 and 4 are correct
C.	1, 2 and 3 are correct
D.	1, 2, 3 and 4 are correct
Answer» B. 2 and 4 are correct

Discussion

2083.	In a reciprocating air compressor the compression work per kg of air
A.	Increases as clearance volume increases
B.	Decreases as clearance volume increases
C.	is independent of clearance volume
D.	Increases with clearance volume only of multi-stage compressor
Answer» B. Decreases as clearance volume increases

Discussion

2084.	If (to geometrically similar impellers of a centrifugal compressor are operated at the. same speed, then their head discharge and power will vary with their diameter ratio:
A.	\[d,{{d}^{2}}\,\,and\,\,{{d}^{3}}\]Respectively
B.	\[d,\,{{d}^{3}}\,\,and\,\,{{d}^{5}}\] Respectively
C.	\[d,\,{{d}^{3}}\,\,and\,\,{{d}^{5}}\] Respectively
D.	\[{{d}^{2}},d\,\,and\,\,{{d}^{3}}\] Respectively
Answer» E.

Discussion

2085.	For a two-stage reciprocating compressor, compression from pressure \[{{p}_{1}}\] to \[{{p}_{3}}\] is with perfect intercooling and no pressure losses. If compression in both cylinders follows the same polytropic process and the atmospheric pressure is \[{{p}_{a'}}\] then the intermediate pressure \[{{p}_{2}}\] is given by:
A.	\[{{p}_{2}}=({{p}_{1}}+{{p}_{3}})/2\]
B.	\[{{p}_{2}}=\sqrt{{{p}_{1}}.{{p}_{3}}}\]
C.	\[{{p}_{2}}={{p}_{a}}\frac{{{p}_{3}}}{{{p}_{1}}}\]
D.	\[{{p}_{2}}={{p}_{a}}.\sqrt{{{{p}_{3}}}/{{{p}_{1}}}\;}\]
Answer» C. \[{{p}_{2}}={{p}_{a}}\frac{{{p}_{3}}}{{{p}_{1}}}\]

Discussion

2086.	Intercooling in gas turbines:
A.	Decreases net output but increases thermal efficiency
B.	Increases net output but decreases thermal efficiency
C.	Decreases both net output and thermal efficiency
D.	Increases both net output and thermal efficiency
Answer» C. Decreases both net output and thermal efficiency

Discussion

2087.	In a simple gas turbine power plant operating on standard Brayton cycle power needed to drive the compressor is 175 kW, rate of heat supplied during constant pressure heat addition process is 675 kW. Turbine output obtained during expansion is 425 kW. What is the rate of heat rejection during constant pressure heat rejection?
A.	75 kW
B.	425 kW
C.	500 kW
D.	925 kW
Answer» C. 500 kW

Discussion

2088.	Performance of a reciprocating Compressor is expressed by:
A.	\[\frac{Isothermal\,\,work}{Indicated\,\,work}\]
B.	\[\frac{Indicated\,\,work}{Isothermal\,\,work}\]
C.	\[\frac{Adiabatic\,\,work}{Indicated\,\,work}\]
D.	\[\frac{Indicated\,\,work}{Adiabatic\,\,work}\]
Answer» B. \[\frac{Indicated\,\,work}{Isothermal\,\,work}\]

Discussion

2089.	The state of air supplied by a cooling coil with a by-pass factor 'X' lies on the psychrometric chart at the:
A.	Intersection of RSHF line with saturation curve
B.	Intersection of GSHF line with saturation curve
C.	Point which divides RSHF line in proportion to 'X' and \[(1-x)\]
D.	Point which divides ESHF line in proportion to 'X 'and \[(1-x)\]
Answer» E.

Discussion

2090.	If the stream function is given by \[\psi =3xy,\] then the velocity at a point (2, 3) will be:
A.	7.21 unit
B.	10.82 unit
C.	18 unit
D.	54 unit
Answer» C. 18 unit

Discussion

2091.	A 1: 20 model of a spillway dissipates 0.25 hp. The corresponding prototype horsepower dissipated will
A.	0.25
B.	5
C.	447.2
D.	8944.3
Answer» E.

Discussion

2092.	Given power 'P' of a pump, the head 'H' and the discharge 'Q' and the specific weight \['\omega '\] of the liquid, dimensional analysis would lead to the result that 'P' is proportional to:
A.	\[{{H}^{1/2}}\,\,{{Q}^{2}}w\]
B.	\[{{H}^{1/2}}\,\,Q\,w\]
C.	\[H\,{{Q}^{1/2}}\,w\]
D.	\[H\,Q\,w\]
Answer» E.

Discussion

2093.	In a boundary layer developed along the flow, the pressure decreases in the downstream direction. The boundary layer thickness would:
A.	Tend to decrease
B.	Remain constant
C.	Increase rapidly
D.	Increase gradually
Answer» E.

Discussion

2094.	In a fully trubulent flow through a rough pipe, the friction factor \['f'\] is (Re is the Reynolds number and \[{{\xi }_{s}}/D\] is relative roughness):
A.	A function of Re
B.	A function of Re and \[{{\xi }_{s}}/D\]
C.	A function of \[{{\xi }_{s}}/D\]
D.	Independent of Re and \[{{\xi }_{s}}/D\]
Answer» C. A function of \[{{\xi }_{s}}/D\]

Discussion

2095.	The isentropic enthalpy drop in moving blade is two - thirds of the isentropic enthalpy drop in fixed blades of a turbine. The degree of reaction will be:
A.	0.4
B.	0.6
C.	0.66
D.	1.66
Answer» B. 0.6

Discussion

2096.	For a Parson's reaction turbine if a, and \[{{\alpha }_{2}}\] are fix angles at inlet and exit respectively and \[{{\beta }_{1}}\] and \[{{\beta }_{2}}\] are the moving blade angles at entrance and respectively, then:
A.	\[{{\alpha }_{1}}={{\alpha }_{2}}\,\,and\,\,{{\beta }_{1}}={{\beta }_{2}}\]
B.	\[{{\alpha }_{1}}={{\alpha }_{1}}\,\,and\,\,{{\alpha }_{2}}={{\beta }_{2}}\]
C.	\[{{\alpha }_{1}}<{{\beta }_{1}}\,\,and\,\,{{\alpha }_{2}}={{\beta }_{2}}\]
D.	\[{{\alpha }_{1}}={{\beta }_{2}}\,\,and\,\,{{\beta }_{1}}={{\alpha }_{2}}\]
Answer» E.

Discussion

2097.	In an ideal impulse turbine, the:
A.	Absolute velocity at the inlet of moving blade is equal to that at the outlet
B.	Relative velocity at the inlet of the moving blade is equal to that at the outlet
C.	Axial velocity at the inlet is equal to that at the outlet
D.	Whirl velocity at the inlet is equal to that at the outlet
Answer» C. Axial velocity at the inlet is equal to that at the outlet

Discussion

2098.	A single-stage impulse with a diameter of 120 cm runs at 3000 rpm. If the blade speed ratio is 0.42, then the inlet velocity of steam will be:
A.	79 m/s
B.	188 m/s
C.	\[45{}^\circ \]m/s
D.	900 m/s
Answer» D. 900 m/s

Discussion

2099.	The clearance volume of a reciprocating compressor directly affects:
A.	Piston speed
B.	Noise level
C.	Volumetric efficiency
D.	Temperature of air after compression.
Answer» D. Temperature of air after compression.

Discussion

2100.	A multistage compressor is to be designed for a given flow rate pressure ratio. If the compressor consists of axial flow stages followed by centrifugal instead of only axial flow-stages, then the:
A.	Overall diameter would be decreased
B.	Overall diameter would be increased
C.	Axial length of the compressor would be increased
D.	Axial length of the compressor would be decreased.
Answer» C. Axial length of the compressor would be increased

Discussion

Explore topic-wise MCQs in Railways.

Which of the following heating elements can give highest temperature in resistance heating?

The device necessarily used for automatic temperature control in a furnace is

Wound rotor and squirrel-cage motors with high slip which develop maximum torque at stand still are used for

Miniature lamps on automobiles are used for

Ward-Leonard controlled d.c. drives are generally used for

A gas turbine plant working on Joule cycle produces 4000 kW of power. If its work ratio is 40%, what is the power consumed by the compressor?

What is the ratio of the static enthalpy rise in the rotor to the static enthalpy rise in the stage of an axial flow compressor defined as?

Stalling of blades in axial-flow compressor is the phenomenon of:

Compared to axial compressors centrifugal compressors are more suitable for:

The pressure rise in the impeller of centrifugal compressor is achieved by:

The thermal efficiency of a gas turbine cycle with regeneration in terms of \[{{T}_{3}}\] (maximum temperature),\[{{T}_{1}}\] (minimum temperature) \[{{r}_{p}}\] (pressure ratio) and \[k-\left( \frac{{{c}_{p}}}{{{c}_{v}}} \right)\] is given by:

Consider the following statements: The reheat cycle helps to reduce 1. Fuel consumption 2. Steam flow 3. The condenser size Which of these statements are correct?

The efficiency of a simple gas turbine can be improved by using a regenerator, because the:

In an axial flow compressor design, velocity diagrams are constructed from the experimental data of aerofoil cascades. Which one of the, following statements in this regard is correct?

In Centrifugal compressor terminology, vaneless space refers to the space between:

A three-stage Rateau turbine is designed in such a manner that the first two stages develop equal power with identical velocity diagram while the third one develops more with higher blade speed. In such a multistage turbine the blade ring diameter:

Consider the following factors: 1. Cylinder size 2. Clearance ratio 3. Delivery pressure 4. Compressor shaft power. The factors which affect the volumetric efficiency of a single-stage reciprocating air compressor would include:

Which one of the following statements is the?

In a De Laval nozzle expanding superheated steam from 10 bar to 0.1 bar, the pressure as the minimum cross-section will be:

What will be the shape of the velocity triangle at the exit of a radial bladed centrifugal impeller, taking into account slip?

A four-stage compressor with perfect intercooling between stages compresses air from 1 bar to 16 bar. The optimum pressure in the last intercooler will be:

In a two-stage compressor with ideal intercooling, for the work requirement to be minimum, the intermediate pressure \[{{p}_{i}}\] in terms of condenser and evaporator pressure \[{{p}_{c}}\] and \[{{p}_{e}}\] respectively is:

Gas turbine develops 120 kJ of work while the compressor absorbed 60 kJ of work and the heat supplied is 200 kJ. If regenerator which would recover 40% of the heat in the exhaust were used, then the increase in the overall thermal efficiency would be:

Given: \[{{v}_{w\,2}}=\] velocity of whirl at outlet \[{{u}_{2}}=\]Peripheral velocity of the blade tips The degree of reaction in a centrifugal compressor equal to:

Centrifugal compressors are suitable for large discharge and wider mass flow range, but at a relatively low discharge pressure of the order of 10 bars, because of:

Once through boiler is named as such because:

For a multistage compressor, the polytropic efficiency is:

A double acting steam engine with a cylinder diameter of 19 cm and a stroke of 30 cm has a cut-off of 0.35. The expansion ratio for this engine is nearly:

In a centrifugal compressor, the highest Mach number leading to shockwave in the fluid flow occurs at:

Shielding in a nuclear reactor is generally done to protect against:

In a reciprocating air compressor the compression work per kg of air

If (to geometrically similar impellers of a centrifugal compressor are operated at the. same speed, then their head discharge and power will vary with their diameter ratio:

Intercooling in gas turbines:

Performance of a reciprocating Compressor is expressed by:

The state of air supplied by a cooling coil with a by-pass factor 'X' lies on the psychrometric chart at the:

If the stream function is given by \[\psi =3xy,\] then the velocity at a point (2, 3) will be:

A 1: 20 model of a spillway dissipates 0.25 hp. The corresponding prototype horsepower dissipated will

Given power 'P' of a pump, the head 'H' and the discharge 'Q' and the specific weight \['\omega '\] of the liquid, dimensional analysis would lead to the result that 'P' is proportional to:

In a boundary layer developed along the flow, the pressure decreases in the downstream direction. The boundary layer thickness would:

In a fully trubulent flow through a rough pipe, the friction factor \['f'\] is (Re is the Reynolds number and \[{{\xi }_{s}}/D\] is relative roughness):

The isentropic enthalpy drop in moving blade is two - thirds of the isentropic enthalpy drop in fixed blades of a turbine. The degree of reaction will be:

For a Parson's reaction turbine if a, and \[{{\alpha }_{2}}\] are fix angles at inlet and exit respectively and \[{{\beta }_{1}}\] and \[{{\beta }_{2}}\] are the moving blade angles at entrance and respectively, then:

In an ideal impulse turbine, the:

A single-stage impulse with a diameter of 120 cm runs at 3000 rpm. If the blade speed ratio is 0.42, then the inlet velocity of steam will be:

The clearance volume of a reciprocating compressor directly affects:

A multistage compressor is to be designed for a given flow rate pressure ratio. If the compressor consists of axial flow stages followed by centrifugal instead of only axial flow-stages, then the: