Important Objective Questions On Heat & Welding
1.Which of the following methods of heating is not dependent on the frequency of supply ?
Induction heating
Dielectric heating
Electric resistance heating
All of the above
ANSWER : : Electric resistance heating
2.The material of the heating element for a furnace should have
lower melting point
higher temperature coefficient
high specific resistance
all of the above
ANSWER : : high specific resistance
3.For the transmission of heat from one body to another
temperature of the two bodies must be different
both bodies must be solids
both bodies must be in contact
at least one of the bodies must have some source of heating
ANSWER : : temperature of the two bodies must be different
4.Which of the following will happen if the thickness of refractory wall of furnace is increased ?
Heat loss through furnace wall will increase
Temperature inside the furnace will fall
Temperature on the outer surface of furnace walls will drop
Energy consumption will increase
ANSWER : : Temperature on the outer surface of furnace walls will drop
5.When a body reflects entire radiation incident on it, then it is known as
white body
grey body
black body
transparent body
ANSWER : : white body
6.The process of heat transfer during the reentry of satellites and missiles, at very high speeds, into earth’s atmosphere is known as
ablation
radiation
viscous dissipation
irradiation
ANSWER : : ablation
7.________ has the highest value of thermal conductivity.
Copper
Aluminium
Brass
Steel
ANSWER : : Copper
8.Which of the following insulating materials was suitable for low temperature applications ?
Asbestos paper
Diatomaceous earth
80 percent magnesia
Cork
ANSWER : : Diatomaceous earth
9.By which of the following methods the temperature inside arc nace can be varied ?
By disconnecting some of the heating elements
By varying the operating voltage
By varying the current through heating elements
By any of the above method
ANSWER : : By any of the above method
10.A perfect black body is one that
transmits all incident radiations
absorbs all incident radiations
reflects all incident radiations
absorbs, reflects and transmits all incident radiations
ANSWER : : absorbs all incident radiations
11.Heat transfer by condition will not occur when
bodies are kept in vacuum
bodies are immersed in water
bodies are exposed to thermal radiations
temperatures of the two bodies are identical
ANSWER : : temperatures of the two bodies are identical
12.A non-dimensional number generally associated with natural convection heat transfer is
Prandtl number
Grashoff number
Pecelet number
Nusselt number
ANSWER : : Grashoff number
13.By the use of which of the following, high frequency power supply for induction furnaces can be obtained ?
Coreless transformers
Current transformers
Motor-generator set
Multi-phase transformer
ANSWER : : Motor-generator set
14.Heat is transferred simultaneously by condition, convection and radiation
inside boiler furnaces
during melting of ice
through the surface of the insulted pipe carrying steam
from refrigerator coils to freezer of a refrigerator
ANSWER : : inside boiler furnaces
15.The temperature inside a furnace is usually measured by which of the following ?
Optical pyrometer
Mercury thermometer
Alcohol thermometer
Any of the above
ANSWER : : Optical pyrometer
16.Which of the following heating methods has maximum power factor ?
Arc heating
Dielectric heating
Induction heating
Resistance heating
ANSWER : : Resistance heating
17.In a resistance furnace the atmosphere is
oxidising
deoxidising
reducing
neutral
ANSWER : : oxidising
18.In an electric room heat convector the method of heating used is
arc heating
resistance heating
induction heating
dielectric heating
ANSWER : : resistance heating
19.In induction heating ______ is abnormally high.
phase angle
frequency
current
voltage
ANSWER : : frequency
20.Which of the following has the highest value of thermal conductivity ?
Water
Steam
Solid ice
Melting ice
ANSWER : : Solid ice
21.Induction furnaces are employed for which of the following ?
Heat treatment of castings
Heating of insulators
Melting aluminium
None of the above
ANSWER : : Heat treatment of castings
22.Induction heating process is based on which of the following principles ?
Thermal ion release principle
Nucleate heating principle
Resistance heating principle
Electro-magnetic induction princi�ple
ANSWER : : Electro-magnetic induction princi�ple
23.In resistance heating highest working temperature is obtained from heating elements made of
nickel copper
nichrome
silicon carbide
silver
ANSWER : : silicon carbide
24.Properly of low temperature co-eflficient of heating element is desired due to which of the following reasons ?
To avoid initial rush of current
To avoid change in kW rating with temperature
Both (a) and (b)
Either (a) or (b)
ANSWER : : Both (a) and (b)
25.In heating the ferromagnetic material by induction heating, heat is produced due to
induced current flow through the charge
hysteresis loss taking place below curie temperature
due to hysteresis loss as well as eddy current loss takingplace in the charge
none of the above factors
ANSWER : : due to hysteresis loss as well as eddy current loss takingplace in the charge
26.Which of the following methods is used to control temperature in resistance furnaces ?
Variation of resistance
Variation of voltage
Periodical switching on and off of the supply
All of the above methods
ANSWER : : All of the above methods
27.For radiant heating around 2250�C, the heating elements are made of
copper alloy
carbon
tungsten alloy
stainless steel alloy
ANSWER : : tungsten alloy
28.Hysteresis loss and eddy current loss are used in
induction heating of steel
dielectric heating
induction heating of brass
resistance heating
ANSWER : : induction heating of steel
29.In the indirect resistance heating method, maximum heat-transfer takes place by
radiation
convection
conduction
any of the above
ANSWER : : radiation
30.In arc furnace the function of choke is
to stabilize the arc
to imprpve, power factor
to reduce severity of the surge
none of the above
ANSWER : : to stabilize the arc
31.It is desirable to operate the arc furnaces at power factor of
zero
0.707 lagging
unity
0.707 leading
ANSWER : : 0.707 lagging
32.In direct arc furnace, which of the following has high value ?
Current
Voltage
Power factor
All of the above
ANSWER : : Current
32.Which of the following is an advantage of eddy current heating ?
The amount of heat generated can be controlled accurately
Heat at very high rate can be gene-rated
The area of the surface over which heat is produced can be accurately controlled
All of the above
ANSWER : : All of the above
33.Radiant heating is used for which of the following ?
Annealing of metals
Melting of ferrous metals
Heating of liquids in electric kettle
Drying of paints and varnishes
ANSWER : : Drying of paints and varnishes
34.The electrode of a direct arc furnace is made of
tungsten
graphite
silver
copper
ANSWER : : graphite
35.Direct arc furnaces have which of the following power factors ?
Unity
Low, lagging
Low, leading
Any of the above
ANSWER : : Low, lagging
36.For heating element high resistivity material is chosen to
reduce the length of heating element
increase the life of the heating element
reduce the effect of oxidation
produce large amount of heat
ANSWER : : reduce the length of heating element
37.Radiations from a black body are proportional to
T1
T2
T3
T*
ANSWER : : T*
38.Resistance variation method of temperature control is done by connecting resistance elements in
series
parallel
series-parallel connections
star-delta connections
ANSWER : : all of the above ways
39.Due to which of the following reasons it is desirable to have short arc length ?
To achieve better heating
To increase the life of roof refractory
To have better stirring action
To reduce problem of oxidation
ANSWER : : All of the above
40.Induction heating takes place iitwhich of the following ?
Insulating materials
Conducting materials which are magnetic
Conducting materials which are non-magnetic
Conducting materials which may or may not be magnetic
ANSWER : : Conducting materials which may or may not be magnetic
41.For intermittent work which of the following furnaces is suitable ?
Indirect arc furnace
Core less furnace
Either of the above
None of the above
ANSWER : : Indirect arc furnace
42.Which of the following devices is necessarily required for automatic temperature control in a furnace ?
Thermostat
Thermocouple
Auto-transformer
Heating elements of variable resis-tance material
ANSWER : : Thermocouple
43.In an electric press mica is used
as an insulator
as a device for power factor improvement
for dielectric heating
for induction heating
ANSWER : : as an insulator
44.Ajax Wyatt furnace is started when
it is filled below core level
it is filled above core level
it is fully empty
none of the above
ANSWER : : it is filled above core level