A semi-conductor is damaged & behaves like a conductor, on passing a strong electric current through it, because it heats up the crystals & breaks the covalent bonds resulting in __________ electrons.
Lack of free
Excess of
Decrease in
None of these
Correct Answer :
B. Excess of
Related Questions
At the point of boundary layer separation in fluid flow, the
Shear stress is maximum
Velocity gradient is flat
Density variation is maximum
Shear stress is zero
Minimum number of members required to form a Public Limited Joint Stock Com-pany is
7
10
12
17
What happens, when SO2 is passed through a solution of H2S in water?
Precipitation of sulphur takes place
H2SO3 is formed
Oleum is formed
None of these
Which of the following fastening devices has its both ends threaded?
Bolt
Stud
Set screw
Split nut
Pick out the wrong statement about coating/electroplating of metals.
Phosphate coating is used as an excellent base for paints & enamels
Phosphate coating is less corrosion resistant than chromate coating
The base metal to be electroplated is normally made the cathode of the electrolytic cell and coating metal is made the anode
Calorising is the process of coating steel with chromium
The most important function of a washer is to provide bearing area and washers are normally specified by their hole diameters. The diameter of washer as compared to the nut is
More
Less
Same
More but less than the diameter of bolt
Plastics as a material of construction suffer from the drawback of low
Machinability
Density
Strength
Plastic deformation
Silicon crystal can be converted to p-type semiconductor by doping with
Phosphorous
Nitrogen
Carbon
Boron
Tin based white metals are used, where bearings are subjected to
High pressure & load
Low pressure & load
High temperature
Large surface wear
Out of the following, the most malleable material is
Copper
Aluminium
Wrought iron
Lead
Basic open hearth furnace (BOF) is not used for producing __________ steel.
Killed
Rimming
High alloy
None of these
Spark plug is provided in a/an
Engine having carburettor
Diesel engine
Compression ignition engine
Both (B) & (C)
Use of water as a manometric liquid suffers from the disadvantage of its
Low vapour pressure
Corrosive nature
High vapour pressure
High boiling point
The main constituent of bones is
CaF2
Ca3(PO4)2
CaCO3
CaCl2
If the head is doubled in & centrifugal pump, the power required will increase in the ratio of
23
23/2
25/2
21/3
The noble metals
Are exemplified by Na, K and Li
Do not resist corrosion very strongly
Are the lowermost in the electro-chemical series of metals
None of these
To counteract the bad effects of strain hardening on a cold formed part, it must be
Tempered
Normalised
Annealed
Hardened
The usual energy consumption in electric arc furnace steel making is __________ KWh/ton of steel.
60 - 100
400 - 700
1200 -1500
2000 - 2300
Drossing is a __________ operation.
Smelting
Dressing
Roasting
Dressing
The dimensional formula of bulk modulus of elasticity is same as that of the
Pressure
Density
Force
None of these
Pick out the wrong statement about nucleate boiling.
Bubble generation is by expansion of entrapped gas/vapour at small cavities in the surface
Surface temperature is greater than the saturation temperature of the liquid
Heat transfer from the surface of the liquid is less than that in film boiling
The temperature is less than that of film boiling
Which of the following parameters is not responsible for the heat loss from a hot steam carrying bare pipe surface located in a room without fans?
Emissivity of pipe surface
Diameter & length of the pipe
Temperature of hot pipe surface & that of air in the room
None of these
The majority charge carriers in p-type silicon are
Free electrons
Ions
Conduction electrons
Holes
An alloy of Fe - 0.4 % C is
Cast iron
Hypo-eutectoid steel
Hyper-eutectoid steel
Eutectoid steel
Steel rods are normally used for concrete reinforcement because concrete and steel have almost equal
Tensile strength
Compressive strength
Young's modulus
Thermal co-efficient of expansion
Screws are specified by their __________ diameters.
Minor
Major
Pitch
None of these
Out of the following, the best material capable of withstanding shock & vibration without the danger of cracking is
Malleable iron
Grey cast iron
Chilled cast iron
White cast iron
__________ pipe is the most suitable for carrying sanitary drainage.
Stainless steel
Reinforced cement concrete
Cast iron
Asbestos cement
Percentage of argon (by volume) in dry atmospheric air is about
0.09
0.3
0.57
0.94
The 'transition temperature' for ductile to brittle behaviour of steel increases with increase in the __________ content in steel.
Carbon
Manganese
Both 'a' nor 'b'
Neither 'a' nor 'b'