Silicon crystal can be converted to p-type semiconductor by doping with
Phosphorous
Nitrogen
Carbon
Boron
Correct Answer :
D. Boron
Related Questions
Which of the following is not used as a bearing material?
Copper-lead alloys
Babbitts
Bronzes
Cermets
Heating of ferromagnetic materials to a temperature above Curie temperature makes it
Insulator for heat & electricity transmission
Ferritic
Behave like paramagnetic materials
Superconductor
Work hardenable alloy steel used to make the bucket wheel excavators, blades of bulldozers and other earth moving equipments contain iron, carbon and
Manganese
Silicon
Nickel
Chromium
A spring material should have low
Elastic limit
Deflection value
Fatigue resistance
None of these
Which of the following metals is not subjected to electrolytic refining/purification?
Copper
Zinc
Tin
Aluminium
The softness or hardness of a grinding wheel depends upon the type & amount of bonding material used. For general purpose cutter grinding __________ grinding wheel is normally used.
Hard
Soft
Silicon carbide
Aluminium oxide
Diameter of the rivet to be provided on a 20 mm. thick boiler plate will be __________ mm.
10
20
30
40
Identify the false statement
Martensitic steels are less susceptible to pitting corrosion than austenitic steels
Pitting corrosion is usually very localised
Hydrogen embrittlement is facilitated by tensile stress
Stress corrosion cracking is facilitated by tensile stress
Thermit welding uses the following energy source.
Electrical energy
Chemical energy
Energy of high velocity electrons
Heat generated by friction
Out of the following __________ iron has the best capability to bear sudden & excessive shocks.
White
Cast
Wrought
Pig
Force between the molecules of the same substance is called __________ force.
Adhesive
Cohesive
Molecular
Vander Walls
The materials which fracture even at small strains are termed as brittle, while those materials which exhibit an appreciable deformation before failure are termed as
Rigid
Tough
Ductile
Plastic
The process of removal of scale formed during hot rolling of steel is termed as
Descaling
Shot blasting
Pickling
Skimming
__________ remains constant during the adiabatic cooling of moist air.
Wet bulb temperature
Dry bulb temperature
Relative humidity
Specific humidity
A material being tested for endurance strength is subjected to the __________ load.
Impact
Completely reversed
Dynamic
Static & dynamic
__________ pipe is the most suitable for carrying sanitary drainage.
Stainless steel
Reinforced cement concrete
Cast iron
Asbestos cement
Which of the following is the correct nature of shear stress distribution along the cross section in a horizontal circular pipe under steady state fluid flow condition?
Colour comparator is used to measure the
pH value
Electrode potential
Colour intensity
None of these
Property responsible for the talcum powder to cling to the skin is the
Capillary action
Adhesion
Cohesion
Surface tension
Steels with high carbon equivalent have poor Weldability, because in these steels during welding
Carbon and other alloying elements get oxidised from the weld pool
Excessive ferrite forms in the heat affected zone leading to poor toughness of the weld
Martensite forms in the heat affected zone leading to poor toughness/ductility of the weld
Segregation of carbon and other element occurs in the weld pool leading to poor properties of the weld
__________ stress cannot be sustained by a fluid in equilibrium.
Shear
Tensile
Compressive
None of these
The condition of diffraction from a crystal is given by
nλ = 2d Sin θ
λ = d Sin 2θ
λ = 2d Sin 2θ
nλ = d Sin θ
Pick out the correct statement about the condensation.
Filmwise condensation gives a lower heat transfer rate than the dropwise condensation
Suitable coating or vapour additive is used to promote film wise condensation
If a condensing liquid does not wet the surface dropwise, even then condensation will take place on it
Reynolds number of condensing liquid is based on its mass flow rate
The best lubricants for a machine working at high temperature & load is
Grease
Solid lubricant
Animal oils
Mineral oils
Cast iron contains __________ percent carbon.
2.5
3.75
4.75
5.25
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
The pressure outside a bubble/droplet of liquid is __________ the internal pressure.
Greater than
Less than
Equal to
Unpredictable; depends on the bubble size
Lead is added to 60:40 brass primarily to improve
Machinability
Corrosion resistance
Fluidity
Strength
Two solutions A1 & A2 have pH value of 2 & 6 respectively. It implies that the solution
A1 is more alkaline than solution A2
A1 is highly acidic
A2 is very slightly acidic
Both (B) & (C)
In a good rimming steel
Carbon and silicon should be low
Silicon should be low but carbon should be high
Both silicon & carbon should be high
Silicon should be high but carbon should be low