The heated parts of an electrical machine dissipate heat into their surroundings by which of the following modes of heat dissipation ?

A. Conduction
B. Convection
C. Radiation
D. All of the above

The noise produced by a ___________ cooled machine is less as the rotor moves in a medium of smaller density?

A. Air
B. Hydrogen
C. Either a. or b.
D. None of the above

The thermal conductivity of hydrogen is _____________ times that of air?

A. 2
B. 3
C. 5
D. 7

cooling is the process of dissipating the armature and field winding losses to a cooling medium circulating within the winding insulation wall______________?

A. Direct
B. Indirect
C. Conventional
D. Any of the above

With conventional hydrogen cooling it is possible to increase the rating of a single unit to___________?

A. 50 mw
B. 100 mw
C. 200 mw
D. None of the above

Hydrogen has a heat transfer co-efficient __________ times that of air?

A. 1.5
B. 2.5
C. 3.5
D. 4.5

Multiple inlet system of air cooling of turbo-alternators can be used for machines of rating upto_______________?

A. 10 mw
B. 30 mw
C. 60 mw
D. 150 mw

The mcrease in heat dissipation by air blasts is due to increase in______________?

A. Conduction
B. Convection
E. Radiation
D. Any ofthe above

On which of the following variables heat convected depends ?

A. power density
B. temperature difference between heated surface and coolant
C. thermal resistivity, density, specific heat
D. gravitational constant

Which of the following materials is used in the manufacture of resistance grids to be used in the starters of large motors ?

A. Copper
B. Aluminium
C. Steel
D. Cast-iron