The applications of selenium rectifiers are usually limited to potential of

In selenium rectifiers efficiencies ranging from ______ to ______ percent are attainable

A

25, 35

B

40, 50

C

60, 70

D

75, 85

The metal rectifiers are preferred to valve rectifiers due to which of the following advantages ?

A

They are mechanically strong

B

They do not require any voltage for filament heating

C

Both (A) and (B)

D

None of the above

The metal rectifiers, as compared to mercury arc rectifiers

A

operate on low temperatures

B

can operate on high voltages

C

can operate on heavy loads

D

give poor regulation

E

none of the above

In mercury arc rectifiers having grid, the arc can be struck between anode and cathode only when the grid attains a certain potential, this potential being known as

A

maximum grid voltage

B

critical grid voltage

C

any of the above

D

none of the above

Glass rectifiers are usually made into units capable of D.C. output (maximum continuous rating) of

A

100 A at 100 V

B

200 A at 200 V

C

300 A at 300 V

D

400 A at 400 V

E

500 A at 500 V

A recent study shows that selenium , a mineral →bfound in in seafood, →cis linked to →dreducethe human cancer risk

A

a

B

b

C

c

D

d

Selenium is _____ semiconductor.

A

Extrnisic

B

Intmisic

C

N-type

D

P-type

Ageing of a selenium rectifier may change the output voltage by

A

5 to 10 per cent

B

15 to 20 per cent

C

25 to 30 per cent

D

none of the above

Selenium rectifier can be operated at temperatures as high as

A

25°C

B

40°C

C

60°C

D

75°C

Mercury, in arc rectifiers, is chosen for cathode because

A

Its ionization potential is relatively low

B

Its atomic weight is quite high

C

Its boiling point and specific heat are low

D

All of the above

The applications of selenium rectifiers are usually limited to potential of

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