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

Copper oxide rectifier is usually designed not to operate above___________?

A. 10°c
B. 20°c
C. 30°c
D. 45°c

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

The efficiency of the copper oxide rectifier seldom exceeds____________?

A. 90 to 95%
B. 85 to 90%
C. 80 to 85%
D. 65 to 75%

Selenium rectifier can be operated at temperatures as high as____________?

A. 25°c
B. 40°c
C. 60°c
D. 75°c

The applications of selenium rectifiers are usually limited to potential of_____________?

A. 10 v
B. 30 v
C. 60 v
D. 100 v

In selenium rectifiers efficiencies ranging from _______ to _______ percent are attainable?

A. 25, 35
B. 40, 50
C. 60, 70
D. 75, 85

A commutating rectifier consists of commutator driven by___________?

A. An induction motor
B. A synchronous motor
C. A d.c. series motor
D. A d.c. shunt motor

In a mercury arc rectifier, the anode is usually made of_____________?

A. Copper
B. Aluminium
C. Silver
D. Graphite

Which of the following rectifiers have been used extensively in supplying direct current for electroplating ?

A. Copper oxide rectifiers
B. Selenium rectifiers
C. Mercury arc rectifiers
D. Mechanical rectifiers