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121.

The area of the openings in screens should be such that the velocity of flow through them does not exceed

A.	0.75 to 1 m/s	B.	1.5 to 3 m/s
C.	3 to 5 m/s	D.	5 to 6 m/s

122.

Plain sedimentation is a process of retaining water in a basin so that the suspended particles settles down as a result of the

A.	action of sun-rays	B.	action of gravity and forces
C.	action of velocity of the particles	D.	none of these

123.

The rate of settling of a particle in water depends upon the

A.	viscosity of water	B.	density of water
C.	specific gravity of particle	D.	all of these

124.

The particle will settle down more rapidly in water at high temperatures than at lower temperatures.

True

False

125.

The detention time for an ordinary plain sedimentation tank is

A.	1 to 2 hours	B.	2 to 4 hours
C.	6 to 8 hours	D.	20 to 24 hours

126.

In a plain sedimentation tank, under normal conditions, impurities are removed upto

A.	50%	B.	60%
C.	70%	D.	80%

127.

In the design of a sedimentation tank, the essential factor to be considered is

A.	period of detention	B.	sludge capacity
C.	velocity of flow	D.	all of these

128.

The velocity of flow in any sedimentation tank should not exceed

A.	0.05 mm/s	B.	0.5 mm/s
C.	5 mm/s	D.	50 mm/s

129.

The process of adding certain chemicals to water in order to form flocculent precipitate for absorbing and entraining colloidal mater is called sedimentation with coagulation.

Agree

Disagree

130.

The length of rectangular sedimentation tank should not be more than

A.	twice	B.	three times
C.	four times	D.	six times