WorksheetsDAY 45-NOV5-DIPLOMA-OCH-ECONOMCIAL SECTION
Total questions: 15
Worksheet time: 13mins
A channel section is said to be most economical when —
A) Area is maximum for a given discharge
B) Wetted perimeter is maximum for a given discharge
C) Wetted perimeter is minimum for a given area
D) Hydraulic gradient is maximum
(a)
For a rectangular channel, the most economical condition is —
A) Depth = Width
B) Depth = ½ Width
C) Width = 2 × Depth
D) Hydraulic radius = ¼ Width
(a)
For maximum discharge in a rectangular channel, the ratio of hydraulic radius to depth is —
A) 0.25
B) 0.333
C) 0.5
D) 0.707
A: A rectangular channel section is most economical when its width is twice the depth.
R: This condition gives maximum hydraulic radius for a given area.
A) Both A and R are true, and R is the correct explanation
B) Both A and R are true, but R is not the correct explanation
C) A is true, R is false
D) Both false
A: The discharge through an open channel is maximum when the wetted perimeter is maximum for a given area.
R: Less wetted perimeter means lower boundary resistance and hence higher velocity.
A true and R true, R is the correct explanation for A
A true and R true, R is not the correct explanation for A
A true and R false
A false and R true
Which among these statements are true?
A: In a circular channel, maximum discharge occurs when it is running half full.
R: At half full, the area and wetted perimeter are both maximum.
(a)
Match the following
Minimum cost
Minimum wetted perimeter
Maximum discharge
Maximum A × R^(2/3)
Maximum velocity
Maximum R for given A
Hydraulic efficiency
Maximum A/P
Match the following Sections with the criteria for most economical section
Rectangular
b = 2y
Trapezoidal
Half top width = sloping side
Triangular
θ = 60°
Circular
θ = 240°
At the most economical condition for a circular channel, the depth of flow = ?
A) 0.81 × diameter
B) 0.95 × diameter
C) 0.5 × diameter
D) Equal to diameter
(a)
For a given discharge, the circular channel will be most economical when the central angle (θ) in radians is —
A) 120°
B) 90°
C) 4π/3
D) 257°
(a)
In a most economical triangular channel, the vertex angle between sides is —
A) 30°
B) 45°
C) 60°
D) 90°
(a)
Which among these statements are false?
A: The hydraulic efficiency of a circular channel is maximum when it runs half full.
R: At half full, both area and wetted perimeter are optimal.
(a)
If wetted perimeter is reduced while keeping area constant, discharge increases for same slope and n.
In all most economical sections, the ratio of area to wetted perimeter (A/P) is maximum.
For a trapezoidal channel with side slopes 1H:1V and θ = 45°, the section is most economical.
