This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Evaporimeters – Set 2”.
1. As per IS 5973-1970, what is the material requirement for the fixed point gauge of the evaporation pan?
a) Copper
b) Brass
c) Steel
d) Any non-rusting metal
View Answer
Explanation: The fixed point gauge is an attachment used to indicate the level upto which the water needs to be filled and maintained. It should be made of brass and be of the form of a rod of 10 mm diameter.
2. Which of the following thickness is not allowed for the evaporation pan as per IS 5973-1970?
a) 0.9 mm
b) 1.0 mm
c) 1.1 mm
d) 1.2 mm
View Answer
Explanation: The pan should be made from either a copper sheet or a non-rusting, non- magnetic stainless steel sheet. The allowable thickness of the sheet is 1.0±0.1 mm.
3. What is the minimum allowable inner diameter of the stilling well in an evaporimeter as per IS 5973-1970?
a) 95 mm
b) 96 mm
c) 98.5 mm
d) 99.5 mm
View Answer
Explanation: The stilling well should be made from a brass tube of 102 mm outer diameter and a wall thickness of 3.0±0.5 mm. So, the maximum thickness tube will give the minimum internal diameter. Therefore, using a tube of thickness 3.5 mm, the internal diameter will be (102 – 2*3.5) = 95 mm.
4. Given below are descriptions for four different evaporation pans A, B, C and D. Which of the following pans meets the requirements of IS-5973-1970?
a) Pan A: copper sheet, 1-piece bottom, 2-piece side, tinned outside, painted white inside
b) Pan B: copper sheet, 2-piece bottom, 2-piece side, tinned inside, painted white outside
c) Pan C: copper sheet, 1-piece bottom, 3-piece side, tinned inside, painted white outside
d) Pan D: brass sheet. 1-piece bottom, 1-piece side, tinned inside, painted white outside
View Answer
Explanation: The pan should be made of copper or stainless steel sheet. The bottom should be fabricated from one piece and the side should be fabricated from not more than three pieces. The inner surface should be tinned uniformly, and the outer surface should be painted with three coats of chlorinated white paint. Pan C is the only pan meeting the above specifications.
5. What is the permitted tolerance on the inner diameter of the ISI standard evaporation pan?
a) ±0.5 mm
b) ±1 mm
c) ±2 mm
d) ±3 mm
View Answer
Explanation: The ISI standard pan is circular in cross section of diameter 1220±3 mm and a depth of 225mm. The tolerance of 3 mm is considered keeping in mind the difficulty in fabricating the side of the pan.
6. Which of the following is the correct description for the wooden platform as per IS 5973-1970?
a) Square of side 1225 mm
b) Square of side 1250 mm
c) Circle of diameter 1225 mm
d) Circle of diameter 1250 mm
View Answer
Explanation: The wooden base platform is a square of sides 1225 mm and height of 100 mm over which the pan shall be placed in a levelled manner without any wobbling. The size of the base is decided based on the maximum allowable outer diameter of the evaporation pan.
7. How many plank pieces are used for fabricating the wooden platform for the pan as per IS 5973-1970?
a) 8
b) 9
c) 10
d) 12
View Answer
Explanation: There are a total of 9 bars used as shown in the figure. The bottom four bars are stacked lengthwise on the thinner face (25 mm) at 400 mm c/c. On top of them, five bars are placed lengthwise on the broader face (75 mm) at 287.5 mm c/c. This gives the platform a total height of (75+25)=100 mm.
8. The Colorado sunken evaporation pan is a cube of side 3 feet.
a) True
b) False
View Answer
Explanation: The Colorado sunken pan is square in plan view with side of 3 feet (920 mm) and a depth of 1.5 feet (460 mm). It has a cuboidal shape and is made up of unpainted galvanized iron sheet.
9. Which of the following is not associated with Colorado sunken pan?
a) It is buried in the ground
b) It has similar radiation characteristics to a lake
c) It is easy to detect any leaks
d) It is expensive to install
View Answer
Explanation: As the name suggests, the Colorado sunken pan is installed by burying it into the ground which makes it expensive compared to other pans. Since the bottom and major part of the sides are beneath the ground level, it becomes difficult to detect and repair any leaks in this pan.
10. What was the main objective for developing the US geological survey floating pan?
a) To achieve similar aerodynamic characteristics as that of the lake
b) To replicate the characteristics of a large water body
c) For easier detection of leaks
d) To avoid digging of the ground surface
View Answer
Explanation: The US geological survey floating pan was developed with an aim to mimic the actual lake features, like radiation characteristics, temperature, wind data, etc. as close as possible so as to get a more accurate idea of the evaporation of the water body.
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