This set of Engineering Hydrology Multiple Choice Questions & Answers (MCQs) focuses on “Evaporimeters”.
1. Which of the following is not used to estimate the amount of evaporation?
a) Evaporimeters
b) Empirical equations
c) Analytical methods
d) Field plots
View Answer
Explanation: The estimation of the exact amount of evaporation from a body is very difficult. However, evaporimeters, empirical evaporation equations and some analytical methods help us in finding the evaporation to a fairly accurate value.
2. Which of the following instruments is used to measure evaporation?
a) Evaporimeter
b) Lysimeter
c) Potometer
d) Hygrometer
View Answer
Explanation: Evaporimeters are basically pans which contain a measured amount of water, that are exposed to the atmosphere and the reduction of water level due to evaporation is measured and used to obtain the evaporation from nearby water body.
3. Which of the following instruments is not used for measuring evaporation of some form?
a) Atmometer
b) Evaporation pan
c) Atmidometer
d) Tipping bucket
View Answer
Explanation: Tipping bucket is a mechanism employed in rain gauges to measure the rainfall at a point. Atmometer are devices used to measure the evaporation from a wet surface. Atmidometer is a similar instrument and can be used for ice and snow surfaces also.
4. Which of the following is a type of evaporation pan?
a) Class A
b) Class B
c) Class C
d) Class D
View Answer
Explanation: The Class A evaporation pan is a standard evaporimeter used by the US National Weather Service. It is usually made out of unpainted galvanized iron sheets.
5. What is the shape of a Class A evaporation pan?
a) Sphere
b) Frustum
c) Cylinder
d) Cube
View Answer
Explanation: The Class A evaporation pan is circular in plan view with a diameter of 47.5 inches and a height of 10 inches making it cylindrical in shape.
6. A Class A evaporation pan needs to be filled upto 2 inches from the top. How many fillings of a 10 litre bucket would it take to fill up the pan? Assume no spilling and take 1 inch = 2.5 cm.
a) 22
b) 23
c) 44
d) 45
View Answer
Explanation: The volume of water that needs to be filled is,
V=\(\frac{π*d^2*h}{4}=\frac{π*(47.5 in)^2*((10-2)in)}{4}=\frac{π*(118.75 cm)^2*(20 cm)}{4} \) =221506.83cm3=221.5 L
Now, since 10 litre fillings are used to fill the pan, the number of times the bucket needs to be filled is, (221.5 / 10) = 22.15 ≈ 23 times.
7. Which of the following specifies the correct positioning of a class A evaporation pan?
a) On the ground surface
b) Above the ground surface
c) Below the ground surface
d) Over the water surface
View Answer
Explanation: The evaporation pan is placed on a levelled wooden base platform of height around 15 cm above the ground level. This to allow free circulation of air below the pan and to prevent the animals from drinking from it.
8. The evaporation from a screened pan is found to be more compared to that from an unscreened pan.
a) True
b) False
View Answer
Explanation: The evaporation from a screened pan is found to be less (by ≈14%) compared to an unscreened pan. This is because the wire mesh prevents the loss of water due to birds and also keeps the water temperature more uniform during the day and night.
9. Which of the following Indian Standards gives the specifications for ISI standard pan?
a) IS 3912
b) IS 8389
c) IS 6939
d) IS 5973
View Answer
Explanation: The IS 5973 code gives the specifications for pan evaporimeter also known as modified Class A pan. The standards IS 3912, IS 8389 and IS 6939 give the functional requirements of sounding rods, guidelines for use of recording rain gauges and methods for determination of evaporation from reservoirs, respectively.
10. Which of the following is not a requirement of the pan evaporimeter as per IS 5973-1970?
a) Solid steel cover
b) Fixed point gauge
c) Thermometer with clamp
d) Anemometer
View Answer
Explanation: The pan evaporimeter, as per the requirements of IS 5973-1970, should consist of a pan, wire mesh cover, fixed point gauge, thermometer with clamp, measuring cylinder, a totalizing anemometer and a wooden platform.
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