Which temperature is greater wet bulb temperature or dry bulb temperature and why?
A wet bulb thermometer measures the extent of cooling as moisture dries from a surface (evaporative cooling). The wet bulb temperature is always lower than the dry bulb temperature except when there is 100% relative humidity, making the wet bulb temperature a more accurate measurement of product temperature.
Why do scientists use a wet bulb vs a dry bulb thermometer?
Even healthy people will die rapidly in such conditions. Wet-bulb thermometers allow researchers to work out whether humans can sweat. If the water evaporates, the thermometer cools down, so that ‘wet bulb’ temperatures are lower than ‘dry bulb’ temperatures.
When dry bulb temperature and wet bulb temperature are measured greater the difference between DBT and WBT?
MCQ: When dry bulb temperature (DBT) and wet bulb temperature (WBT) are measured, greater the difference between DBT and WBT, greater the amount of water vapour held in the mixture. smaller the amount of water vapour held in the mixture. same the amount of water vapour held in the mixture.
Why does wet bulb temperature decrease as psychrometer spins?
This happens because evapora- tion has a cooling effect on the wet bulb ther- mometer. The temperature of the wet bulb thermometer will decrease as the instrument is swung until the moisture content of the wet wick reaches equilibrium with that of the sur- rounding air.
What is a wet bulb temperature reading?
Wet bulb temperature is the lowest temperature to which air can be cooled by the evaporation of water into the air at a constant pressure. It is therefore measured by wrapping a wet wick around the bulb of a thermometer and the measured temperature corresponds to the wet bulb temperature.
How does a dry and wet bulb thermometer work?
A dry thermometer has the bulb exposed to air. A wet thermometer has the bulb covered with a muslin cloth which is dipped in water. It is used to measure the relative humidity of temperature. When air is saturated, evaporation stops and the two bulbs show the same reading.
Why is a wet and dry bulb thermometer kept in a Stevenson screen?
All 4 thermometers are mounted inside the Stevenson screen to protect them. Heat is required for evaporation, and in this case, the heat needed to evaporate the water or sublimate the ice will be drawn from the thermometer bulb, making the thermometer read a lower temperature than it would otherwise.
What 2 measurements do you need a wet bulb thermometer to find?
A wet bulb thermometer measures the extent of cooling that happens as moisture dries from a surface (evaporative cooling). The wet bulb temperature is always lower than the dry bulb temperature except when there is 100% relative humidity.
Why is Stevenson’s screen painted white in Colour?
Stevenson screens are always painted white to better reflect the sun’s rays. The louvered sides allow outside air to flow around the thermometers. At some locations, the airflow is assisted by a psychrometer motor that pumps outside air across the instruments inside.
Why should an instrument shelter be painted white?
Whatever paint you use, be sure to keep your shelter painted white to prevent excess heat absorption by the wood. Fading paint exposes the wood frame, allowing heat radiation to be absorbed into the shelter unit & causing temperature readings inside the box to be higher than what is actual ambient air temperature.
How is Stevenson screen useful?
Stevenson screen is used for providing shelter for meteorological instruments, particularly wet and dry bulb thermometers. It is kept 1.25 meters above the ground by legs. It is done so to avoid strong temperature gradients at ground level. Stevenson screen has sides to encourage the free passage of air.
What is inside a Stevenson screen?
It forms part of a standard weather station and holds instruments that may include thermometers (ordinary, maximum/minimum), a hygrometer, a psychrometer, a dewcell, a barometer, and a thermograph. The common type of Stevenson screen has a maximum and minimum thermometer for daily readings.
Which instrument is kept in Stevenson screen?
A barometer can be found in a Stevenson screen. This instrument measures air presure. A maximum and minimum thermometer can also be found in a Stevenson screen. They measure highest and lowest temperatures.
Why does the Stevenson screen have a double roof?
Stevenson screen has a double roof to reduce excessive heat from solar irradiation.
Why is Stevenson screen 1.21 m high above the ground?
It is kept 1.25m/4.1ft (UK standard) above the ground by legs to avoid strong temperature gradients at ground level, has louvred sides to encourage the free passage of air, and is painted white to reflect heat radiation, since what is measured is the temperature of the air in the shade, not of the sunshine.
Where should rain gauge be?
The gauge should be placed on level ground, ideally in a sheltered location with no ground falling away steeply on the windward side. Obstructions such as trees and buildings, which affect local wind flow, should be a distance away from the gauge of at least twice their height above it.