Corrections for Relative Humidity

a Using Fig. 1, suggest another suitable hypothesis for the class to investigate. [1] 

 Relative humidity is affected by the type of ground surface/temperature

 Temperature is affected by the type of ground surface

               

b Using Fig. 1, identify the instruments needed in this investigation. [2] 

 Digital thermometer

 Hygrometer/sling psychrometer

1m each 


c Suggest three reasons why temperatures vary around the school campus. [3] 

 Sun: shade from sun/ trees / buildings will cause temperatures to be lower. Areas that has direct sunlight will have higher temperatures.

 Wind: Areas that are exposed to wind will have lower temperatures. Areas that are sheltered from wind and not ventilated will have higher temperatures.

 Different types of surface - Grass surfaces have temperature that are lower as soil and rocks will not absorb heat. Concrete surfaces will absorb heat and therefore have higher temperature.



a) With the aid of Fig. 3, calculate the relative humidity for the following readings:

 Temperature difference = 1°C  Relative Humidity = 91% 


b) Describe the advantages of using a digital thermometer and a hygrometer over a 

maximum-minimum thermometer and a wet and dry bulb thermometer.          [4]              

Any 4 points

 The digital thermometer and hygrometer can give instant readings. Thus, one does 

not have to work out the answer.

 Easy / clear to read with a large digital readout  

 One does not need to learn how to read a thermometer.

 Parallax errors can be avoided since one does not have to read off thermometer.

 Since exact figures are given, the measurements are more accurate.

 Portable / can be used at more than one site 

 Safer to use as there is no mercury content


With reference to Figure 1, describe and explain the relationship between relative humidity and air temperature.     [4]                                                                                                                                                    

Describe [2m]

- As temperature increases, the relative humidity within a parcel of air reduces/As the temperature decreases, the relative humidity within a parcel of air increases. 

OR there is an inverse relationship between temperature and relative humidity

-  For every 10 deg increase in temperature, relative humidity decreases by roughly 50%


Explain [2m]

-  Warm air has the ability to hold more water vapour

- Hence as the parcel of air increases in temperature while the amount of absolute water vapour remains the same, there is an overall decrease in the relative humidity/percentage of air saturated by water vapour



With reference to Fig. 1, identify the instrument used by the students and state the relative humidity recorded for that day.  Explain how the students obtain this information, using evidence from Fig.1.   [5] 

                                                                                                                            

 Instrument used:  wet and dry bulb thermometer / Sling psychrometer 

 Relative humidity recorded: 61% 

 Read/record the dry bulb temperature, which is 33° C

 Read/record the wet bulb temperature, which is 27° C

 Find the wet bulb depression is 6° C