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DIY Hygrometer
A hygrometer is more commonly known as a wet and dry bulb thermometer, and is used to find the humidity of the air.You will need:
- Clean, empty 1 pint milk/ soup carton or similar
- Two small thermometers (e.g. bath or fish tank thermometers.)
- Clear sellotape
- water
- Tubular cotton shoe lace, gauze or cotton wool ball
- String ( 60cm - 1m)
What to do
- Cut a piece of shoelace about 3cm long and pull it over the bulb of one
thermometer. Tie it in place so that it won't fall off. Soak the shoelace,
and tape the thermometer to one side of the carton.
- Tape the other thermometer
to the other side of the carton.
- Punch two holes in the top of the carton
(where the lid comes together), thread a long piece of string through the
holes and tie its ends together, to form a loop.
- Go outside and swing the
carton overhead for 1 minute.
- Quickly look at the temperatures on the two
thermometers and write them down. You should find that the 'wet bulb' thermometer
shows a lower reading than the 'dry bulb' thermometer. This is because water
evaporating from the shoelace is cooling the wet bulb thermometer down. The
easier it is for water to evaporate, the bigger the difference between the
two thermometers and the drier the air. You can convert the two readings
into a relative humidity by entering your values into the converter at http://www.srh.noaa.gov/elp/wxcalc/wetbulb.shtml (note
the relative humidity is not very dependent on pressure - if you do not know
the air pressure, just enter 1000millibars)
- Try measuring the humidity
in a bathroom before and after someone has a shower or bath!
Find out more:
Find the current and forecast relative humidity where you are on the BBC website: http://www.bbc.co.uk/weather/5day.shtml?id=3190