Mixing Ratio and Dew Point materials

This table/chart relates Mixing Ratio, Dew Point, and Temperature.  I calculated the values for Albuquerque’s altitude, but if you live somewhere else it is close enough:mixing ratios

These are some problems about Mixing Ratio and Dew Point.  If any math is required, it is only multiplication.  You might need the chart above.  Other problems are more “thought problems” to see if you get what is going on or not:practice problems with humidity I

Answer Key for above problems:  practice problems with humidity I_KEY

There is also a simple hands-on experiment that you can do to measure the dew point.  Take an empty aluminum soda can and cut the top off.  If small kids are involved you might want to tape the cut edge because it can be sharp.  Fill the can halfway with room-temperature water.  Get a glass thermometer and some ice cubes.  It works best with crushed ice or tiny ice cubes.  Put one single small piece of ice in the can.  Stir it until it completely melts.  When it is gone, put in another, and stir until it completely melts.  As you are doing this, the temperature of the water inside the can is cooling.  If you continue this process, you will eventually cool the surface of the can until it at the dew point*.  When this happens, you will notice condensate starting to form.  You want to catch the temperature at which it first forms – it will be a foggy film at first – not big drops.  Take the temperature of the water at this instant when the condensation first forms, and that temperature is the dew point temperature of the air.

* This ONLY WORKS if the dew point is greater than 0C or 32F!  Otherwise you cannot get the water cold enough to make dew.  If you live in the US you can check the local weather conditions from weather.gov which will give you the current dew point.  For most people, this will not work during the winter because the air is too dry.  But it really depends on where you live.