Humidity

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Humidity
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Does water have to boil in order to evaporate?
No
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• Boiling water will cause it to evaporate quickly,
  but its not the only way to boil water
• What would happen to a glass of water if left on
  the counter for a few days?

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Where does the water go?

• Water can and will evaporate into the atmosphere
  when we add thermal energy, but is there a limit
  as to how much water can be evaporated?
• How much water vapour can the atmosphere hold?

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Terms

• Saturated as much water vapour in the air as
  possible at a given temperature
• Unsaturated more water vapour could be put into
  the air

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• When water vapour condenses it will return back
  to a liquid state as water droplets.
• This can happen if water loses thermal energy

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Help

• Very small particles in the air will help water
  molecules join together to eventually turn into
  water droplets

We call these particles condensation nuclei
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• How much water vapour in the air at any given
  time is called humidity
• Absolute humidity how much water vapour is in
  the air expressed in grams (g)
• Relative Humidity percentage () of water
  vapour in the air compared to the actual amount
  of water vapour that the air would hold if it
  were saturated

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Calculating relative humidity

• The temperature is 32 ºC
• At this temperature the air can hold 27.7 g of
  water vapour in 1.0 kg of air
• There is currently 14 g of water vapour for each
  kg of air

51
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What can hold more water?

• Warm Air

• Cold Air

When would water vapour condense faster?
When do you notice that the air is dryer?
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• Warm Air
• 24 ºC
• 8 g of water vapour/kg

• Cold Air
• 4 ºC
• 8 g of water vapour/kg

Relative Humidity 42
Relative Humidity 157
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So why do you feel more humidity in the summer?

• Warm air can hold more water vapour before it
  turns into precipitation