Spot the Differences (14)

IV. Water & Humidity

A. States of water Draw the diagram below: Energy Energy Energy

B. Specific Humidity Amount of water vapor in air. 1. Warm air can hold more water vapor, because its molecules are further apart have more vacancy.

C. Relative Humidity -actual amount of H2O vapor in air (specific humidity) compared to the max. amount the temp. of air can hold.

1. Saturated air has a relative humidity of 100% Relative Humidity for Air at 26.5°C (capacity 22 g) Relative humidity= 5.5/22 = 25% 5.5 g 1. Saturated air has a relative humidity of 100% Relative humidity= 11/22 = 50% Specific Humidity 11 g Relative humidity= 22/22 = 100% 22 g

2. Finding relative humidity= psychrometer (evaporation causes cooling

The “Dry Bulb” Don’t let it fool you. It is just a thermometer. It measures the air temperature. Duh! 20°C

The “Wet Bulb” Has a little wet booty tied to the bottom. Gets cool when water evaporates. 12°C Wet Booty

A Dry Day… A lot of moisture will evaporate. The wet bulb will be a lot cooler than the dry bulb. 20°C 20°C 14°C 12°C 8°C Difference between wet bulb & dry bulb is 12 °C.

A Humid Day… A little bit of moisture will evaporate. The wet bulb will not be much cooler than the dry bulb. 20°C 14°C Difference between wet bulb & dry bulb is 6 °C.

Dry-bulb temperature is your air temperature. 20 °C

Subtract (the difference) between the dry bulb and wet bulb

20°C 14°C 20-14=6

18°C 16°C 18-16=2

Put it all together 20°C 8°C 20-8=12 Relative Humidity = 11%

14°C 10°C 14-10=4 Relative Humidity = 60%

Add to your notes D. Dew point dew- H2O vapor condenses on a surface (ex. Grass, shower, car window) Dew point= temp. at which saturation (specific humidity = capacity) occurs.

15.5 Capacity Vapor Temperature (°C) 10 Capacity Vapor Over capacity = DEW 4.5 Capacity Vapor 0 g 4 g 8 g

The End

Earth Science Lab Get out your composition notebook # 11: Dew Point & Relative Humidity Lab

Post Lab Questions Compare specific humidity vs. relative humidity. What instrument is used to find relative humidity Define dew point in your own terms. The amount of dew decreases during the daytime. Explain why this occurs. (Hint: think about what temperature holds more water and when dew forms.)

Lab Instructions: Copy Data Table A & B pg. 519 (black text) into your comp. book. Do the procedure for Part A & Part B Following instructions PRECISELY Answer 1-3 “Analysis & Conclusion” questions