1.Why does everything appear blue in underwater videos of sea turtles or sharks or coral reefs...

1.Why does everything appear blue in underwater videos of sea turtles or sharks or coral reefs or SCUBA divers?

2. Thinking about predation, why would it not matter if shrimp living at a depth of 40 meters have a red carapace?

3. Using a refractometer, what would you expect the salinity to be (ppt) in our:

a. freshwater aquarium

b. saltwater aquarium

4. We often use a barometer to measure atmospheric pressure. Why do we care about atmospheric pressure? What is the English unit for barometric pressure? What is the metric unit for atmospheric pressure?

5. Describe how a sling psychrometer measures relative humidity. In order to read the chart correctly we need to know the air temperature. Why is this important?  

6. If we are interested in measuring the temperature of a surface, we can use a non-contact IR thermometer. How does this instrument work?

Homework Answers

Answer #1


Everything appear blue because red, orange and yellow (long wavelength light) are absorbed more strongly by water than is blue (short wavelength light). So when white light from the sun enters the ocean, it is mostly the blue that gets returned. Same reason the sky is blue."


Salinity is a measurement of a mass of salt in a mass of water and therefore does not vary with temperature however a refractometer does not measure salinity directly but measures the refractive index which is then displayed as salinity .

a) The "Specific Gravity" measured with a standard marine aquarium hydrometer should be between 1.005 and 1.009 or 7 to 13 ppt. If treating for anchorworms closer to 1.009 would be best. This level of salt needs to be maintained for at least 3 weeks. Not all freshwater fish can tolerate this much salt.

b) Recommended salinity levels for a reef salt water aquarium are 1.024 – 1.025 (32 – 33 ppt) and if you are slightly below or above that level (1.022 – 1.027), your tank will be just fine .


atmospheric Pressure has important effects on water chemistry and weather conditions.For instance, more oxygen is dissolved in water at sea level than at high altitudes. High barometric pressure supports sunny, clear, and favorable weather conditions, but lower levels promotes rainy and cloudy weather conditions.

english unit: atm

metric unit : pascal ,1 atm =101325 Pa


A sling psychrometer can be used to find relative humidity, which is expressed as a percentage. It is computed by multiplying the amount of moisture in the air at a given temperature, dividing by the maxi- mum amount of moisture the air could contain at that same temperature, and then multiplying the quotient by 100.

Relative humidity is refer to the amount if water vaspor in the air at a given temperature as a percentage of the maximum amount of water that air can hold at this temperature.So air temperature is important to determined.


Infrared thermometers measure temperature from a distance. This distance can be many miles or a fraction of an inch.

Infrared light works like visible light--it can be focused, reflected or absorbed. Infrared thermometers usually use a lens to focus infrared light from one object onto a detector called a thermopile. The thermopile absorbs the infrared radiation and turns it into heat. The more infrared energy, the hotter the thermopile gets. This heat is turned into electricity. The electricity is sent to a detector, which uses it to determine the temperature of whatever the thermometer is pointed at. The more electricity, the hotter the object is.

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