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PHY 1600 Exam 1
Terms in this set (61)
the study of the effects of work, heat, and energy on a system
a measurement of the average speed, kinetic energy, or movement of molecules
How do we measure temperature?
thermal expansion of liquid (liquid filled mercury thermometer will expand as temp. rises), thermal expansion of a solid, voltage between 2 metals-thermocouple , resistance-thermister, Infrared Thermometer
How can you calibrate your food thermometer?
Ice water method (very reliable) and boiling water method
what is the wavelength of radiation when something hot or cold?
Hot = has a short wavelength
Cold = has a longer wavelength
is an indication of how ACCURATE an IR reading will be of the actual surface temperature, hard with shiny surfaces,
High emissivity = (close to 1) Accurate
Low Emissivity= (close to 0) inaccurate <-- can put oil or scotch tape on it to get the correct reading
Common Temperature Scales
Celsius (relative) --> boiling = 100, room temp. 21, freezing = 0
Fahrenheit (relative) --> boiling = 212, room temp. = 69.8, freezing = 32
Kelvin (absolute) --> boiling = 373.15, room temp. 294.15, freezing = 273.15
Rankine (absolute) --> boiling = 671.67, room temp = 529.47, freezing = 491.67
What scale is Kelvin based on? What is Rankine based on?
Kelvin - Celcius
Rankine - Fahrenheit
Equations: Celcius to Fahrenheit & Fahrenheit to celsius
Celcius to fahrenheit: (C X 9/5) + 32 = F
Fahrenheit to celcius: (F - 32) X 9/5 = C
What are the differences in temperature for C and F?
1C & 1.8F
When do proteins coagulate and cooking begins?
Water boils at what temperature?
What temp. is the Maillard reactions of sugars?
What temp. is the beginning of the caramelization of sugars?
What temp. is the best for sautee and frying?
are a series of browning reactions that occur when certain sugars react with the amino acids found in proteins, what we like in crispy steak
is the process where sugars react with sugars in the presence of high heat but without the proteins
Increasing the __________ increases the _____ of reaction
Reactions happen slower in ______ temperatures.
Rule of thumb for for cooking
cooking = time X temperature
What is the most important variable in cooking?
the temperature of the food, NOT the temperature of the environment in which it's being cooked (the temperature on the oven will determine the rate, in which the food temperature will increase which then alters the rate in reaction the food
Where is all the water on Earth?
most in saltwater, in oceans, in the Pacific
- freshwater most is ice and snow
-surface water is mostly from freshwater lakes, mostly in amazon river
Most fruits and vegetables are more than ___ of water?
80% water by weight
H2O, 104.45 angle between both hydrogens, Hydrogen and oxygen are held together by covalent bonds, H2O is a polar molecule
molecules that stay close together
molecules that don't stay together
the amount of heat required to change the temperature of a certain mass of a substance
- there's an equation
Water requires... and is....
require an enormous amount of energy to change its temperature, impressively thermally sluggish
What is waters specific heat? Cooking oils specific heat?
water - 4,186 J/(kgC); Cooking oil - about 1,800 J/KgC
we can cook many things with no additional heat input once water is boiling, them temp. will stay near boiling for a long time, can do passive cooking for pasta oats instant rice (white or brown)
Things to do when cooking with water considering energy:
only heat as much water as needed, avoid using hot water if not necessary (washing hands), use the same pot of boiling water for multiple purposes (steam veggies then look pasta for ex)
Phase Change Diagram
the amount of heat it takes to change phases
Heat of Vaporization
2260 Kj/Kg --> liquid to vaporization
Latent heat of fusion formation
334 KJ/Kg --> solid to liquid
- may be tint crevices on a rough surface or rough particles introduced into the solution
- salt adds nucleation sites
When there aren't nucleation sites are necessary to initiate phase change
Sub-cooled water (it doesn't actually freeze until it is shaken or there's a bubble or disturbance), super heated water (water hotter than the boiling point)
The Leidenfrost Effect
is all about evaporation, if a pan is hotter the water would stay in tact longer than a colder pan where it evaporates quicker, it's so hot it rides on a bed of steam (this is how you know when to sear something)
Adding salt (lowers or raises) the freezing temperature
To make a quick cooled beverages...
put it in ice water and salt goes before freezing point that cools beverage in less 5 minutes
Decreasing pressure __________ boiling temperature.
For every 1,000 feet elevation, boiling temperature decreases by about ?
Volumetric Expansion with Phase Change: liquid to vapor
water vapor has 1700 TIMES as compared to liquid water
Volumetric Expansion with Phase Change: solid to liquid
water expands when they heats up, when it costs it gets smaller, until about 4 C where it expands in order to form bonds
In hot beverages where does most of the environmental impact come from?
Milk, a milk in a cup creates more CO2 than boiling the water
Packaging of tea bags
loose tea has minimal packaging, nylon silk with envelope in cardboard box wrapped with plastic coating
What beverage provides the highest level of antioxidants?
Coffee (longer brew time = less antioxidants Darker Roast = more antioxidants)
Roasting Coffee Physics
CO2 goes out as it brews, diffusion, pour methods are better than machines
130F/54C, a method to cook food at relatively low temperature in circulating water for a long period of time, the water temperature is chosen to match the final temperature of the food, so as the temperature difference between the water and the food approach zero, the heat transfer rate also drops to zero, keep the water swirling, energy efficient
Slow Cook/ Passive Cook
180F/80C, slows the heat loss due to conduction to hold a safe cooking temperature for hours with no additional heat input
Boil & Simmer
212 F/100 C, beginning of quiver(140F), sub-simmer (140-195 F), full simmer (195-212f), Full Rolling Boil (212 F), most cooking is fine with a simmer and you save energy is much more efficient, avoiding a "rapid boil" saves energy
What's the most efficient way to boil water?
Microwave is least efficient, an electric kettle is the most efficient way
212 F/100 C, steaming only requires about an inch of water to steam, steaming requires the energy of vaporization
save time and energy, pressure change the environment in which the water boils, there form allowing for higher temperatures, used for different altitudes
As altitude goes up, does the boiling point temperature of water go up or down?
The boiling point of water decreases because atmospheric pressure decreases
Say you have two identical pans and one is maintained at 300°F and the other at 400°F. Now, if you add 0.5 oz of water to each, in which pan will the water evaporate quicker?
Water on the 300F pan NOT 400F
When you throw a handful of salt into a large pot of nearly boiling water, it will suddenly and rapidly come to a full rolling boil. Why?
Because you have provided nucleation sites for the vapor bubbles
In the Cook's Illustrated article: "The Science of Coffee Roasting" the author talks about the reactions that gives the coffee its distinctive flavor. We have studied these reactions earlier in the semester. They both occur above the 212 F boiling point of water. They are each used in this sentence: "While the Maillard reaction happens between sugars and amino acids, ____________ involves sugar alone."
While roasting coffee beans, there are two "cracks". What causes the FIRST crack?
steam escapes as beans fracture
In the article: "Brewing a great cup of coffee depends on chemistry and physics", it states: "There are three subtleties that have tremendous impact on the coffee quality". Which of these are NOT listed?
NOT How darkly roasted the bean
particle size distribution produced by the grinder
In "The Best (and Healthiest) Cup of Coffee: Could It All Be in the Brewing Method?", it talks about the impacts of roast time (darkness of roasted bean) on several factors. In general, darker roasts contain ____ caffeine as compared to lighter roasts.
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