SOURCES OF ENERGY AND HEAT TRANSFER

Question 1

What is conduction?

Answer 1

The direct transfer of energy from one solid body to another. Vibrating molecules from one surface will strike the relatively still molecules of another, thereby transferring energy.

Question 2

By far the most efficient method of heat transfer.

Answer 2

Conduction

Question 3

Examples of heat transfer through conduction.

Answer 3

Searing a steak
Crisping the bottom of pizza
Cooking scrambled eggs
Making grill marks on a burger
Sautéing onions

Question 4

What is convection?

Answer 4

The transfer of one solid body to another through the intermediary of a fluid–that is, liquid or gas.

Question 5

Is convection efficient?

Answer 5

Moderately, though in cooking its efficiency depends greatly on the way the fluid flows around the food.

Question 6

The motion of fluid if referred to as what?

Answer 6

Convection patterns.

Question 7

What is the general rule about air speed flowing over a given surface? Explain.

Answer 7

The faster it flows, the more energy it can transfer. Still air will rapidly give up its energy, but with moving air, the energy supply is constantly being replenished by new air being cycled over a substance such as food.

Question 8

What are convection oven fans designed for?

Answer 8

To keep air moving around at a good clip to promote faster, more even cooking.

Question 9

Will agitating oil when deep frying lead to foods that crisp and brown more efficiently?

Answer 9

Yes

Question 10

Examples of heat transfer through convection.

Answer 10

Steamed asparagus
Boiling dumplings in stock
Deep-frying onion rings
BBQing a pork shoulder
The top of a pizza baking in an oven

Question 11

What is radiation?

Answer 11

Transfer of energy through space via electromagnetic waves.

Question 12

Does radiation require a medium to transfer?

Answer 12

No

Question 13

An important fact to remember about radiant energy.

Answer 13

It decays.

Question 14

Why does radiant energy decay (get weaker)?

Answer 14

By the inverse square law–the energy that reaches an object from a radiant energy source is proportional to the inverse of the square of its distance.

Question 15

Example of radiant energy decaying.

Answer 15

Hold your hand 1 foot away from the fire, then move it two feet away. Even though you’ve doubled your distance, the fire will feel only about one-quarter as hot.

Question 16

Examples of radiant heat transfer.

Answer 16

Roasting a pig on a spit next to hot coals
Toasting garlic bread under the broiler
Getting tan from the sun
Broiling some marinated salmon

Question 17

Most of the time, in cooking, are all three methods of heat transfer used? Example.

Answer 17

Yes, to varying extents. Burger on the grill uses radiant heat (fire), convection (lid) and conduction (grill grate).

Question 18

The only other standard method of energy transfer we commonly use in the kitchen.

Answer 18

Microwaves

Question 19

Microwaves have the unique ability to what?

Answer 19

Penetrate through the exterior of food when heating it.

Question 20

Just like heat, microwaves are a form of what?

Answer 20

Electromagnetic radiation.

Question 21

When microwaves are aimed at an object with magnetically charged particles, those particles do what?

Answer 21

Rapidly flip back and forth, creating friction.

Question 22

Microwaves can pass through most solid objects to a depth of what?

Answer 22

At least a few centimeters or so; not a relatively slow transfer of energy - better than the conduction, convection, radiation.

Question 23

Most people can hold there hand in a 200ºF oven for how long?

Answer 23

30 seconds or so.

Question 24

Water over what temp generally becomes painful to the touch?

Answer 24

135ºF

Question 25

Water at what temp is hot enough to scald you?

Answer 25

180ºF

Question 26

Water at what temp will blister and scar you?

Answer 26

212ºF

Question 27

How does a lower temperature of water burn you while a higher temperature oven will simply be uncomfortable?

Answer 27

There are many more molecules in a cup of water than in air. Therefore, the water has more energy and heats up your hand much more rapidly.

Question 28

Does food cook faster in a dry or moist oven? Why?

Answer 28

A moist oven has denser air and more energy, cooking the food faster.

Question 29

Will boiled foods cook faster than baked or roasted food?

Answer 29

Yes