1answer.
Ask question
Login Signup
Ask question
All categories
  • English
  • Mathematics
  • Social Studies
  • Business
  • History
  • Health
  • Geography
  • Biology
  • Physics
  • Chemistry
  • Computers and Technology
  • Arts
  • World Languages
  • Spanish
  • French
  • German
  • Advanced Placement (AP)
  • SAT
  • Medicine
  • Law
  • Engineering
babymother [125]
3 years ago
13

A microwave oven operates on the principle that application of a high-frequency field causes electrically polarized molecules su

ch as water within the food to oscillate. Rapid alignment and reversal of water molecules results in a nearly uniform generation of thermal energy within the food and, in turn, cooking of the food. When the food is initially frozen, however, the water molecules do not readily oscillate in response to the microwaves, and the volumetric heat generation rates are between one and two orders of magnitude lower than if the water were in liquid form. Microwave power that is not absorbed in the food is reflected back to the microwave generator, where it is dissipated in the form of heat to prevent damage to the generator.
a. Consider a frozen, 1-kg spherical piece of ground beef at an initial temperature of -20 degrees C placed in a microwave oven with total power of 1 kW, air temperature of 30 degrees C, and heat transfer coefficient of 15 W/m^2*K. Assuming the temperature within the beef to be uniform, determine how long it would take the beef to reach a temperature of 0 degrees C, with all the water in the form of ice and 3% of the oven power absorbed by the food. You may assume the physical properties of the beef to be the same as those of ice (p = 920 kg/m^3; c = 2,000 J/kg*K; k = 2.2 W/m*K) in this case.

b. After all the ice is converted to liquid, determine how long it would take to heat the beef to a uniform temperature of 80 degrees C if the temperature within the beef is still assumed to be uniform and 95% of the oven power is absorbed in the food. Assume the properties of the beef are now the same as those of liquid water (p = 1,000 kg/m^3; c = 4,200 J/kg*K; k = 0.6 W/m*K).

c. When thawing food in microwave ovens, you may observe that part of the food is still frozen while other parts of the food are overcooked. Can you explain why this occurs? Explain why most microwave ovens have thaw cycles with very low oven power

Physics
1 answer:
Tema [17]3 years ago
6 0

Answer:

a

The time it would take the beef to reach a temperature of 0⁰C is t= 662 sec = 11.93 min

b)

The time it would take to heat the beef to uniform temperature of 80⁰C is

t = 365 sec =5.93 min

c

 Efficient absorption of Microwave power is in regions of liquid water . Hence if the food or the microwave irradiation  is not uniform, the power will be absorbed non-uniformly, resulting in a non-uniform temperature rise. Defrost region will absorb more energy per unit volume than frozen region.if food is of low thermal conductivity, there will be insufficient time for heat conduction to make the temperature more uniform.Use of low power allows more time for conduction to occur.  

Explanation:

The explanation is shown on the first second and third uploaded image

You might be interested in
Does the orbital period of a planet depend on the mass of the planet or on the mass of the star that it orbits?
jasenka [17]

Answer:

The orbital period of a planet depends on the mass of the planet.

Explanation:

A less massive planet will take longer to complete one period than a more massive planet.

8 0
2 years ago
A physics student tests the theory of projectile motion by leaping off a 225 meter tall building. She runs off the building hori
tamaranim1 [39]
In this item, we are given with the x-component of the velocity. The y-component is equal to 0 m/s. The time it takes for it to reach the volume can be related through the equation,

   d = V₀t + 0.5gt²

Substituting the known values,

  225 = (0 m/s)(t) + (0.5)(9.8)(t²)

Simplifying,
 
   t = 6.776 s

To determine the distance of the student from the edge of the building, we multiply the x-component by the calculated time.


   range = (12.5 m/s)(6.776 s)

   range = 84.7 m

<em>Answer: 84.7 m</em>

4 0
3 years ago
On a sunny day, a student poured a cup of water on the sidewalk to make a puddle. When he returned later, the puddle was gone. T
ivanzaharov [21]

Answer:

The students conclusion is wrong.

Explanation:

The students conclusion is wrong because liquids can not soak into concrete. The water evaporated because it was a hot sunny day. The water turned into a gas called water vapor.

8 0
3 years ago
3. Provide two examples of static electric charge.
Rzqust [24]

Answer: 1.  walking across a carpet and touching a metal door handle            2. pulling your hat off and having your hair stand on end.

Explanation

:)

5 0
3 years ago
Give an example of a situation in which you would describe an
Viktor [21]
It would be A because it would make sense
5 0
3 years ago
Other questions:
  • The branch of science concerning heat flow and energy conversions is called _____. chemistry thermodynamics conversion science a
    13·2 answers
  • The distance from the earth to a star that has identical apparent and absolute magnitudes is ____ .
    10·1 answer
  • A coefficient in a chemical formula shows the number of electrons?<br><br> True<br> False
    15·2 answers
  • An apple weighs 1.00 N. When you hang it from the end of a long spring of force constant 1.50 N/m and negligible mass, it bounce
    6·1 answer
  • Problem:
    10·1 answer
  • How many times more gravitational potential energy would the same lander have on top of a 350-m hill on Earth? It would have tim
    7·1 answer
  • 77. The first law of motion applies to
    8·1 answer
  • There is a small hole of radius r in a hollow sphere, which is immersed in a liquid. Upto what maximum depth it can be immersed
    9·1 answer
  • Calculate the following
    8·1 answer
  • what is q if 28.6 g of water is heated from 22.0°c to 78.3°c? the specific heat of water is 4.184 j/g·°c.
    5·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!