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
Which of the following is not true? A) The energy of the sun comes from nuclear fusion. B) The fuel for nuclear fusion comes fr
denpristay [2]

Answer:

Option B) The fuel for nuclear fusion comes from sea water

Explanation:

Nuclear fusion can not be carried out by using any type of water as water is composed of stable water molecules (H_{2}O which is quite difficult to be decayed by any simple method.

Moreover, fusion reactions demands the combination of nuclei of lighter elements for which it makes use of the heavy isotopes of Hydrogen that are Deuterium and Tritium as fuel to carry out the nuclear fusion.

4 0
2 years ago
(a) If two sound waves, one in a gas medium and one in a liquid medium, are equal in intensity, what is the ratio of the pressur
GarryVolchara [31]

Answer:

(a) The ratio of the pressure amplitude of the waves is 43.21

(b) The ratio of the intensities of the waves is 0.000535

Explanation:

Given;

density of gas, \rho _g = 2.27 kg/m³

density of liquid, \rho _l = 972 kg/m³

speed of sound in gas, C_g = 376 m/s

speed of sound in liquid, C_l = 1640 m/s

The of the sound wave is given by;

I = \frac{P_o^2}{2 \rho C} \\\\P_o^2 = 2 \rho C I\\\\p_o = \sqrt{2 \rho CI}

Where;

P_o is the pressure amplitude

P_o_g= \sqrt{2 \rho _g C_gI} -------(1)\\\\P_o_l= \sqrt{2 \rho _l C_lI}---------(2)\\\\\frac{P_o_l}{P_o_g} = \frac{\sqrt{2 \rho _l C_lI}}{\sqrt{2 \rho _g C_gI}} \\\\\frac{P_o_l}{P_o_g} = \sqrt{\frac{2 \rho _l C_lI}{2 \rho _g C_gI} }\\\\ \frac{P_o_l}{P_o_g} = \sqrt{\frac{ \rho _l C_l}{ \rho _g C_g} }\\\\ \frac{P_o_l}{P_o_g} = \sqrt{\frac{ (972)( 1640)}{ (2.27)( 376)} }\\\\\frac{P_o_l}{P_o_g} = 43.21

(b) when the pressure amplitudes are equal, the ratio of the intensities is given as;

I = \frac{P_o^2}{2 \rho C}\\\\I_g = \frac{P_o^2}{2 \rho _g C_g}-------(1)\\\\I_l = \frac{P_o^2}{2 \rho _l C_l}-------(2)\\\\\frac{I_l}{I_g} = (\frac{P_o^2}{2 \rho _l C_l})*(\frac{2\rho_gC_g}{P_o^2} )\\\\\frac{I_l}{I_g} = \frac{\rho _gC_g}{\rho_lC_l} \\\\\frac{I_l}{I_g} = \frac{(2.27)(376)}{(972)(1640)}\\\\ \frac{I_l}{I_g} = 0.000535

3 0
3 years ago
Could You Take 2 Elements From The Periodic Table Of Elements, and possibly make one of other 116 elements that are on the table
LekaFEV [45]
That's what stars do all the time. 
For example, in the sun (and MOST other stars), deep down in the center
of the sun's core, two atoms of Hydrogen get squashed together so hard
that they blend into one atom of Helium AND release some energy. 
That's where the sun's energy all comes from.  It's called "nuclear fusion". 
It needs tremendous temperature and pressure to happen.  We know how
to do it, but we can't control it.  So far, the only thing we've ever been able
to use it for is Hydrogen bombs.   

There are 92 elements on the Periodic Table that are found in nature,
plus another 20 or so that have been made in the laboratory, but only
a few atoms of them.
5 0
3 years ago
Read 2 more answers
When a scientist contrasts two or more objects what is he or she looking for?
tekilochka [14]
When your Contrasting multiple objects, your looking for any differences that may or may not be their. Think Compare and Contrast if that helps, The answer to this is A
5 0
2 years ago
Read 2 more answers
Which two particles would be attracted to each other?
rusak2 [61]
A. electrons<span> and </span>neutrons<span> B. </span>electrons<span> and </span>protons<span> C. </span>protons<span> and </span>neutrons<span> D. all particles are attracted to each other. According to atomic theory, </span>electrons<span> are usually found: A. in the </span>atomic nucleus<span> B. outside the nucleus, yet very near it because they are attracted to the </span>protons<span>.</span>
5 0
2 years ago
Other questions:
  • Went to make a sandwich<br> what ingredients do I need
    15·1 answer
  • Review Multiple-Concept Example 7 in this chapter as an aid in solving this problem. In a fast-pitch softball game the pitcher i
    15·1 answer
  • The tip of a pinwheel is 0.24 m from the center. The pinwheel spins 5 times each second. What is the tangential speed of the tip
    5·2 answers
  • A steam catapult launches a jet aircraft from the aircraft carrier john C. Stennis, giving it a peed of 175 mi/h in 2.50 . (a) F
    7·1 answer
  • In which kingdoms are all organisms multicellular
    6·1 answer
  • A sinusoidal electromagnetic wave is propagating in a vacuum in the +z-direction. If at a particular instant and at a certain po
    15·1 answer
  • • Be able to identify the forms of kinetic vs. potential energy, and to list some forms of each. • Be able to state the Law of C
    15·1 answer
  • rce versus time during the collision of a 44- tennis ball with a wall. The initial velocity of the ball is 36 perpendicular to t
    8·1 answer
  • Explain including specific heat in your response, why the average Long Island ocean water temperature in May (52F) is cooler tha
    8·2 answers
  • Many firms develop a formal _____ to answer the question: who is your target market and how do you plan to reach them?
    6·1 answer
Add answer
Login
Not registered? Fast signup
Signup
Login Signup
Ask question!