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ryzh [129]
2 years ago
11

A refrigerator has a COP of 1.5. That is, the refrigerator removes 1.5 kWh of energy from the refrigerated space for each 1 kWh

of electricity it consumes. Is this a violation of the first law of thermodynamics? explain.
Engineering
1 answer:
svetoff [14.1K]2 years ago
3 0

Answer:

The answer is, It doesn't violate the first law of thermodynamics

Explanation:

The reason is that a refrigerator system does not create energy, it only does work by removing heat from a system or surrounding.

What is the first law of thermodynamics?

The first law of thermodynamics, also known as Law of Conservation of Energy, states that energy can neither be created nor destroyed; energy can only be transferred or changed from one form to another.

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A platinum resistance temperature sensor has a resistance of 120 Ω at 0℃ and forms one arm of a Wheatstone bridge. At this tempe
oksian1 [2.3K]

Answer : 9.36ohms/ temperature

Explanation:

Expression for the variation of resistance of platinum with temperature

Rt= Ro(1+*t)

Rt= resistance @ t°C

Ro= resistance @ 0°C

*= temperature coefficient of resistance

Calculate the change in resistance by putting 120ohms for Ro,

0.0039/K for *

20°C for t

Using this formula:

Rt = Ro(1+*t)

Rt- Ro = Ro*t

= (120ohms)(0.0039/K)(20°C)

= 9.36ohms/K

8 0
2 years ago
Develop a preliminary work breakdown structure (WBS) for a small one-story commercial building to be constructed on the site of
Zielflug [23.3K]

Answer:

The preliminary work breakdown structure will be divided into two steps, the first is to draw the first level and the second is to draw the second level.

Explanation:

Please look at attachment.

6 0
2 years ago
Read 2 more answers
All of these are true about GMA (MIG) welding EXCEPT that:
Hatshy [7]

Answer:

the welding gun liner regulates the shielding gas.

Explanation:

The purpose of the welding gun liner is to properly position the welding wire from the wire feeder till it gets to the nozzle or contact tip of the gun. <em>Regulation of the shielding gas depends on factors such as the speed, current, and type of gas being used. </em>In gas metal arc welding, an electric arc is used to generate heat which melts both the electrode and the workpiece or base metal.

The electric arc produced is shielded from contamination by the shielding gas. The heat generated by the short electric arc is low.

3 0
1 year ago
During an experiment conducted in a room at 25°C, a laboratory assistant measures that a refrigerator that draws 2 kW of power h
zvonat [6]

Answer:

Not reasonable.

Explanation:

To solve this problem it is necessary to take into account the concepts related to the performance of a reversible refrigerator. The coefficient of performance is basically defined as the ratio between the heating or cooling provided and the electricity consumed. The higher coefficients are equivalent to lower operating costs. The coefficient can be greater than 1, because it is a percentage of the output: losses, other than the thermal efficiency ratio: input energy. For a reversible refrigerator the coefficient is given by

COP_{R,rev} = \frac{1}{\frac{T_1}{T_2}-1}

Where,

T_1 =High temperature

T_2 =Low Temperature

With our values previous given we can find it:

T_2 = -30\°C = (-30+273)

T_2 = 243K

T_1 = 25\°C = (25+273)

T_1 = 298K

With these values we can now calculate the coefficient of performance:

COP_{R,rev} = \frac{1}{\frac{298}{243}-1}

COP_{R,rev} = 4.42

At the same time we can calculate the work consumption of the refrigerator, this is

W = \dot{W}\Delta t

Where,

\dot{W} = Required power input

t = time to remove heat from a cool to water medium

W = 2kJ/s * 20 min

W = 2kJ/s * 1200s

W = 2400kJ

In this way we can calculate the coefficient of the refrigerator directly:

COP_R = \frac{Q_L}{W}

Where,

Q = Amoun of heat rejected

COP_R = \frac{30000}{2400}

COP_R = 12.5

Comparing the values of both coefficients we have that the experiments are NOT reasonable, because the coefficient of a refrigerator is high compared to  coefficient of reversible refrigerator.

5 0
2 years ago
Given the following code, what indexes must be passed to the substring method to produce the new String with the value "SCORE"?
Ierofanga [76]

Answer:

For expr1 = index 5, length 5

For expr2 = index 0, length 4 and index 21, length 5

string quote = "Four score and seven years ago";

           string expr1 = quote.Substring(5, 5).ToUpper(); // "SCORE"  

           string expr2 = quote.Substring(0, 4) + quote.Substring(21, 5).ToLower(); // "fouryears"

           Console.WriteLine(expr1);

           Console.WriteLine(expr2);

Explanation:

Then code is written in c# and it produces SCORE and f

ouryears

Substring takes 2 arguments, the start of the specific character and the length

6 0
2 years ago
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