# Thermal physics problem -- Pressure and temperature of air in a refrigerator

• ib43
In summary, the conversation discusses a problem involving a refrigerator in a kitchen. The first part calculates the number of air molecules in the refrigerator when its door is open, while the second part determines the pressure inside the refrigerator with its closed door and calculates the minimum force needed to open the door. The solution involves using the ideal gas law and considering the pressure difference between inside and outside the refrigerator.
ib43
Homework Statement
I am stuck on one particular section regarding finding force given pressure
Relevant Equations
pv=nRT, P=F/A
There is this one problem from past exam papers which I cannot seem to do:

The air in a kitchen has pressure 1.0 x 10^5 Pa and temperature 22'C. A refrigerator of internal volume 0.36 m^3 is installed in the kitchen.

(a) With the door open the air in the refrigerator is initially at the same temperature and pressure as the air in the kitchen. Calculate the number of molecules of air in the refrigerator.

(b) The refrigerator door is closed. The air in the refrigerator is cooled to 5.0'C and the number of air molecules in the refrigerator stays the same.

(i) Determine the pressure of the air inside the refrigerator.

(ii) The door of the refrigerator has an area of 0.72m^2. Show that the minimum force needed to open the refrigerator door is about 4 kN

My attempts:

a) I simply used the equation pV=NKT where p = 1.0 x 10^5 and T=295, and K = Boltzmann constant, V=0.36. This gave me the number of molecules.
b) i) I used P1/T1=P2/T2 where I am trying to find P2, where P1, T1, are given and T2= 278.
ii) I assumed we can use the pressure found in part b i) then use P=F/A but it does not seem to give me the answer of 4kN.

Last edited:
Why use the pressure from part bi? What is keeping the door shut?

Find the pressure inside using what you got in part B times the area. Then find the pressure outside which is the given pressure times the same area. So, to find the minimum force to open it, you find the difference. So with sig figs taken into consideration, I got 72,000(force outside) - 68,000(force inside) = 4 kN.

## What is the relationship between pressure and temperature in a refrigerator?

The pressure and temperature of air in a refrigerator are directly related to each other. As the temperature decreases, the pressure also decreases. This is due to the ideal gas law, which states that the pressure of a gas is inversely proportional to its temperature.

## Why is it important to maintain a specific pressure and temperature in a refrigerator?

Maintaining a specific pressure and temperature in a refrigerator is important for several reasons. First, it ensures that the food inside stays fresh and safe to eat. Second, it helps the refrigerator run efficiently and saves energy. Finally, it prevents any damage to the refrigerator's components.

## How does a refrigerator maintain a specific pressure and temperature?

A refrigerator uses a refrigerant, such as Freon, to absorb heat from the inside and release it outside. As the refrigerant evaporates, it cools the air inside the refrigerator, lowering the temperature. The compressor then compresses the refrigerant, increasing its pressure and temperature. The refrigerant then condenses and releases the heat outside, maintaining a specific pressure and temperature inside the refrigerator.

## What factors can affect the pressure and temperature in a refrigerator?

Several factors can affect the pressure and temperature in a refrigerator. These include the type and amount of refrigerant, the efficiency of the compressor, the ambient temperature, and the amount of food and items inside the refrigerator.

## How can I troubleshoot pressure and temperature issues in my refrigerator?

If you notice that your refrigerator is not maintaining a specific pressure and temperature, there may be an issue with the refrigerant, compressor, or other components. It is best to consult a professional for troubleshooting and repairs to ensure the safety and efficiency of your refrigerator.

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