Pressure in Liquids

  • #1

Homework Statement


upload_2018-4-16_18-13-3.png


Homework Equations


How does atmospheric pressure affects the volume of liquid? What will be the volume of the air bubble at the bottom of the lake?

The Attempt at a Solution


At the surface, the volume is 6.0cm3. So at the bottom, more pressure will be exerted so it will be halved to 3cm3. Please explain the concept, that was just a rough idea.

Thanks.
(regards)
 

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Answers and Replies

  • #2
TSny
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The problem says, "Water of depth 10 m exerts a pressure equal to atmospheric pressure". Is this pressure an absolute pressure or a gauge pressure? In other words, if you had a lake that is 10 m deep, what would be the gauge pressure at the bottom of the lake? What would be the absolute pressure at the bottom?
 
  • #3
The problem says, "Water of depth 10 m exerts a pressure equal to atmospheric pressure". Is this pressure an absolute pressure or a gauge pressure? In other words, if you had a lake that is 10 m deep, what would be the gauge pressure at the bottom of the lake? What would be the absolute pressure at the bottom?
I am not familiar with the terms ''Gauge Pressure'' and ''Absolute Pressure''. Can you make it more simple..
 
  • #4
TSny
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Gauge pressure is pressure measured relative to atmospheric pressure. Many pressure gauges measure gauge pressure (such as a gauge for measuring pressure in a tire). Absolute pressure is the "true" or "actual" pressure. A gauge pressure of 0 corresponds to an absolute pressure of 1 atmosphere. A gauge pressure of 0.5 atmospheres corresponds to an absolute pressure of 1.5 atmospheres.

The important thing in this problem is to know what the absolute pressure is at the top of the lake and also at the bottom of the lake.

If the lake is 20 m deep, what is the (absolute) pressure at the top of the lake? What is the (absolute) pressure at the bottom of the lake?
 
  • #5
Gauge pressure is pressure measured relative to atmospheric pressure. Many pressure gauges measure gauge pressure (such as a gauge for measuring pressure in a tire). Absolute pressure is the "true" or "actual" pressure. A gauge pressure of 0 corresponds to an absolute pressure of 1 atmosphere. A gauge pressure of 0.5 atmospheres corresponds to an absolute pressure of 1.5 atmospheres.

The important thing in this problem is to know what the absolute pressure is at the top of the lake and also at the bottom of the lake.

If the lake is 20 m deep, what is the (absolute) pressure at the top of the lake? What is the (absolute) pressure at the bottom of the lake?
Sorry, I do not understand..
 
  • #6
TSny
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Forget the concept of gauge pressure. I didn't know that you are not familiar with it. It is not necessary for this problem.

You have to interpret carefully the meaning of the statement "Water at a depth of 10 m exerts a pressure of 1 atmosphere". This means that for every 10 m deeper that you go down in water, the pressure increases by 1 atmosphere.

If we have a lake of depth 20 m, can you answer the following?

(1) What is the pressure at the top of the lake?
(2) What is the pressure at a depth of 10 m in the lake?
(3) What is the pressure at a depth of 20 m (at the bottom of the lake)?
 
  • #7
Forget the concept of gauge pressure. I didn't know that you are not familiar with it. It is not necessary for this problem.

You have to interpret carefully the meaning of the statement "Water at a depth of 10 m exerts a pressure of 1 atmosphere". This means that for every 10 m deeper that you go down in water, the pressure increases by 1 atmosphere.

If we have a lake of depth 20 m, can you answer the following?

(1) What is the pressure at the top of the lake?
(2) What is the pressure at a depth of 10 m in the lake?
(3) What is the pressure at a depth of 20 m (at the bottom of the lake)?
1) 0 atmosphere
2) 1 atmosphere
3) 2 atmospheres
Am I right?
 
  • #8
TSny
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1) 0 atmosphere
2) 1 atmosphere
3) 2 atmospheres
Am I right?
No. You have forgotten that the surface of the lake is exposed to the atmosphere. So, the pressure at the surface is not 0.
 
  • #9
No. You have forgotten that the surface of the lake is exposed to the atmosphere. So, the pressure at the surface is not 0.
It should be 1 too?
 
  • #10
TSny
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It should be 1 too?
Right. So, what are the answers to the three questions of post #8?
 
  • #11
Right. So, what are the answers to the three questions of post #8?
1) 1 atmosphere
2) 2 atmospheres
3) 3 atmospheres
 
  • #12
TSny
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  • #14
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Have you studied the ideal gas law?
 
  • #15
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use Boyle's law : P1V1 = P2V2
 
  • #17
TSny
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I have studied P1V1 = P2V2
OK. That's a special case of the ideal gas law when the temperatures in states 1 and 2 are the same. The equation P1V1 = P2V2 is called "Boyle's law" as mentioned by @patric44

Can you use Boyle's law to get the answer?
 
  • #18
OK. That's a special case of the ideal gas law when the temperatures in states 1 and 2 are the same. The equation P1V1 = P2V2 is called "Boyle's law" as mentioned by @patric44
By using the Boyle's Law, the answer is 2 cm3. Is it correct?
 
  • #19
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  • #21

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