What is the pressure difference?

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Homework Help Overview

The discussion revolves around a question regarding the pressure difference between two gases in a static system, specifically focusing on the interpretation of pressure readings and the implications of a teacher's response to a student's reasoning.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the relationship between gas pressure and mercury levels in a manometer setup, questioning the validity of the teacher's assertion that one gas has a higher pressure than the other. Some participants present their reasoning based on hydrostatic principles, while others reflect on the social dynamics of challenging authority in an educational setting.

Discussion Status

The discussion is ongoing, with various perspectives being shared. Some participants express a desire for open dialogue with the teacher, while others caution against public challenges. There is a mix of support for questioning the teacher and concern for maintaining classroom harmony.

Contextual Notes

There is a noted tension between the student's understanding of the physics involved and the teacher's explanation, which has not been elaborated upon. The participants are navigating the complexities of classroom dynamics and the implications of questioning a teacher's authority.

Tomy World
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TL;DR Summary: Which gas has a higher pressure and why? School has provided answer which I disagree. Like to hear comment from others.

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Welcome to PF.

If the system is static, then gas A has the higher pressure as it pushes the mercury towards the other gas B.
What do you think?
 
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Baluncore said:
Welcome to PF.

If the system is static, then gas A has the higher pressure as it pushes the mercury towards the other gas B.
What do you think?
Yah. It's quite straight forward, right?

My answer is
PA + ρgH1 = PB + ρgH2
PA = PB + ρg(H2-H1)

Since H2>H1, therefore PA > PB.

But teacher wrote the other way round, saying that PB is higher without given more explanation. And students hesitate to challenge teacher... I'd encourage them to openly discuss with teacher ;)
 
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Tomy World said:
And students hesitate to challenge teacher... I'd encourage them to openly discuss with teacher ;)
When you think a teacher gets it wrong, if you want good marks, do NOT challenge the teacher in front of the class. Give a copy of your work to the teacher after the class. Either you or the teacher will be wrong, neither of you needs public embarrassment or loss of face.
 
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Baluncore said:
When you think a teacher gets it wrong, if you want good marks, do NOT challenge the teacher in front of the class. Give a copy of your work to the teacher after the class. Either you or the teacher will be wrong, neither of you needs public embarrassment or loss of face.
May be 'challenge' is a strong word. I don't mean that ;)
 
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Your teacher should be ashamed. Ask if the teacher is sure of the result?
 
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With an error this egregious and a resolution that is relatively straightforward to work out, my inclination would be to challenge the teacher in class. The misunderstanding needs to be exposed, rather than swept under the carpet.

The one time I had a similar disagreement (I was correct, TA was in error), I wound up being disagreed with by the TA and berated by the rest of the class. I shut up so that we could get on with the rest of the subject matter. No big deal. I knew I was right. I knew the TA was wrong and I had a good idea why. I didn't need the grade or the peer approval. I was in school to learn, not to obtain a credential or to garner the respect of others.

At the beginning of our next session, the TA had the good grace to apologize in front of the class and provide the explanation of error that I had anticipated.
 
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jbriggs444 said:
With an error this egregious and a resolution that is relatively straightforward to work out, my inclination would be to challenge the teacher in class.
I agree. Any teacher who is offended by a POLITE challenge doesn't belong there.
 
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