What is the pressure difference?

[Tomy World]

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

 

[Baluncore]

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?

 

[Tomy World]

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 ;)

 

[Baluncore]

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.

 

[Tomy World]

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 ;)

 

[Chestermiller]

Your teacher should be ashamed. Ask if the teacher is sure of the result?

 

[jbriggs444]

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.

 

[Herman Trivilino]

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.