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Homework Help: Ray diagram

  1. May 9, 2016 #1
    Fairly simple question I'd like someone to help with please. My teacher has me confused so I figured I'd turn to the forums for help.

    1. Alright, so in an exam we had a ray diagram to draw. "Complete the ray diagram shown in Figure 6" they said (I sketched a replica * thumbs up* hongjinyoungreferenceimsorry):

    Alrighty. (No relevant equations so I'm jumping to step three)

    3. I attempted it because, you know, it was an exam. I drew these emerging rays in yellow:


    However, after the exam, I realized I drew it wrong? The lens seemed to be a diverging one so I sulked thinking that I'd get it wrong. I reattempted all the questions in the exam at home and I drew this for this particular question:
    Since the lens seems to be divergent, the rays should diverge, no?

    But no! I received my exam paper and my teacher marked the exam ray diagram correct and gave me the two marks that came with it.

    So I'd really appreciate it if someone would deliver me from this time of confusion. Does that really represent a diverging lens so the third picture is correct? Or is it a converging lens so that the second picture is correct?
    Thanks in advance!
  2. jcsd
  3. May 9, 2016 #2
    I find it strange the symbols for the various lenses were not introduced before the exam. Did other students complain?
  4. May 10, 2016 #3
    Its not that strange, honestly, it's just how it is. You see, my teacher rarely ever attends classes and when he does, he reaches sometimes twenty minutes before the bell rings and simply lectures us on life goals, the expectations of us, and talks about the country's state. He hardly teaches. It's up to us to either go to paid classes outside school or dive into our textbooks and learn everything there. We've complained so many times but they haven't done anything about it. We asked other teachers about it and they said that he does this to every class, every year. It's unfair.

    I learn from my textbook. They mainly focused on converging lenses and showed us ray diagrams for them.
  5. May 10, 2016 #4
    They drew the converging lenses like a ellipse-diamond mutant.
  6. May 10, 2016 #5
    I do not think that this is the place to post opinions of teachers.
    The answers and explanations to physics questions have nothing to do with the competence of teachers either here or elsewhere.
    Text books are a good source of exlanation.
  7. May 10, 2016 #6


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    Yes. Your exam answer should have been marked wrong.
  8. May 10, 2016 #7
  9. May 10, 2016 #8
    "mfig" asked so I answered. But thanks, I'll keep you advice in mind for future threads. :ok:
    And yeah, textbooks are great sources for explanations.
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