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**Physics...Before/After**

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    #272
    Bears and Vodka
    Registered Users Posts: 2,249 ✭✭✭Bears and Vodka


    mathstalk wrote: »
    Where exactly in the tables is the charge of the proton? I couldn't find it anywhere. I think I might have had the old tables. It wasn't even on the page telling us the masses of the electron etc.

    Electon has a charge of -1. Proton has a charge of +1. So I think you have to go by the assumption that the charge of proton is the same as charge of the electron and it's 1.6x10^-19 C.


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    #273
    Cathalog
    Registered Users Posts: 329 ✭✭Cathalog


    mathstalk wrote: »
    Cathalog wrote: »
    Rainbow:
    Rain
    Sun
    Something else

    Q8: you didn't use enough significant figures :( It was close to 0. You were supposed to use the log tables to find the charge on the proton.

    Where exactly in the tables is the charge of the proton? I couldn't find it anywhere. I think I might have had the old tables. It wasn't even on the page telling us the masses of the electron etc.

    Same as the charge on an electron.


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    #274
    Chuchoter
    Registered Users Posts: 4,306 ✭✭✭Chuchoter


    That was a nice enough paper! Tough modern physics question, took about 10 years to do all the table flicking!


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    #275
    Liveforrugby
    Registered Users Posts: 343 ✭✭Liveforrugby


    finality wrote: »
    I think it's equal to the charge on the electron isn't it?

    Am i missing something here... charge on a proton is +1 charge on an electron is -1? Am I over simplfying something?


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    #276
    Tankosaur
    Registered Users Posts: 102 ✭✭Tankosaur


    Liveforrugby wrote: »
    Am i missing something here... charge on a proton is +1 charge on an electron is -1? Am I over simplfying something?

    They have the same quantity of charge just opposite values of that charge.


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    #277
    mathstalk
    Registered Users Posts: 162 ✭✭mathstalk


    subz3r0 wrote: »
    You draw the normal line on the thing to help you. In either case, the symbol theta was drawn on the angle they want you to find.

    I know that but what side of the block are they talking about when they say parallel? Parallel to this side:

    z3WqD.png

    Or to this side:

    NHife.png


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    #278
    mcpaddington
    Closed Accounts Posts: 358 ✭✭mcpaddington


    Just looking for a confirmation on question 1. So were we supposed to draw the line on the test itself?


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    #279
    mathstalk
    Registered Users Posts: 162 ✭✭mathstalk


    Cathalog wrote: »
    Same as the charge on an electron.

    Ah that's what I used! Brilliant!
    mcpaddington wrote: »
    Just looking for a confirmation on question 1. So were we supposed to draw the line on the test itself?

    The question doesn't specify. It's badly phrased. Don't worry, you'll get marks for what you did.


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    #280
    Bears and Vodka
    Registered Users Posts: 2,249 ✭✭✭Bears and Vodka


    A few questions about Question 5.

    a) Cork and Sligo. Did ye get 288.75 km?

    g) Person smokes bla bla bla. Is the answer convection currents in the air and draught bringing the smoke into the building?


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    #281
    Liveforrugby
    Registered Users Posts: 343 ✭✭Liveforrugby


    I better leave before I find out I made even more mistakes..


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    #282
    Epsi
    Registered Users Posts: 58 ✭✭Epsi


    mathstalk wrote: »
    Where exactly in the tables is the charge of the proton? I couldn't find it anywhere. I think I might have had the old tables. It wasn't even on the page telling us the masses of the electron etc.

    This annoyed me as well. Didn't know the value for it and had about 1 minute left at the end , So wrote down the opposite charge of the Electron (I know this is incorrect) plugged it all in and got a ridiculous answer. Thought I'd make a stab at it with barely any time left.

    Same as the charge on an electron.

    Thank heavens , So I wasn't crazy.


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    #283
    mcpaddington
    Closed Accounts Posts: 358 ✭✭mcpaddington


    subz3r0 wrote: »
    A few questions about Question 5.

    a) Cork and Sligo. Did ye get 288.75 km?

    g) Person smokes bla bla bla. Is the answer convection currents in the air and draught bringing the smoke into the building?

    That's what I got anyway.


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    #284
    Tankosaur
    Registered Users Posts: 102 ✭✭Tankosaur


    May I ask what people answered for the question on diffraction of x-rays? I said that they will be diffracted but not to the same extent as light as their wavelenghts are very different.

    Also I did every question on the paper..... am I the only one?


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    #285
    Bears and Vodka
    Registered Users Posts: 2,249 ✭✭✭Bears and Vodka


    mathstalk wrote: »
    I know that but what side of the block are they talking about when they say parallel? Parallel to this side:

    z3WqD.png

    Or to this side:

    NHife.png

    Ah I getcha. I also contemplated putting down 90 degrees for angle theta.
    But if you look at it they want the critical angle of the block in the question.

    I think the marking scheme will allow both answers.


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    #286
    finality
    Registered Users Posts: 1,763 ✭✭✭finality


    Liveforrugby wrote: »
    Am i missing something here... charge on a proton is +1 charge on an electron is -1? Am I over simplfying something?

    Yes. That's in terms of the charge on the electron. like charge on electron is -1(1.6x10^-19) so proton is the same as that but positive


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    #287
    Bears and Vodka
    Registered Users Posts: 2,249 ✭✭✭Bears and Vodka


    mathstalk wrote: »
    The question doesn't specify. It's badly phrased. Don't worry, you'll get marks for what you did.

    Yes it does.
    Draw the appropriate graph on this examination paper.

    You draw the line of best fit on the thing itself, shove it in your booklet and voila.


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    #288
    Tankosaur
    Registered Users Posts: 102 ✭✭Tankosaur


    subz3r0 wrote: »
    A few questions about Question 5.

    a) Cork and Sligo. Did ye get 288.75 km?

    g) Person smokes bla bla bla. Is the answer convection currents in the air and draught bringing the smoke into the building?

    Yea I got that value of distance but you had to say north as it asked for displacement.

    For the smoke I said the smoke is warm so it is lens dense and therefore it rises above the cold air through the building. Strange question I thought.


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    #289
    finality
    Registered Users Posts: 1,763 ✭✭✭finality


    subz3r0 wrote: »
    A few questions about Question 5.

    a) Cork and Sligo. Did ye get 288.75 km?

    g) Person smokes bla bla bla. Is the answer convection currents in the air and draught bringing the smoke into the building?

    I also said that the smoke would diffuse out to cover a large area


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    #290
    mathstalk
    Registered Users Posts: 162 ✭✭mathstalk


    subz3r0 wrote: »
    Ah I getcha. I also contemplated putting down 90 degrees for angle theta.
    But if you look at it they want the critical angle of the block in the question.

    I think the marking scheme will allow both answers.

    I guessed that's what they wanted too, but it's annoying when they try to make it sound cryptic and end up making communicative errors in the process.


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    #291
    Tankosaur
    Registered Users Posts: 102 ✭✭Tankosaur


    mathstalk wrote: »
    Ah that's what I used! Brilliant!



    The question doesn't specify. It's badly phrased. Don't worry, you'll get marks for what you did.


    It said to draw your own graph

    Edit: it did not apparently...

    I did it anyway. My value of g was 9.86 so it doesn't matter really.


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    #292
    c28omzk7ihsxv0
    Closed Accounts Posts: 878 ✭✭✭c28omzk7ihsxv0


    That could have gone worse....

    It cold have gone better too...


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    #293
    iLaura
    Registered Users Posts: 619 ✭✭✭iLaura


    Tankosaur wrote: »
    May I ask what people answered for the question on diffraction of x-rays? I said that they will be diffracted but not to the same extent as light as their wavelenghts are very different.

    Also I did every question on the paper..... am I the only one?

    I asked my teacher about the x-ray one. Supposedly x-rays won't be diffracted as their wavelength is too short, or something like that :P
    mcpaddington wrote: »
    Just looking for a confirmation on question 1. So were we supposed to draw the line on the test itself?

    As I said a couple of posts back, it was a mistake on behalf of the SEC, and you get the full 15 marks for just finding the acceleration.


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    #294
    Bears and Vodka
    Registered Users Posts: 2,249 ✭✭✭Bears and Vodka


    Tankosaur wrote: »
    It said to draw your own graph

    It clearly didn't .. ?


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    #295
    Epsi
    Registered Users Posts: 58 ✭✭Epsi


    Tankosaur wrote: »
    Yea I got that value of distance but you had to say north as it asked for displacement.

    For the smoke I said the smoke is warm so it is lens dense and therefore it rises above the cold air through the building. Strange question I thought.

    I said the smoke would diffuse into the build , then gave the definition of diffusion. I remember that definition from biology though , and couldn't remember if it was a definition on the physics course.


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    #296
    mathstalk
    Registered Users Posts: 162 ✭✭mathstalk


    finality wrote: »
    I also said that the smoke would diffuse out to cover a large area

    I said the air pressure inside the building is smaller than outside, so the smoke, along with air, would get "sucked" into the building. Both answers seem correct, but sadly from my observation of past marking schemes, they'll probably only accept one. Which one? Who knows.
    iLaura wrote: »
    I asked my teacher about the x-ray one. Supposedly x-rays won't be diffracted as their wavelength is too short, or something like that

    I said that they would get diffracted, but to a lesser extent.


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    #297
    Tankosaur
    Registered Users Posts: 102 ✭✭Tankosaur


    subz3r0 wrote: »
    It clearly didn't .. ?


    I know, I was wrong. I edited it instantly, I misread what they were on about.


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    #298
    Tankosaur
    Registered Users Posts: 102 ✭✭Tankosaur


    iLaura wrote: »
    I asked my teacher about the x-ray one. Supposedly x-rays won't be diffracted as their wavelength is too short, or something like that :P

    It will be diffracted but very, very little.

    Light can be diffracted by a grating, x rays are diffracted by the distance between atoms in graphite crystal structures.


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    #299
    ECM2012
    Registered Users Posts: 10 ✭ECM2012


    In the nuclear physics question, if you multiplied the mass of an electron by the mass numbers of 3H and 2H without using the values in the log tables, would you say that's ok? I was going to use the values in the tables but they were the same but with loads of decimel places.. Didnt think it made a huge difference at the time but I'm doubting myself now


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    #300
    Tankosaur
    Registered Users Posts: 102 ✭✭Tankosaur


    mathstalk wrote: »
    I said the air pressure inside the building is smaller than outside, so the smoke, along with air, would get "sucked" into the building. Both answers seem correct, but sadly from my observation of past marking schemes, they'll probably only accept one. Which one? Who knows.



    I said that they would get diffracted, but to a lesser extent.

    Air pressure is the same everywhere at the same altitude, otherwise our ears would pop everytime we walked in and out of buildings.


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    #301
    Bears and Vodka
    Registered Users Posts: 2,249 ✭✭✭Bears and Vodka


    ECM2012 wrote: »
    In the nuclear physics question, if you multiplied the mass of an electron by the mass numbers of 3H and 2H without using the values in the log tables, would you say that's ok?

    No, because electrons don't come in to this question at all. They said nuclei.

    You will still be given marks for the formula and substituting in and for the unit :)


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