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  1. S

    ---> Physics Paper 4 Past Paper Discussion <---

    But since they're both in opposite directions, wouldn't that mean that they cancel each other out? Because that's what the top answer on this Yahoo Answers page says: http://answers.yahoo.com/question/index?qid=20120322031104AAaEyQJ
  2. S

    ---> Physics Paper 4 Past Paper Discussion <---

    Yes, that is right, in the middle an electron would experience equal attraction from the two positive charges and a proton would experience equal repulsion from the same two charges and thus the net force (and the net field strength) would be equal to zero. If they ask the question with a...
  3. S

    ---> Physics Paper 4 Past Paper Discussion <---

    9) a) i) The point is at the connection of the wire coming from the output to the inverting input - this is the point at which the net potential is virtually zero. ii) An op amp has a huge gain, and if the op amp is not saturated, the difference between the inverting potential and the non -...
  4. S

    ---> Physics Paper 4 Past Paper Discussion <---

    We did the same question in class, it's a pretty confusing one! In the question, it is mentioned that the needle undergoes S.H.M, and i'm quite sure we're just supposed to take it up blindly and go along - For all you know, it might be the cloth that is provided the force required for S.H.M...
  5. S

    Chemistry: Post your doubts here!

    Thanks a load for the earlier answer, it sure did clear up a lot! I really wonder where SiO₂ does not react with NaOH - the textbook definitely mentions a reaction occurring, Wikipedia mentions a reaction occurring, and general concepts do confirm that! If, indeed, the acidity of the Group IV...
  6. S

    ---> Physics Paper 4 Past Paper Discussion <---

    The graph starts off quite high on the y axis (but not at x = 0, at "surface of Earth") and decreases as a curve till a point closer to the "surface of Moon" than the "surface of Earth", at which point it goes to zero. Then it changes polarity (positive to negative of negative to positive, both...
  7. S

    Chemistry: Post your doubts here!

    Neat, thanks a lot! Good Luck for all your exams!
  8. S

    Chemistry: Post your doubts here!

    Then how are we supposed the do Question 3 (c) for the following paper: The first two solutions I can understand, Fluorine and Sulfate are not released, but why does the marking scheme say Bromine is released at the anode? is it because of the lack of standard conditions or is it some other...
  9. S

    ---> Physics Paper 4 Past Paper Discussion <---

    I'm not really sure, but the examiners report said that the students who obtained the answer counted squares (individual small squares or 1 cm^2 squares) or drew a series of strips that covered the entire area under the curve. The answer is 3300 microCoulombs, and it would be pretty difficult to...
  10. S

    ---> Physics Paper 4 Past Paper Discussion <---

    Thanks a lot for the kind words, but I really owe all of you guys a load, most of the questions posted here came from papers I probably wouldn't have checked - the 2007 paper, the 2008 paper, the specimen paper, 2011 paper 43 (our school does variant 42) - checking out these questions has...
  11. S

    Chemistry: Post your doubts here!

    Guys, I just have a question - In the electrolysis of aqueous solutions containing halide ions, how do we determine using standard electrode potential values (E nought values) what is produced at the anode? Assuming that conditions are all standard and concentration doesn't have a role to play...
  12. S

    Chemistry: Post your doubts here!

    For the 2007 specimen, 9 (b) & (d): The first clue is the empirical formula calculated for the earlier part question; it is C8H10O, and since the number at the top of each peak, that describe the number of hydrogen atoms per group, add up to 10, it looks like the molecular formula is also...
  13. S

    Physics: Post your doubts here!

    In short, yes, the energy of all waves in the electromagnetic spectrum is carried by the photon; it is the quanta of electromagnetic radiation, and as such it carries the energy possessed in every wave, and it interacts with other particles by transferring this energy, etc. In fact, electrons...
  14. S

    ---> Physics Paper 4 Past Paper Discussion <---

    I should be thanking you - it's the first time I had seen the question, and I got it wrong when I first tried it - I had forgotten to include the 10^4 thing, and had thus gotten it wrong, so thank you for reminding me how important powers of 10 are! Good Luck for all your exams!
  15. S

    ---> Physics Paper 4 Past Paper Discussion <---

    A piezoelectric crystal coupled with a receiver is also used to measure distances; it's the centerpiece of ultrasound production and detection and it's also used in SONAR (or, at the very least, the same principle is used in SONAR as for Ultrasound). The pulse is released, and if the machine...
  16. S

    ---> Physics Paper 4 Past Paper Discussion <---

    Not at all too much work, here it is: First things first: all meters! Practically every formula in the syllabus would be defined for SI units alone, so they've given you values in kilometers; these need to be converted! Anyways, it is said that the object is moved from the surface of the Earth...
  17. S

    ---> Physics Paper 4 Past Paper Discussion <---

    Measure the length of what?
  18. S

    ---> Physics Paper 4 Past Paper Discussion <---

    If you are considering the altitude above the surface above a planet/moon/other celestial body, the matter can be simplified pretty quickly In any individual body, there are a huge number of particles; suppose you have to find out the force of attraction due to gravity between the Earth and a...
  19. S

    ---> Physics Paper 4 Past Paper Discussion <---

    The question has stated that the mean kinetic energy of an ideal gas molecules at a particular temperature is given by that equation. In any sample of a gas, at any temperature, there will be a massive number of molecules/atoms interacting with each other by means of random collisions - there is...
  20. S

    ---> Physics Paper 4 Past Paper Discussion <---

    Sure, here's the method: There's a formula that relates the amplitude, displacement and angular frequency of the mass undergoing simple harmonic motion to its velocity: V = Angular Frequency * sqrt(Amplitude^2 - Displacement^2) Note that the root can be positive or negative, so there are...
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