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  1. U

    Three levels laser

    Well surely the energy needed to excite the electrons to the 3rd level, is equal to the energy released as they drop back down to the 1st??
  2. U

    Sketch the curves y =|x| and y = 2 - x^2 on the graphs

    is that what its asking? if so how do i work that out, is it similar to the wa you work out whether a curve crosses the x-axis. thanks
  3. U

    Sketch the curves y =|x| and y = 2 - x^2 on the graphs

    1. Homework Statement Sketch on the same axis the graphs of y = |x| and y = 2 - x^2. For which values f x is the inequality |x| < 2 - x^2 2. Homework Equations 3. The Attempt at a Solution I don't really understand what it is asking me to do, i've sketched the two curves...
  4. U

    Gas Laws

    oh ok, so does that mean that the number of moles in 200g of CO2 is 0.2 (kg) / (6.02 x 10^32) all x 3 becuase there are 3 moles per molecule
  5. U

    Point charge and electric potential

    thank you. i think it was a typing error lol.
  6. U

    Point charge and electric potential

    1. Homework Statement three point charges, each of 10^-9 are located at 3 corners of a square of side 20cm. Calculate the electric potential at the forth corner. 2. Homework Equations V = Q / (4(pi)(epsilon 0) r) 3. The Attempt at a Solution Potential because of corner A =...
  7. U

    Gas Laws

    ok scrap that last post lol, 1 mole of carbon-12 is 12 grams, 1 mole of oxgen-16 is 16 grams, so i still need to know how much of the 200g is carbon. thanks
  8. U

    Gas Laws

    ok well the ratio of CO2 is 12:32 one mole of C is 6.02x10^23 x 12 one mole of O is 6.03x10^23 x 16 but how do i work out how much of the 200g is carbon? thanks so far!
  9. U

    Gas Laws

    1. Homework Statement A 200g sample of CO2 occupies a volume of 110 L at a pressure of 1 atm. a) What is the number of moles in the gas b) What is the temperature? c) if the volume is increased up to 200 L and the temperature is kept constant. what is the new pressure. 2...
  10. U

    Polar and cartesian form

    I just tried to sketch the curve whos form is r = cos(theta) but there is not curve!!?? when theta = 0, r = 1 when theta = (pi/2), r = 0 when theta = (pi), r = -1 ect so there is no curve!!! the point im finding are just on the x or y axis, or on the origin! am i doing something wrong.
  11. U

    Polar and cartesian form

    ok thanks, when doing cos(theta) woud theta be in radians or degrees?? thanks
  12. U

    Polar and cartesian form

    1. Homework Statement i) Express the equation r = 1 + cos(theta) in Cartesian form. ii) Sketch the curve whose equation in polar form is r = cos(theta) 2. Homework Equations x = r cos (theta) y = r sin (theta) 3. The Attempt at a Solution i) x = r cos (theta) = (1 + cos(theta)) cos...
  13. U

    Stupid question

    thankyou! and yes a) was suposed to be \overline{z} lol
  14. U

    Stupid question

    this will probably seem like a really stupid question but here goes. If z = 3 + 2i find the following i) z ii) z x z(with a horizontal line above it) iii) z^2 what does the horizontal bar mean, i can't find it in my reivsion books lol. Thanks
  15. U

    Electromagnatism - Find charge deos this sphere have

    Thanks for everyones help =) but i still cant get the corect answer: Q2 = ((F x r^2) / Q1) x (1/(4 x pi x epsilon 0)) Q2 = ((4.91x10^-4 x 3^2) / 10^-8) x (9x10^9) = 3.97x10^15 Above the question it is stated that (1/(4 x pi x epsilon 0)) = 9x10^9 i still cant see how im not getting [ 4.9...
  16. U

    Electromagnatism - Find charge deos this sphere have

    ok, ignoring (1/(4 x pi x epsilon 0)) for the minute F = ( Q1 Q2 )/ r^2 F / Q2 = Q1 / r^2 1 / Q2 = Q1 / (F x r^2) Q2 = (F x r^2) / Q1
  17. U

    Electromagnatism - Find charge deos this sphere have

    ah, stupid me! so Q2 = (1/(4 x pi x epsilon 0)) x ((Q1 x f) / r^2) Q2 = (9 x 10^-9) x (((1.0 x 10^-8) x (4.9 x 10^-4)) / 3^2) Q2 = 4.9 x 10^-3 i, getting closer but, the answer should be 4.9 x 10^-9 i thought it might be the units but they seem ok now
  18. U

    Electromagnatism - Find charge deos this sphere have

    i see what i've done, it should be in Kg not g so F = 0.00005 x 9.8 = 4.91 x 10^-4 ok well: F = x ((Q1 Q2) / r^2) so if i rearrange to get Q2 Q2 = (1/(4 x pi x epsilon 0)) x (Q1 / (r^2 x F) yes???
  19. U

    Electromagnatism - Find charge deos this sphere have

    1. Homework Statement The centre of a small sphere carrying a positive charge of 1.0 x 10^-8 C is fixed at 3cm above the centre of a small conducting ball, which had a negative charge and a mass of 0.05g. If the ball remains suspended, what charge does it have? Answer is [ 4.9 x 10^-9]...
  20. U

    Rates of change in volume.

    Ok i think i might have cracked the 1st bit now, dh/dt = -kh h = Ce^-kt ln h = -kt + A but i dont understand how to work out how long it will take to empty 1/2 of the water, there are no figures to work with? thanks for your help so far neutrino.
  21. U

    Rates of change in volume.

    the speed at which the height of the water decreases well the diffrence of the height from the initial value is h - h0 so the rate of change is dh / dt = (h - h0) / (t - t0) ?
  22. U

    Rates of change in volume.

    ok so: the rate at which water leaves the tank = -kh i'm a little confused about teh "discharge coefficient"
  23. U

    Rates of change in volume.

    1. Homework Statement A tank is in a shape of a cylinder with a circular cross-section of area A. Initially the depth of water in the tank (the head) is h0. At time t = 0 water is allowed to leave the tank ffrom a valve at the bottom. The rate at which the water leaves the tank is...
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