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    HELP!!!! I need urgent help.
    Two issues:
    One, when they ask for the initial number of nuclei, and you have worked out the decay constant, λ, already, you use the formula:

    delta N/delta t = -λN

    but in all the exam questions, when that comes up, they just use the initial activity for (delta N/delta t). Isn't that wrong? Cuz i usually use N at a single half life, so N is half of the original activity, and t is a half life. But thats wrong. WHHY?????????????????????

    Two, does anyone know what questions came up on Paper A of Jan 05, cuz I was not in school for the mocks, and my class mates are all stupid, lol.

    Please help me out, exam is in like 36hours and im stuck .

    U know the equation N/N0=E^-lambda t? Well the N.No is the half life when you remove the base e so ln2=lambda T, and that T I think is is the time taken for half(ln2) to have disintergrated), so lets say they give you the rate of decay, ie lambda, to find time, u divide ln2 by lambda to get time taken, i still havent found any past paers asking for the half life!!! If i aint helped, go to and look at the stuff they've got.

    The two equations I would use, as said above would be:

    I personally, doing A2 Salters Horners, have never seen a question asking for the half life, they all seem to ask the fraction left after a certain time or the nuclei left after a certain time.
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