? 發問於 科學及數學其他 - 科學 · 1 十年 前

physics.heat problems!please!quite urgent.

there are lots of qustions asking that "the result obtained will be larger or smaller than the true value of x if....."

i dunno why i'm always wrong in answering this type of question

i really so confused.

for example:

there's an experiment to find the specific latent heat of vaporization of water

determine if the result obtained will be larger or smaller than the true value of l(v) if

(i) measurement is started before the water boils

(ii)some steam condenses and drips back into the beaker

(iii) some boiling water inside the beaker splashes out of the beaker

answer(i) is larger

as E=ml and E=pt, doesnt it mean l=pt/m?

in situation (i),i understand this one

measurement starts earlier and measured energy is larger

so l becomes larger at the same time

answer(ii) is larger

i dont understand this one because as the mass becomes larger

is that l will become smaller too?(l=E/m)

answer(iii) is smaller

and yes i understand this one too

but how about (ii)?

1 個解答

評分
  • 天同
    Lv 7
    1 十年 前
    最佳解答

    When evapourated water condensed and dripped back into the beaker, the final mass of water left in the beaker is larger than it should be if no condensation occurred.

    Since m in your equation is the mass of water evapourated, which is calculated by subtracting the final mass from the initital mass of water in the beaker,

    i.e. m = mass(initial) - mass(final)

    Since latent heat = energy supplied E/m

    now, because m(finial) is larger, then m becomes smaller than it should be. The calculated latent heat is larger than the actual value.

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