comparison of values
2011-04-08 5:00 pm
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Q: I don't know how to handle with this type of questions ,what are the thinking sequences should I concern?
1st,I let P,t,m,l be the actual value of power,time needed,mass,specific latent heat and P',t',m',l' be the measured value,
2nd,as l=Pt/m,sub measured value
such as
statment (1),since energy lose ,then P=P',m=m',the time needed t'will larger than actual value t',therefore l' >l and (1) is wrong
statment (2),m>m',P=P',t=t',l'>l and (2) is wrong
statment (3),m=m',P<P',t=t',l'<l and (3) is correct
Are there anymore ans which is more efficient? plx help!
回答 (2)
2011-04-09 7:56 am
✔ 最佳答案
Your line of thought is basically right.Given that the experimental value is lower than the actual value would mean that the actual value is higher than the experimental value. Hence, from the relation:
L = Pt/m
[where L is the latent heat, P is the power of heater, t is the time taken, and m is the mass of ice]
(1) With heat lost to the surroundingsmeans the actual power used on melting the ice is smaller, thus a lower value of P should be used for accurate calaculation. Hence, the actual value of L is smaller than the experimental value. The statement is wrong.
(2) With larger mass of ice m in the equation, the actual value of L is lower than the experimental value. Thus the statement is wrong.
(3) With higher power P in the equation, the actual value of L is higher than the experimental value. Hence this statement is correct.
2011-04-09 4:38 am
Theoretical value of energy needed :
E = mass.latent heat
1) E=mass.latent heat
if energy lost to the surr.
E=(energy provided - energy lost)
Energy needed increase. (1) is wrong.
2)mass increase cause energy required to melt all the ice increase.
(E'=(0.1+x).latent heat)
E'>E. (2) is wrong.
3)E=pt
E'=(p+x)t=pt+xt=E+xt
In case(3), E' is the actual value of energy provided.
E<E', (3) is correct.
E = mass.latent heat
1) E=mass.latent heat
if energy lost to the surr.
E=(energy provided - energy lost)
Energy needed increase. (1) is wrong.
2)mass increase cause energy required to melt all the ice increase.
(E'=(0.1+x).latent heat)
E'>E. (2) is wrong.
3)E=pt
E'=(p+x)t=pt+xt=E+xt
In case(3), E' is the actual value of energy provided.
E<E', (3) is correct.
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