中三 phy急問

S!u笨寶

A 1500-W electric kettle is used to heat 2kg of water . The temperature of the water rises from 20度to 95度 in 7.5minutes

(a)How much energy is supplied by the kettle?

(b) assume that no energy is lost to the surroundings. how much energy is absorbed by the kettle?

俠4仙仔

(a) 1500*7.5*60 = 675000J = 675kJ
(b) 4200*2*(95-20) = 630000J = 630kJ

S!u笨寶

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咁如果佢問
How much energy is absorbed by the water 點計~

Jxm

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同#2計法一樣,因為佢用的specific heat capacity 就係水的specific heat capacity

我記得果陣中四先學heat, 現在中三就要學la

S!u笨寶

Jxm 發表於 11-10-23 09:48 PM
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同#2計法一樣,因為佢用的specific heat capacity 就係水的specific heat capacity

姐係點-o-吾多明

條式係點~

Jxm

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因為佢用緊 E = mc△T

E係energy, m係mass, c就係specific heat capacity, △T 係temperature change

4200*2*(95-20) = 630000J = 630kJ

實際上就係 c=4200(水的specific heat capacity) , m = 2kg (題目畀) ,△T=(95度-20度) (又係題目畀)
所以佢其實就係計緊energy absorbed by water

但題目寫明assume that no energy is lost to the surroundings.
所以energy absorbed by water= energy absorbed by the kettle

kscciz

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