FreedomJustice

The resistance of an alloy wire is 25 when it is placed in a cup of melting ice. At room temperatureof 28(temp),
the resistance is 38.If the wire is put in boiling water, what will be the resistance
A:28
B:46
C71
D152

[ 本帖最後由 鍾倩怡 於 2006-11-10 11:29 PM 編輯 ]

二五仔

oops:O我唔識＝．＝”

Eraser

Suppose the change in resistance of the alloy have a linear relationship with the change in temperature:
At 0 degree (in melting ice) , resistance is 25
At 28 degree, resistance is 38
At 100 degree (boiling water), resistance is x
from 0 degree to 28 degree, the change in  temperature is 28-0 = 28
                                             the change in resistance is 38-25 = 13
for every degree change of temperature, the change in resistance = 13/28 = 0.46
from 0 degree to 100 degree, the change in temperature is 100-0 = 100
                                               the  CHANGE in resistance is 100*0.46 = 46
x = 25+ 46 = 71
Hence the answer is C 71