Question:
. A metallic coil connected to a 220V supply has a resistance of 110 ohm. How long will it take this coil to heat 1kg water from 20 C to 70 C
Answer:
Heat produced by the metallic coil = Heat taken up by water.
We know,
H = V2/R x t
And, also H = mCpΔt
So, V2/R x t = mCpΔT
Therefore, t = mCpΔT x R/V2-
Cp for water = 4.186 J/(g.K)
t = 1000g x 4.186 x (70 - 20) x 110/(220)2
= 475.7 secs
= 7.92 minutes.
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