You are boiling pasta and absentmindedly grab a copper stirring spoon rather than your wooden spoon. The copper spoon has a 20 mm × 1.5 mm rectangular cross section, and the distance from the boiling water to your 35∘C hand is 18 cm. How long does it take the spoon to transfer 40 J of energy to your hand?

It takes 9.23 seconds to transfer 40 J of energy from copper spoon to hand.

The time can be calculated by the thermal conductivity formula,

Where,

Q - amount of heat energy transferred = 40 J

A - cross section area of copper spoon = 20 x 1.5 = 30mm

k - thermal conductivity coefficient of copper = 400 W /mK

L - length of spoon = 18 cm,

- temperature difference = 100-35 = 65

put the values in the formula, and solve it for t,

Therefore, it takes 9.23 seconds to transfer 40 J of energy from copper spoon to hand.

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The spoon to transfer 40 J of energy to your hand is descibed as follows

Explanation:

Given  area of cross section of copper spoon is A = 20mm into 1.5 mm

temperature difference is DT = (100 minus 35) = 65 0C

length of the spoon is l = 18 cm,

amount of heat should be transfer Q = 40 J

coefficient of thermal conductivity of copper k = 400 W by mk

we know that the thermal conductivity is Q by t = k into A into DT by l

t = Q into l by k into A into DT

t = (40 into 0.18) by  

t = 9.23 s

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