# Comparing the boil time for a copper and steel kettle

1. Aug 20, 2015

### gijoel

1. The problem statement, all variables and given/known data
Your friend prefers to use a glass kettle with a copper base. You notice that the water takes less time to boil when using this kettle compare to the stainless steel one. Explain the phenomenon behind this observation.

2. Relevant equations

3. The attempt at a solution

1. Heat is directly conducted from the base of the kettle to the water inside. The amount of heat that passes through the kettle base depends on the thermal conductivity of the material of the base. The thermal conductivity of an object is defined as “how many Watts of heat can be conducted through a one meter thickness of said material with a one Kelvin temperature difference between the two ends.” (Koolance, n.d.) giving a unit of W/(mK).

The thermal conductivity of copper is 401 W/(mk) and stainless steel is 16.3. Whilst glass’ thermal conductivity is 1.2 – 1.4. Thus copper conducts heat 25.1 times better than stainless steel, so more heat will flow through it for a given amount of time than stainless steel. Because glass’ thermal conductivity is approximately 286 times lower than copper the heat inside the kettle is trapped. Causing the water’s temperature to climb faster.

References:

Koolance, n.d., "Cooling 101: The Basics of Heat Transfer", viewed 20 August 2015, <http://koolance.com/cooling101-heat-transfer> [Broken].

Last edited by a moderator: May 7, 2017
2. Aug 20, 2015

### Staff: Mentor

And your question is?

3. Aug 20, 2015

### gijoel

Am I right? The lecturer is being a pain in the butt and vague on her questions. Plus she hasn't really covered thermal conductivity but has done specific heat capacity

4. Aug 20, 2015

### PeroK

Physics is concerned with the real world, you know. So, maybe you could answer a question like this using your knowledge of the real world. You probably have a reasonable grasp of thermal conductivity from knowing that: you can hold a mug filled with hot water, but not a glass for very long and if you touch a metal kettle or pan filled with hot water, you'll burn yourself instantly.

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