5. Measuring the mechanical equivalent of heat is difficult...

5. Measuring the mechanical equivalent of heat is difficult because heat capacities are so large. (a) How much heat is required to raise the temperature of 2,000 kg of water from 10°C to 45°C? This is similar to a medium-sized Japanese family bathtub. (b) I wanted to generate this heat by working, and I know that a person can sustain about a 250 W power output. How long would it take me to heat the water? (c) If the heat capacity is so large, why can't we use the heat in the lake water to power the electrical fixtures in a house?

Transcript

00:01 Here in this question, best you look at a distribution of experiment to measure the specific heat of some materials, right? let's look at this experiment.

00:13 So it's really about specific heat, right? specific heat measurement, right? and for you're convinced, i would like to copy down the, there's a picture, this diagram showing the experiment.

00:27 So let me copy down here.

00:31 That's just the diagram we have from the question.

00:37 Let me make it clear here.

00:40 So here is the question.

00:43 So basically this student who wants to measure basically heat capacity of some metal, right? so the matter is somewhere here, right? that's a matter.

00:51 And the matter of usually immersed in some water, immersed in the water.

00:57 It's hidden in boiling water, and it has reached the boiling temperature, right? so basically you have this boiling water and it immersed this metal in this boiling water.

01:11 And of course, in the boiling water where lower temperature and then stops boiling and then you have to heat it up again and then starts boiling again.

01:22 So you have a sensitive, obviously you will have a sensitive somometer to measure the initial final temperature of.

01:32 In the cup, right? that's basically what's happily.

01:39 So, you know, the business medicine runs is reasonable water and then transfer rapidly to some water and you wear insulated cap.

01:50 Oh, so what's happening is this, you have this boiling water, you immerse this matter in the water, and it boiled up.

01:59 So the temperature, the meter has a temperature, which is, of course, the same as the boiling water.

02:03 That's 100 degrees.

02:05 And, then you quickly transfer this metal into a different carp, which is well insulated by a wall, and then you measure temperature, right? this is also water.

02:15 And of course, you measure how the temperature rises when the metal is cooled down.

02:22 So the reading is from the sped mass forest.

02:24 The metal has a mass 50 grams, mass of water in the cup is this much.

02:29 Initial temperature of water in the cup is this, and the final temperature is this much.

02:35 So, and while you, for you convinced, we can we can convote this temperature into caravans, right? so i think you just might, you just sum, you just add by 270, right? 270 caravons...

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