Physics: Heat & Thermodynamics (AP Physics and High School)

So, recall a time when you saw your mother open the tight lid of a glass jar by putting it under warm water. Well why did the lid magically open. I’m sure your mother was a “wonder woman” but she also knew a bit of physics of opening jars. Well, what happened here was that the glass and the lid both expanded under warm water but the lid expanded a little more than the glass and therefore loosened up and opened.

Welcome back to another interesting lesson and what we will learn here is-

1. What is heat in context of system and its environment

2. When is heat considered positive or negative

3. Absorption of heat by solids and liquids

4. What is heat capacity

5. What is specific heat capacity

6. What is molar specific heat capacity

So we seem to have our hands full but let me tell you that this is an easy lesson but still I would like you to be all ears

Great to have you back! And before we get into the laws of thermodynamics, let us do some preparation for it. So in this lesson we will cover

1. What are PV diagrams

2. What is work done by a system

3. What is heat in or out of the system and

4. What is the internal energy of a system

Well, We will also cover various kinds of thermodynamic processes

So we have been talking all through the last three lessons about transfer of energy between the system and the environment but not really discussed how “exactly” does this transfer take place

So what we will learn in this lesson are three ways in which heat can move between the system and the environment and vice versa and three mechanisms are conduction, convection, and radiation.

Great to have you back in another lesson on heat.. and Kinetic theory of gasses is one of the mainstream topics in physics…so what we will learn in this lesson is what is Avogadro’s number, what is the relationship between the number of moles n, number of molecules N and Avogadro’s number Na, we will learn the Ideal gas law, relate the ideal gas constant R and the Boltzmann Constant k, learn what are isotherms and finally work on the PV diagram for various processes

So this brings us to another very interesting part of this chapter and that is the RMS Speed or the root mean square speed of a molecule of a gas. Well, it may sound complicated but stay with me and you’ll see that it is not as complicated as it sounds.

So this brings us to the topic of translational energy or simply put kinetic energy of a molecule and what we will learn in this lesson is

1. What is the kinetic energy of a molecule expressed as a function of temperature T and two

2. What is the concept of mean free path or the distance covered by a molecule before it collides with another

Great to have you back and today we will study “the Distribution of Molecular speeds” which I think is a very interesting topic. So what we will learn in this lesson is …how do we find “what fraction of molecules are in a certain speed range” and if we can figure out a way to do so, then more specifically, what fraction of molecules are moving around at average velocity, what fraction is moving at rms velocity and what fraction of molecules is moving at most probable velocity… and do not get lost here, you will be quite clear by the end of the lesson

So this brings us to another topic that we have studied earlier also and that is Molar specific heats of an ideal gas. The difference is that this time around we will derive the formula for internal energy of a gas by studying the gas at a molecular level and how the random motion of the molecules results in the gas getting its internal energy

So welcome to another lesson where we will establish the equation PV^ gamma is a constant in an adiabatic process where gamma is the ratio Cp/Cv

From the lessons we have studied so far, we can say that there are several thermodynamic processes that proceed naturally in one direction but will not reverse themselves. The most common one is heat flow from a hot to a cold body where we never see the reverse happening

So with what we have learnt so far, its time we got into some more interesting stuff and that is “the Carnot engine”. So what we will learn in this lesson is one how a Carnot engine works and two, how the efficiency of a Carnot engine is dependent on the temperature of the hot and cold reservoir only.

Well, refrigerator are also heat engines, contrary to what it does, that is cooling, and they actually operate in the reverse of what a typical heat engine would operate.

So let us go ahead now and study what is entropy and what is the quantitative relationship it has with heat flow Q and temperature T

So the flow of heat from a higher to a lower temperature is characteristic of a natural irreversible processes…and if you consider entropy change in every step in such a process… and add them up, you’d see, all in all entropy increases… but in all reversible processes any increase in the entropy will get cancelled by an equivalent decrease in entropy elsewhere and hence the net entropy change is always zero.

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