Unit 1: Thermal Physics (Lab: PHYDSC253P)
Table of Contents
- 1. Laboratory Objectives & Overview
- 2. Mechanical Equivalent of Heat (J)
- 3. Thermal Conductivity of a Good Conductor (Searle’s Method)
- 4. Coefficient of Linear Expansion
- 5. Thermal Conductivity of a Bad Conductor (Lee’s Disc Method)
- 6. Platinum Resistance Thermometer (PRT)
- 7. Variation of Thermo-emf with Temperature
- 8. Specific Heat of a Liquid (Method of Cooling)
- 9. Lab Exam Focus Corner
1. Laboratory Objectives & Overview
The primary objective of this course is to provide students with hands-on experience in using thermal measurement instruments and estimating various physical parameters. Students will learn to perform experiments related to thermal physics, analyze results, and report findings with accuracy.
2. Mechanical Equivalent of Heat (J)
This experiment involves determining the value of 'J' using either Joule's Calorimeter or Callender and Barne’s constant flow method. The goal is to establish the ratio of work done to the heat produced.
Principle: When work is converted into heat, the amount of heat produced is proportional to the work done.
3. Thermal Conductivity of a Good Conductor (Searle’s Method)
The coefficient of thermal conductivity of a good conductor like Copper (Cu) is measured using Searle's Apparatus. In this method, heat flows through a rod under steady-state conditions, and the temperature gradient along the rod is measured.
Key Procedure:
- Steam is passed through one end of the rod while water flows through a coil at the other end.
- Temperature is measured at four points using thermometers once steady-state is reached.
4. Coefficient of Linear Expansion
The coefficient of linear expansion of a metal rod is determined using the optical lever method. This method allows for the measurement of extremely small increases in length as the temperature of the rod increases.
5. Thermal Conductivity of a Bad Conductor (Lee’s Disc Method)
For bad conductors (like ebonite or glass), the Lee and Charlton’s disc method is used. Since bad conductors do not allow for easy steady-state heat flow, this method uses a thin specimen disc between a steam chamber and a metallic base disc.
6. Platinum Resistance Thermometer (PRT)
This experiment focuses on determining the Temperature Coefficient of Resistance using a PRT. It utilizes the principle that the electrical resistance of a platinum wire increases linearly with temperature.
7. Variation of Thermo-emf with Temperature
Students study the variation of Thermo-emf of a Thermocouple with the temperature difference between its two junctions. This experiment explores the Seebeck effect and establishes the relationship between temperature and generated voltage.
8. Specific Heat of a Liquid (Method of Cooling)
The specific heat of a liquid is determined by comparing its rate of cooling to that of a known liquid (usually water) under identical conditions. This is based on Newton’s Law of Cooling.
Lab Exam Focus Corner
Frequently Asked Questions
- What is 'Steady State' in conductivity experiments?
It is the state when the temperature at every point of the rod remains constant with time. - Why is Lee's Disc method used specifically for bad conductors?
Standard methods like Searle's require high heat flow, which bad conductors cannot maintain. Lee's method uses a thin disc to minimize thermal resistance.
Common Mistakes
- Parallax Error: Not reading thermometers at eye level, leading to inaccurate temperature gradients.
- Steady State Assumption: Starting observations before the apparatus has truly reached thermal equilibrium.
Lab Tips
Tip: Always ensure the cooling calorimeter is well-polished to maintain constant emissivity when performing the method of cooling. For PRT, make sure all connections are tight to avoid contact resistance.