Biophysics First Level: Heat and Thermodynamics

Biophysics First Level 2024-2025

• Course code: FAC-104
• Lecturers: Dr. Nermin Ali, Dr. Enas Lotfy
• Lecture number: 2
• Topic: Heat and Thermodynamics

Heat and Thermodynamics

• Thermodynamics: The study of the relationship between heat, work, temperature, and energy. It involves the transfer of energy between different systems and forms.
• Heat: A form of energy transfer caused by a temperature difference between a system and its surroundings.
• Temperature: A measure of the internal energy of a system, interpreted as the average kinetic energy of its particles.
• Thermal equilibrium: A state where two objects no longer exchange energy by heat or radiation if brought into contact.

Definitions

• Temperature: A measure of the internal energy of a system.
• Heat: Energy transfer due to a temperature difference.
• Thermal equilibrium: A state where no net energy transfer occurs between two objects in contact.

Zeroth Law of Thermodynamics

• Objects A and B are separately in thermal equilibrium with a third object C, then A and B are also in thermal equilibrium with each other.

Thermometers

• Devices for measuring temperature.
• Different types use varying physical properties (volume, color, dimension, resistance) which change with temperature.

Temperature Scales

• Different scales exist (Celsius, Kelvin, Fahrenheit)
• Each scale is based on two fixed points: the freezing and boiling points of pure water.

Temperature Scale Conversion

• Formulas for converting between Celsius, Kelvin, and Fahrenheit are provided.

Thermometers and Temperature Scales

• The relationship between temperature, molecular motion, and absolute zero are discussed.

Constant Volume Gas Thermometers

• Pressure increases with temperature at constant volume
• Absolute zero is the theoretical point where molecular motion stops (-273°C/0°K).
• Formulas for pressure and temperature relationship are presented

Clinical Thermometer

• Used for measuring human body temperature.
• Typical range 35-42°C
• Mercury is the liquid typically used
• The glass wall is thin, enabling quick response, reflecting rapid heat transfer

Platinum Resistance Thermometer

• Resistance changes with temperature
• Use the platinum wire in a Wheatstone Bridge.
• The resistance (R) changes proportionally with temperature (T) in relation to other constants.
• Large temperature range is a key advantage (-250°C to 1250°C).

Thermocouples

• Generate an electromotive force (EMF) when dissimilar metals are in contact.
• The magnitude of the EMF depends on the temperature difference.
• Useful for temperature measurement.
• Often include two wires of different metals joined together, connected to a voltmeter

Simple Thermocouples

• Several configurations can measure temperature using different metal pairings.
• Readings on a voltmeter increase as temperature rises.

Advantages of Thermocouples

• Wide temperature range (-200 to 1500°C)
• Easy to use and inexpensive
• Can measure rapidly fluctuating temperatures.