Biophysics: Heat and Thermodynamics

Biophysics: Heat and Thermodynamics

• Thermodynamics is the study of the relationship between heat, work, temperature, and energy.
• It deals with energy transfer between places and forms.
• Heat is a form of energy corresponding to a definite amount of mechanical work.

Definitions

• Temperature is an interpretation of the amount of internal energy in a system.
• Heat is the transfer of energy across a system boundary due to temperature differences between the system and its surroundings.
• Thermal equilibrium is a state where two objects won't exchange energy (heat or electromagnetic radiation) if placed in contact.

Zeroth Law of Thermodynamics

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

Thermometers

• Devices used to measure temperature.
• Utilize a physical property (e.g., volume, color, dimension, resistance) that changes with temperature.

Temperature Scales

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

Temperature Scale Conversion

• Celsius (°C), Kelvin (°K), and Fahrenheit (°F) are interconnected.

  • Conversion Formulae:
    • TC = TK - 273.15
    • TK = TC + 273
    • TF = (9/5)TC + 32

Constant Volume Gas Thermometers

• Pressure of a gas increases with temperature at a constant volume.
• Ideal gas equation (at constant volume): P = constant x T
• Absolute zero is the point where pressure equals zero (-273°C).

Clinical Thermometer

• Used for measuring human body temperature.
• Uses mercury inside a thin glass bulb.
• Rapidly indicates body temperature due to its thin wall and liquid configuration.
• Temperature range measured is 35-42°C

Platinum Resistance Thermometer

• Measures temperature based on the resistance of a platinum coil.
• Resistance changes proportionally with temperature.
• Formula: R= R (1 + αθ + βθ²)
• Advantage: Highly accurate and works over a wide temperature range (-250°C to +1250°C).

Thermocouples

• Created by contact of two dissimilar metals
• Produces an EMF (electromotive force).
• The magnitude of the EMF depends on the temperature difference at the contact point.
• Useful for rapidly changing temperatures.

Advantages of Thermocouples

• Wide measuring range (-200°C to 1500°C)
• Inexpensive and easy to use,
• Can be used for rapidly fluctuating temperatures