Medical Biophysics Lecture Notes 2025 PDF

Medical Biophysics Dr. Mahmoud Ismail  Heat energy heat Vs temperature zeroth low of thermodynamics temperature scales heat transfer  Heat is a type of energy  it gives indication about the kinetic energy of the system.  Temp.  kinetic E. while Temp.   kinetic E.  Temperatur...

Medical Biophysics Dr. Mahmoud Ismail  Heat energy heat Vs temperature zeroth low of thermodynamics temperature scales heat transfer  Heat is a type of energy  it gives indication about the kinetic energy of the system.  Temp.  kinetic E. while Temp.   kinetic E.  Temperature difference ΔT  Heat transferred. Heat: is the energy that is transferred between objects because of a temperature differences. Thermal equilibrium After objects in thermal contact with each other reach the same temperature, we say the objects are in thermal equilibrium.  Temperature Temperature: it is a measure of the average kinetic energy of the moving molecules. Note: Temperature is not measure the total kinetic energy of all the molecules in the substances. E.g: 2 liters of water have total kinetic energy =100 j And 1 liter of water has total kinetic energy =50 j The temperature are the same because the average kinetic energy of molecules in each is the same. Note: At -273 C0  molecules have the minimum possible amount of kinetic E  absolute zero Zeroth law of thermodynamics Zeroth law of thermodynamics states” if object A is in thermal equilibrium with object B , and object C is also in thermal equilibrium with object B , then object A and C will be in thermal equilibrium when they are in contact”.  The zeroth law therefore enables us to use to compare the temperatures of any objects we like. To read thermometer, we wait until it reaches thermal equilibrium with the substances being measured. Temperature scales There are three scales for temperature: Celsius scale. Fahrenheit scale. Kelvin scale. scale conversion 9 From Celsius (C) to Fahrenheit (F): TF  ( )TC  32 5 5 From Fahrenheit (F) to Celsius (C) : TC  (TF  32) 9 From Celsius (C) to Kelvin (K): TK  TC  273.15 From Kelvin (K) to Celsius (C): TC  TK  273.15 Q:What are the units of heat energy? A: (Joule, calorie, BTU). Joule: is the SI unit of all forms of energy.  Definition: calorie : is the amount of heat needed to raise the temperature of 1g of water by 1ᵒC (14.5 ᵒC to 15.5 ᵒC ).  Notes:  1C= 1Kcal.  1cal=4.18 J.  Definition: British thermal unit(BTU): is the amount of heat needed to raise the temperature of 1lb of water by 1 ᵒF.  A 70Kg person eat candy bar has an energy content 300 C, how many stairs must he climb to work off the energy of this candy bar, given that each stair is 25cm? Solution: Q=300C=300kcal=300x103 cal. Q= (300x103)x(4.186)=1.25x106J Q=mgh h=Q/mg =(1.25x106)/(70x9.8)= 1822 m The number of stairs=1822/0.25= 7288 stairs. Specific heat of water Specific heat capacity of water =4186 J/Kg.K (high value) means:. 1. Water has higher capacity to store heat Energy 2. Water take large quantities of heat with little change in temperature Heat Capacity and Specific Heat Phase change and latent heat Heat exchange: Heat can be exchanged by conduction, convection and radiation. conduction Conduction transfers heat energy in solids.  The moving particles of a warm soild material can increase the heat energy of the particles in a cooler solid material by transferring it directly from one particle to the next. Since particles are closer together, solids conduct heat better than liquids or gases. convection  convection Convection transfers heat energy through gases and liquids. As air is heated, the particles gain heat energy allowing them to move faster and further apart, carrying the heat energy with them. Warm air is less dense than cold air and will rise. Cooler air moves in below to replace the air that has risen. It heats up, rises, and is again replaced by cooler air, creating a circular flow called a convection current. These currents circle and heat the room. convection The worm portion of the fluid raise because of their lower density. In convection, temperature differences result in flow of fluid. Newton's law of cooling Radiation The energy radiated by the heated object is in the form of electromagnetic waves (infra-red (IR)). Stefan Boltzmann law Application on heat exchange The double walled insulating container (thermos bottle) invented by James Dewar. Shiny interior: no heat transferred by radiation. Vacuum between the inner and outer wall: no heat transferred by convection. Double walled: no heat transferred by conduction.