HEAT related consequences inside matter and medical physics..pptx

regarding sources of heat

1. HEAT BY SYED AMJAD HUSSAIN M.Sc. Dpt. QCHP Licensed Diploma in football medicine Certified orthopedic manipulative sports therapist

2. OBJECTIVES At the end of this chapter students able to identify General principles. What is heat. What is Temperature Scales of temperature and conversions. Heat capacity. Specific heat capacity Law of heat exchange. Heat transfers. Modes of heat transfers. Physiological and therapeutic effects of heat .

3. General principles

4. Heat Definition Transformation of a energy from an hot body to a cold body due to their temperature difference, when they are in thermal contact . Units S.I: joule CGS:CALORIE( cal ). 1 Cal=4.18J

5. Temperature Definition The physical property which determines the quantity and direction of heat flow between two bodies in thermal contact is called temperature. Or Measure of level of the heat Or Degree of hotness and coldness of a body Units kelvin Celsius degree Fahrenheit degree

6. Scales of temperature

7. Conversions of one scale to another

8. Temperature of a normal human body is 98.6F this temperature into Celsius is?

9. Law of heat exchange “Heat lost by hot bodies is equal to the heat gained by cold bodies” Expression Heat loss = heat gain If the right hand is immersed in hot water and left hand is immersed in cold water then both hands placed in tap water it feels cold to the right and hot to the left.

10. Heat capacity Definition The amount of heat required to raise the temperature of an object by a unit degree is called heat capacity . Expression If certain mass of substance absorbed a small amount of heat “delta Q” for raise in temperature “delta T” heat capacity as’ c’= delta Q / delta T Unit: j/k

11. Specific Heat capacity Definition The amount of heat required to raise the temperature of 1 kilogram of a substance by 1 degree K is called specific heat capacity Expression If mass “m” of a substance absorbs small amount of heat delta “Q” c = deltaQ / m*delta T unit j/ kg.k Specific heat of water = 4.2 j/kg/k

12. Heat Transfers Heat transfer one body to another through three ways : Conduction Convection Radiation

13. CONDUCTION Transferring of heat from place to place by kinetic motion of atoms and molecules being passed from one to next. Metals are the good conductors of heat and electricity. Thermal conductivity Jostling and knocking mechanism.

14. Example Application of ice packs and hot packs

15. Convection Convection is the heat transfer mechanism that occurs in a fluid due to gross movement of molecules within the mass of fluid. Occurs in liquid and gases Circulation of blood all over the body

16. Example Sweating Evaporation

17. Radiation Heat may be transmitted by electromagnetic radiation emitted from the surface of a body whose surface temperature is above absolute zero. The rate of emission from a surface also depends on the nature of the substance A perfect black body absorbs all the radiation

18. Transmission of Heat Conduction : If one end of a solid metal rod is heated, the energy added causes an increased vibration of molecules. This is transmitted and thus, heat is conducted from area of high temperature to area of low temperature. For example, metals. Convection : It takes place in fluids. If one part of a fluid is heated, the kinetic energy of the molecules in that part is increased, they move further apart and this part becomes less dense. As a result it rises, displacing the more dense fluid above which descends to take its place. The current produced is called convection current. Radiation : Heat may be transmitted by infra-red electromagnetic radiation. As a substance is heated, it causes the electron to move to the higher-energy shell. As it returns to its normal shell, the energy is released as a pulse of infra-red electromagnetic energy

19. Effect of impurities on melting and boiling points Impurities lowers the melting point and increase the boiling point.

20. Impurities decreasing melting point The solid phase of pure chemical is in in a stable crystal lattice structure. When an impurity is added, it weakens the original crystal structure due to its different shape and size. This makes it easier to break up the crystal with less force i.e. the now impurity containing structure will need less melting point to melt than the original chemical.

21. Impurities increasing boiling point The presence of impurities decreases the number of water molecules available to be vaporized during boiling. Hence more heat will now be required to boil the same solution that was boiling at a lower temperature prior to adding impurities.