H_&_T[1]-1.pptx .gt76t7yt7yfugugyugjwxbzj cbvjfvbfjvgwrighwrighrwgbureigbjrv

Jhosidgvulbsuduvgrigvuub fgbhfu

1. HEAT & TEMPERATURE

2. Heat Heat is a form of energy transferred from a warmer body or system, to a colder one. Energy that is transferred from one body to another as the result of a difference in temperature So, one system releases heat and the other one absorbs it Units joules

3. Temperature Temperature is the thermal state of a body. which controls the flow of heat from one body to another & determines the direction on heat flow. Units Celsius Fahrenheit Kelvin

4. Physical effects of heat A number of physical phenomena result from increasing the kinetic energy of its microstructure. Rise in temperature: The average kinetic energy of constituent molecules increases. Expansion of the material: Increased kinetic energy produces a greater vibration of molecules, which move further apart and expand the material. Gases will expand more than liquids and liquids more than solids.

5. If, for example, a gas is enclosed so that expansion cannot take place, a rise in gas pressure will occur instead. 3. Change in physical state : Changing a substance from one physical state (phase) to another requires a specific amount of heat energy (i.e. Latent heat). 4. Acceleration of chemical reactions: Van’t Hoff’s law states that any chemical reaction, capable of being accelerated, is accelerated by a rise in temperature. Temperature directly proportional to acceleration of chemical action.

6. 5. Production of an electrical potential difference: If the junction of two dissimilar metals (e.g. Copper and antimony) is heated, electromotive force or electrical potential difference is produced between their free ends. Conversely, an e.m.f . Applied to the junction Of two metals can cause a rise in temperature at the junction

7. 6. Production of electromagnetic waves: When energy is added to an atom (by heating), an electron may move out into a higher-energy electron shell. When the electron returns to its normal level, energy is released as a pulse of electromagnetic energy. When first heated only a infrared electromagnetic waves are emitted, this can be felt as heat

8. 7. Thermionic emission: Heating Of some materials (like tungsten ) may cause such molecular agitation that some electrons leave their atoms and may break free of the metal. This leaves a positive charge which tends to attract electrons back. A point is reached where the rate Of loss of electrons equals the rate of return, and a cloud of electrons then exists as a space charge around the metal. This process is known as thermionic emission.

9. 8. Reduction in viscosity of fluids: Dynamic viscosity is the property of a fluid (liquid or gas) of offering internal friction to the non-accelerated displacement of two adjacent layers. The molecules in a viscous fluid are quite strongly attracted to one another. Heating increases the kinetic movement of these molecules, reducing their cohesive mutual attraction and making the fluid less viscous.

10. Latent heat Specific amount of energy is required to change the Salt from of a particular substance into the liquid or the liquid into a gas. This energy is called latent heat and it is the energy required for change of state Example 1 gram of ice converted to 1 gram of water at 0 centigrade requires 336 joules of energy – latent heat of fusion 1 gram of water at 100 degree centigrade requires 2268 doules of energy to convert it into one gram of Steam/ vapour- latent heat of vaporization

11. Transmission of heat It is natural that energy is always conserved. Cooling of a hot material can only be achieved by transferring heat energy to another place, or by converting it into another form. There are three ways of heat transfer; Conduction, Convection and Radiation.

12. Conduction This process occurs in most solids.Heat is transferred by direct contact. Solid are the best conductors of heat.
Transmission of heat from particle to particle. If one end of a solid metal rod is heated, the energy added causes and increased vibration of molecules. This vibration is transmitted to adjacent molecule and in this way heat is conducted along the bar from the area of high temperature to areas of low temperature.

13. Convection This process occurs in liquid and gases.
Heat is transferred by the movement of currents If one part of the fluid is heated, the kinetic energy of the molecules in the part is increased, they move further apart and these part becomes less dense Consequently it rises, displacing the more dense fluid above which descends to take its place. The current so produced or called convection currents.

14. Radiation Transfer of heat through electromagnetic waves. Contact between the source and the heated substance is not necessary. Heat maybe transmitted by infrared electromagnetic radiation. The heating of certain atoms causes electron to move to a higher energy electron shell as it returns to its normal, the energy is released as a pulse of infra-red electromagnetic energy.

15. PHYSIOLOGICAL EFFECTS OF HEAT

16. If any tissue is heated temperature rises which leads to some physiological changes of the tissue, they are Increase in metabolic activity Increase in blood supply Stimulation of neural receptors in skin or tissue. Skin changes Indirect effect of heat , General rise in temperature

17. Increased activity of sweat glands On muscle tissue leads to muscle contraction Efficiency of muscle action Muscle relaxation

18. Factors affecting Size of the area Death of absorption Duration of radiation Intensity Method of application

19. ELECTROMAGNETIC SPECTRUM

20. The electromagnetic spectrum is the full range of electromagnetic radiation, organized by frequency and wavelength. The spectrum is divided into separate bands, with different names for electromagnetic waves within each band. From low to high frequency these are; - Radio waves - Microwaves - Infrared rays - Visible light - Ultraviolet rays - X rays - Gamma rays

21. Wavelength The wavelength is the distance between a point on one electromagnetic wave and exactly the same point on the next wave. Wavelengths of; Radio wave : 1mm to 100km IRR : 750nm to 0.4mm Visible rays : 400nm to 750nm X-rays and gamma rays : 0.1pm to 100nm

22. Velocity The velocity is constant for all forms of electromagnetic waves, i.e., 3X10 8 m (300 000 km) – speed of light. Frequency Frequency is the number of complete waves passing any fixed point in one second. There is an inverse relationship between wavelength and frequency for electromagnetic waves. i.e., if one wave have a long wavelength it will require only low frequency, and a wave with short wavelength will require high frequency.

23. Laws Governing Radiation Infrared, visible and ultra-violet waves travel in straight lines until they encounter a different medium, when they may be transmitted , reflected or absorbed. 1. Reflection 2.Refraction 3. Absorption

24. Reflection A normal is a line drawn perpendicular to the surface of a medium at the point where an electromagnetic wave strikes. Angles of reflection or refraction are measured between the electromagnetic ray and the normal. Reflection occurs when an electromagnetic wave encounters a medium which will not transmit it. In this case the ray is reflected back in the same plane such that the angle between the incident ray and the normal equals the angle between the reflected ray and the normal.

25. If the incident angle is 0° (i.e., the radiation strikes the surface at right angles) then the angle of reflection is also 0° (the incident ray, normal and reflected ray all coincide). The laws of reflection are employed in the design of reflectors used for the re-direction rays towards an appropriate target. In infrared and ultra-violet lamps a parabolic reflector is normally used, as this avoids the danger of concentration of rays which occur with some shapes of reflector. A parabolic reflector collects all the rays travelling in an inappropriate direction and reflects them from its surface so that they eventually all emerge parallel.

26. It should be remembered however, that the majority of rays emitted forwards from these lamps come directly from the source and so diverge; only a small proportion are reflected in the se way.

27. - Internal reflection: Internal reflection occurs when the angle of incidence of a ray as it strikes an interface between two media is such that instead of being transmitted it is reflected. This happens at angles of incidence above a certain critical angle. Internal reflection in quartz rod and be emitted only from end. This method of application is used when ultra-violet is applied to an internal cavity or an infected sinus.

28. Refraction Refraction occurs when electromagnetic rays are transmitted from one medium to another with an angle of incidence greater than zero. Rays with a zero angle of incidence (i.e., striking the surface at right angles), continue in the same straight line. Snell’s law- Refraction causes the ray to be deflected from its original course by an amount depending on the media involved and the angle of incidence . When passing into an optically denser medium, the ray is refracted toward the normal.

29. When passing into a less denser medium, it is refracted away from the normal. Refraction is important while using hydrotherapy as a form of treatment, as the refraction of rays passing from water to air makes the position of objects in water difficult to assess. The same is true when using water as a coupling medium for ultrasound.

30. Absorption When electromagnetic rays strike an new medium they may be absorbed and thus produce an effect ( law of Grotthus ). The proportion of rays absorbed depends upon the wavelength of rays, nature of medium and angle of incidence. A filter is a medium which will absorb some electromagnetic waves whilst allowing others to pass. Window glass allows visible light and infrared rays to pass while absorbing (filtering out) ultra-violet rays Water absorbs infrared but allows visible and ultra-violet to pass.

31. X rays are passes through soft tissues onto a photographic plate, but are absorbed to a greater extent by bone. The angle at which the rays strike the surface also affects the proportion absorbed. Cosine law: It states that the intensity of rays at a surface varies with the cosine of the angle between the incident ray and the normal. cosine of 90° = 0 ; cosine of 0° = 1

32. Inverse square law: Electromagnetic waves being produced from a point source also obey the law of inverse squares. It states that “the intensity of rays from a point source varies inversely with the square of the distance from that point source”. Rays produced from a point source diverge from one another at a uniform rate. Eg ., a set no. of rays cover a square with sides of 1m at a distance of 1m from source.., at 2m they will cover a square with sides 2m long. The first square has an area of 1m 2 , whereas the second has an area of 4m 2 .

33. As same no. Of rays are striking both squares (ignoring atm. Absorption), then the intensity of radiation on smaller square will be four times that of on larger at any point. As UV lamps and some IR lamps act almost as point sources, the rays they generate obey the law of inverse squares. This means, the closer the patient is to the source, the greater is the intensity of radiation; the further away, the less the intensity. In certain situations moving the lamp closer will allow a shorter dose to be given.

34. Eg., if a dose of UV of 60sec at 100cm produces a certain effect, the same effect could be obtained in 15sec at a distance of 50cm i.e., one quarter of time at half the distance.