ELECTRO MAGNETIC RAIATIONS.pptx

ELECTRO MAGNETIC RAIATIONS

1. ELECTRO MAGNETIC RADIATIONS BY- SYED MASOOD

2. DEFINITION These are the waves in the sense that they consists of regular sinusoidal variations of electric & magnetic field at right angle to one another.

3. Electromagnetic radiation is classified according to the frequency of its wave. In order increasing frequency and decreasing wavelength , radio waves , microwaves , infrared radiation , visible light , ultraviolet radiation , X-rays and gamma rays Its also called electro magnetic spectrum. The eyes of various organisms sense a small and somewhat variable window of frequencies called the visible spectrum .

4. PRODUCTION E.M.R are produced by the movement of electrons within the atom. When any energy is added i.e by heat or stimulus . an electron to move out to a higher energy electron shell. When electron returns to the normal level the energy is release as a pulse of E.M.energy. Cause

5. ELECTRON ARRANGMENT. PRODUCTION OF EMR..

6. Properties of E.M.R Wavelength- A wave consists of successive troughs and crests The distance between two adjacent crests or troughs is called the wavelength . Waves of the electromagnetic spectrum vary in size- very long - Radio waves the size of buildings to very short gamma rays smaller than atom nuclei. Frequency is inversely proportional to wavelength v= f λ where v =speed of the wave f = frequency λ is the wavelength. As waves cross boundaries between different media, their speeds change but their frequencies remain constant.

7. Interference - Interference is the superposition of two or more waves resulting in a new wave pattern. If the field are in the same direction, they constructively interfere, while opposite directions cause destructive interference. The energy in electromagnetic waves is sometimes called radiant energy .

8. RECTILINEAR PROPAGATION radiations travel in straight lines in the space. Emr are emitted from their source in all direction. Obey inverse square law; I = 1/D 2 here I= intensity& D= distance.

9. PHASE DIFFERENCE- WHEN stimulated light emission i.e LASER is possible to make all the emitted atom radiate in one phase. COHERENCE- The peak & trough of electric & magnetic radiation travel in the same direction & same time.

10. REFLECTION- when an electromagnetic wave encounters a medium which will not transmit it. The ray is reflected back in the same plane such that Angle i= angle r.

11. Internal reflection- occurs when the angle i strikes an interface b/w the 2 media in such that instead of transition its reflected . This happens at the angles of incidence above a critical angle. This method is applied when U.V rays is applied to an internal cavity or an infected sinus.

12. REFRACTION- it occurs when E.M.R are transmitted from one medium to another with an angle of incidence GREATER THAN ZERO. Rays with a 0 angle of incidence i.e striking the surface at rt angles continue in the same line.

13. Acc to SNELL’S law- refraction occurs when the rays is deflected from its original course by an amount depending on the media involved & the angle of incidence. denser media= Refracted towards the normal. Less dense media = refracted away the normal. Less dense Dense Less dense

14. Refraction is imp when using hydrotherapy as a form of treatment. As the refraction of rays passing from water the air makes the position of object in water difficult to assess. the same is true when using water as coupling medium for ultrasound.

15. ABSORPTION- When E.M.R rays strike a new medium they may be absorb & produce an effect ( LAW OF GROTHUS). The proportion of rays depends upon- wavelength of rays. nature of medium. angle of incidence. There are following media that absorbs various E.M.R .

16. Window glass- visible light , IRR. WATER= IRR, visible, U.V. Soft tissue= X rays. Cello phone= short U.V rays. the angle at which the rays strike the surface also affects the proportion of absorption.

17. It depends on the COSINE LAW it states that the intensity of rays at a surface varies with the cosine of angle b/w the incident rays & the normal. Cosine 90= 0 no absorption. cosine 0= 1 max absorption Cosine 90= 0 no absorption. cosine 0= 1 max absorption

18. SCATTERING- Radiation passing in non homogenous matter may be partly scattered that is the direction of some rays is altered effectively reducing the depth of penetration. The scattered radiation may travel in difference direction & be absorbed at some point away from the main beam of radiation.

19. CAUSES- reflection. refraction. E.g.- U.V are strongly scattered in the skin decreasing their penetration. SCATTERING INC AS THE DEPTH INC .

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