Lecture 2 Electromagnetic spectrum(1).pdf

Electromagnetic spectrum What is the EM Spectrum? Electromagnetic spectrum in simple terms is defined as the complete range of all types of electromagnetic radiation placed in order according to frequency or wavelength. Even though all EM waves travel at the same speed, they...

Electromagnetic spectrum What is the EM Spectrum? Electromagnetic spectrum in simple terms is defined as the complete range of all types of electromagnetic radiation placed in order according to frequency or wavelength. Even though all EM waves travel at the same speed, they have different wavelengths and frequencies. The electromagnetic spectrum (EM spectrum) is made up of radio waves, microwaves, infrared waves, visible light, ultraviolet rays, X-rays, and gamma rays. An electromagnetic spectrum 1 Electromagnetic radiation production:  Electromagnetic radiation is made when an atom absorbs energy. The absorbed energy causes one or more electrons to change their location within the atom. When the electron returns to its original position, an electromagnetic wave is produced.  Depending on the kind of atom and the amount of energy, this electromagnetic radiation can take the form of heat, light, ultraviolet, or other electromagnetic waves.  There are several ways of causing atoms to absorb energy. One way is to excite the atoms with electrical energy. The electricity will excite or add energy atoms. This said to be the atom in an excited stage.  The electrons don't like to be in the high energy state and will fall back down into the low energy state  When the electron returns to its normal level, energy is released due to the difference in levels as a pulse of electromagnetic radiation called a Photon. Electrons are the -ively charged particles that revolve around the +ively charged nucleus of an atom in specific orbit or levels in the ground state. 2 Theoretical characteristics of electromagnetic radiation 1- All electromagnetic waves have a constant velocity in space 3×108m/s (speed of light). 2- Their direction of travel is always in a straight line. In spite of the constant velocity of electromagnetic radiation, it differs in wavelength (λ) and frequency (f). Velocity of light (v) = frequency (f) × wave length (λ) v= λ x f Because the velocity of light is constant, there is an inverse relationship between wavelength and frequency for electromagnetic wave (the higher the frequency the shorter the wavelength). The relationship between wavelength and frequency for electromagnetic wave Which electromagnetic spectrum has the highest wavelength? The radio waves have the lowest frequency and the longest wavelength. Which part of the electromagnetic spectrum has the highest frequency? Gamma rays have the highest frequency and the shortest wavelength. 3 3- They may be reflected, refracted, or absorbed depending on the specific medium that they strike. Laws Governing Radiation Radiation: It is a process by which electromagnetic energy travels from its source outward through space. Radiations may be reflected, refracted, or absorbed in the various tissues. 1-Reflection Reflection occurs when electromagnetic waves encounters a medium which will not transmit it. In this case, the ray is reflected back into the same plane. 4 Clinical applications 1-In infrared and ultraviolet 2-In US therapy, (tissue air interface) Reflection of electromagnetic waves 2- Refraction Refraction occurs when electromagnetic rays are transmitted from one medium to another with different density and an angle of incidence greater than zero. 5 Clinical application: using water as coupling media as in ultrasound modality. Refraction of electromagnetic waves 3- Absorption: - When an electromagnetic wave strikes a new medium and travels through the medium, they may be absorbed and thus produce an effect (Heat), and the amount of rays absorbed depends on strength , frequency of the electromagnetic fields (The higher the frequency of the electromagnetic field the stronger the absorption at the body surface) and on the properties and structures of the biological tissue.. 6  Significance of Electromagnetic Spectrum The main significance of the electromagnetic spectrum is that it can be used to classify electromagnetic waves and arrange them according to their different frequencies or wavelengths. Practical Applications of Electromagnetic Waves Applications Electromagnetic waves play a vital role in our daily lives, especially when it comes to communication technology. Here are a few applications of electromagnetic waves in our lives. Radio waves: For communication uses, such as television communication and radio. Microwaves: Used in a microwave oven to heat meals, and for satellite television. The visible light This is the portion of the electromagnetic spectrum that helps us to see all the objects, including the colors. Ultra-violet: Ultraviolet waves can cause many chemical reactions. X-rays: X-rays are used as a diagnostic tool in medicine and as a treatment for certain forms of cancer. Useful for detecting injuries, monitoring recovery, and so on. Because X-rays damage living tissues, care must be taken to avoid over exposure. Gamma rays: These rays are used in cancer radiation therapy to kill off cancer cells. 7 The Use of Electromagnetic Radiation in the Physiotherapy Physical modalities such as shortwave diathermy (SWD) and microwave diathermy (MWD), the infrared (IR), and ultraviolet (UV) are all classified as portions of the electromagnetic spectrum according to corresponding wavelengths & frequencies associated with each region can be used as methods of physiotherapy suitable for treatment of different types of diseases. Effects of Electromagnetic Waves on Cells and Tissue  Exposure to some types of electromagnetic radiation primarily causes heating effects. However, over-exposure may result in harmful effects such as pain of sunburn or skin cancer.  Electromagnetic waves can be classified as either ionizing radiation or non-ionizing radiation: Ionizing radiations Ionizing radiation are extremely high frequency electromagnetic waves, which include X-rays and gamma rays. Ionizing radiation can inhibit cell division and is therefore used in very small doses for imaging, or in larger doses to destroy tissue for the treatment of cancer. Non-ionizing radiations Non-ionizing radiation are waves with lower frequency, longer wavelength and lower energy. Examples are ultra-violet, infrared radiation, short waves and microwave. 8