Electromagnetic Waves and the Wave Nature of Light Lesson 1 PDF

# Lesson 1: Electromagnetic Waves and the Wave Nature of Light ## Word Detect The listed terms are related to the concept of electromagnetic waves. You may go through the lesson and find out to which classification in the boxes will each of these terms belong to. Write each term in their respectiv...

# Lesson 1: Electromagnetic Waves and the Wave Nature of Light ## Word Detect The listed terms are related to the concept of electromagnetic waves. You may go through the lesson and find out to which classification in the boxes will each of these terms belong to. Write each term in their respective box. | **Electromagnetic Wave** | **Misconceptions** | |---|---| | needs medium | harmful waves | | ionizing radiation | travels in vacuum | | communication | spectroscopy | | microwaves | imaging | | | ultraviolet rays | | | gamma waves | | | speed of light | | | visible | ## Electromagnetic Wave ### Examples - Radio - Microwave - Infrared - Visible light - Ultraviolet - X-rays - Gamma rays ### Uses - Communication - Heating - Medical imaging - Sterilization - Remote sensing - Security - Research ## Electromagnetic Spectrum and it's Applications As mentioned in the previous grade levels, light is believed to have a dual nature-a particle and a wave. As a particle, light carries with it bundles of energy called photons. As these photons travel and interact with electric fields, electromagnetic radiation is produced. Light begins to exhibit its wavelike nature when it shows properties such as reflection, refraction, interference, diffraction, and polarization. However, to understand the wave nature of light, we must explore the electromagnetic waves further. In this lesson, you will learn more about the different types of electromagnetic waves (including visible light), their properties, and their applications. **Electromagnetic (EM) Waves** EM waves are transverse oscillating waves composed of electric and magnetic fields. EM waves travel in a vacuum at the speed of $3.0 \times 10^8$ m/s. EM waves can travel even without a medium (i.e., a vacuum). In an EM wave, the electric field is perpendicular to the magnetic field. $\lambda$ = Wavelength - **Big Idea:** Each type of wave in the EM spectrum has properties that account for its behavior. **EM Spectrum and Its Applications** EM waves are classified according to their frequencies. They are also described according to their wavelengths and energies. Figure 3.2 shows the EM spectrum, which shows the different types of EM waves. | **Radiation type** | **Wavelength (m)** | **Frequency (Hz)** | |---|---|---| | Radio | 103 | 104 | | Microwave | 10-2 | 108 | | Infrared | 10-5 | 1012 | | Visible | 0.5 x 10-6 | 1015 | | Ultraviolet | 10-8 | 1016 | | X-ray | 10-10 | 1018 | | Gamma ray | 10-12 | 1020 | ## Radio Waves Radio waves are the region in the EM spectrum with the longest wavelength and the lowest frequencies in the EM spectrum. Radio waves have wavelengths ranging from 1 cm to 1 km, with frequencies ranging from 30 gigahertz (GHz) to 300 kilohertz (kHz). Within this frequency range are different bands of waves. - **Extremely low frequency (ELF)** waves are radio waves with frequencies of less than 3 kHz and wavelengths that are greater than 100 km. They are naturally generated in the atmosphere. - **Very low frequency (VLF)** waves are radio waves with frequencies ranging from 3 to 30 kHz and wavelengths ranging from 10 to 100 km. This band is also called as the myriameter band. These waves are used for military communications with submarines because of their ability to penetrate saltwater up to certain depths. - **Low-frequency (LF)** waves are radio waves with frequencies ranging from 30 to 300 kHz and wavelengths ranging from 1 m to 10 km. These are used for long-distance communications. - **Medium-frequency (MF)** waves have frequencies that range from 300 kHz to 3 MHz and wavelengths ranging from 100 m to 1 km. They are commonly used for amplitude modulation (AM) broadcasting and air traffic control. - **High-frequency (HF)** waves have frequencies ranging from 3 to 30 MHz and wavelengths ranging from 10 to 100 m. These are used in international broadcasting stations. - **Very high frequency (VHF)** waves have frequencies ranging from 30 to 300 MHz and wavelengths ranging from 1 to 10 m. These are used in digital audio broadcasting and mobile radio systems. - **Ultra-high frequency (UHF)** waves have a frequency ranging from 300 MHz to 3 GHz and wavelengths ranging from 10 cm to 1 m. This frequency is commonly used in TV broadcasting, global positioning systems (GPS), wireless fidelity (Wi-Fi), and Bluetooth technologies. ## Microwaves Microwaves have frequencies higher than those of radio waves. Their frequencies range from 300 MHz to 300 GHz. Microwaves also have sub-bands with different wavelengths and uses, such as L, S, C, X, and K. The L-bands are used in our GPS. Other bands are used for active remote sensing and also for radio detection and ranging (RADAR) systems. Many Bluetooth and Wi-Fi connections also operate using microwaves. ## Infrared Infrared (IR) waves are found between microwaves and visible light. IR waves have frequencies ranging from $3 \times 10^{11}$ to $4 \times 10^{14}$ Hz. They are grouped into near, mid-, and far infrared regions. They are invisible to the unaided eye but can be detected in the form of heat. In 1800, William Herschel first recorded the thermal measurement at the far end of the red spectrum, hence the name infrared (from the prefix infra-, meaning "below"). Infrared is used in remote sensing. The remote controls of our TV sets use IR to send signals to change channels. IR is also used in thermal imaging. An object can be made visible using IR technology. ## Visible Light The only part of the EM spectrum that can be seen by the unaided eye is the visible light. Visible light has frequencies ranging from 400 to 700 nm. The different colors of light are caused by differences in their subwavelengths. Colors appear exactly as those seen in the rainbow: red, orange, yellow, green, blue, indigo, and violet. Visible light allows us to see different objects. The visible light spectrum, shown in figure 3.6, has various applications such as spectral imaging. When visible light is emitted, certain patterns of dark lines and colors appear. This is what you call spectral signatures, which help in identifying the structure and composition of substances and are widely used in scientific research. ## Ultraviolet (UV) Waves In 1801, John Ritter successfully proved the existence of energy beyond the violet spectra of the visible light, naming it ultraviolet (UV). UV radiation extends from the violet spectra of the visible light through X-rays. It has a wavelength ranging from 10 to 400 nm. Most of the UV radiation that we receive comes from the sun. The sun's UV is classified as UVA, UVB, and UVC radiation. UVA is the least harmful of the three forms of UV radiation, whereas UVC is the most harmful. UVC, however, is absorbed by the ozone layer. UVB radiation can cause sunburn because, unlike IR, it causes a chemical reaction on the human skin. This eventually causes the skin to burn or change its color. However, prolonged or too much exposure to UVB radiation can cause cellular damage in an organism. It may cause the production of free radicals in the body or even DNA damage. ## X-rays X-rays were first observed and documented by Wilhelm Conrad Roentgen in 1895. The X-ray region is between the UV and the gamma regions. Their wavelengths are so small, which is why the energies carried in the X-ray and the gamma-ray regions are described in electron volts (eV). The EM spectrum is arranged in increasing frequencies and energies. The higher the frequency, the higher the energy carried by the wave. X-rays carry 100 eV to 200 keV of energy. X-rays can be classified as soft X-rays and hard X-rays. ## Gamma Rays Gamma rays are found at the end of the EM spectrum. Gamma rays contain the highest energy of all, possessing a range from 200 keV to about 200 MeV. Gamma rays are produced by objects with very high energy. Naturally, it can be produced by pulsars, supernova explosions, neutron stars, and also by the decay of some radioactive elements. ## Effects of EM Waves on Organisms With proper use, radiation can give us benefits. The waves of the electromagnetic spectrum, along with their varying energies, have various effects on organisms. Waves can be either non-ionizing or ionizing. Waves that have non-ionizing radiation include microwaves, radio waves, IR, visible light, and UV. On the other hand, waves with ionizing radiation include X-rays and gamma rays. Higher frequencies of UV rays are also ionizing, as shown in figure 3.9. | **Radiation type** | **Non-ionizing Radiation** | **Ionizing Radiation** | |---|---|---| | Radio | | | | Wavelength (m) | 103 | | | Microwave | | | | Wavelength (m) | 10-2 | | | Infrared | | | | Wavelength (m) | 10-5 | | | Visible | | | | Wavelength (m) | 0.5 x 10-6 | | | Ultraviolet| | | | Wavelength (m) | 10-8 | | | X-ray | | | | Wavelength (m) | 10-10| | | Gamma ray | | | | Wavelength (m) | 10-12 | | | **Frequency (Hz)** | **Non-ionizing Radiation** | **Ionizing Radiation** | |---|---|---| | **Radio** | 104 | | | **Microwave** | 108 | | | **Infrared** | 1012 | | | **Visible** | 1015 | | | **Ultraviolet** | 1016 | 1016 | | **X-ray** | | 1018 | | **Gamma Ray** | | 1020 | Radiation has different effects because it interacts differently with various materials. Waves with non-ionizing radiation cannot penetrate the cells of organisms, whereas waves with ionizing radiation are those that can penetrate the cells of organisms. Some waves with non-ionizing radiation, such as microwaves, effectively produce electric current and heat. This property makes microwaves very useful. You commonly use the heating ability of microwaves in cooking. However, these types of waves also have negative effects. Exposure to waves with non-ionizing radiation may cause photochemical reactions such as sunburn and thermal heating of surfaces. Exposure to these waves may have the same effects as that of electric current and heat. However, one should take note of the time of exposure, the distance to the source, and the kind of protection used. Objects with non-ionizing radiation may still affect organisms, as when they are intentionally or accidentally ingested. High-frequency ionizing radiation, on the other hand, can cause biological damage. Generally, these types of radiation affect fast-growing cells such as that of the hair and the skin. When ionizing radiation hits the cells, it may cause the cells to die, or to have cellular mutations. These mutated cells bring about changes to the organism. Some calculated mutations bring good effects, whereas others do not. Cancer cells are examples of mutated cells. The effects of radiation depend on how much time a person was exposed to it, the distance from the source, and the kind of protection or shield used. The closer a person is to the source of radiation, the greater is the risk of exposure. Also, the longer the time of exposure, the higher the risk on the person, as the amount of radiation may accumulate in the body. Proper protection should also be taken into account. In medical exposures, the room is usually built with materials such as lead to shield the body from harmful gamma rays. ## Acute and Chronic Exposure Acute exposure happens when you get high amounts of radiation exposure over a very short period of time, such as a person undergoing cancer treatment. Another kind of exposure is called chronic exposure. This occurs when a person is exposed to a small amount of radiation over a long period of time. People are also exposed to background radiation. Radiation from natural sources such as Earth materials and the food we eat contribute to the total background radiation. ## Measuring Radiation Radiation is measured using several units. To measure radioactivity, we use curie (Ci) or becquerel (Bq). For radiation exposure or the amount of radiation in air, we use roentgen (R) or coulomb per kilogram (C/kg). For absorbed doses or the amount of radiation absorbed by an object, we use radiation absorbed dose (rad) or gray (Gy). Last, for the dose equivalent or the totality of the amount of radiation actually absorbed (along with its medical effects), we use roentgen equivalent man (rem) or sievert (Sv). The International Atomic Energy Association (IAEA) has provided the standard dose limits for radiation exposure, as shown in table 3.1. | **Age** | **Occupational Exposure of Workers over the Age of 18** | **Occupational Exposure of Apprentices or Students (On-the-job Trainees) Ages 16-18** | |---|---|---| | **Effective dose per year (millisievert or mSv)** | 20 (average) 50 (in any single year)* | 6 | | **Equivalent dose per year (mSv)** | 20 (to the eye lens) 50 (in any single year) 500 (to the hands and feet, or to the skin) | 20 (to the eye lens) 150 (to the hands and feet, or to the skin) | *Some countries limit exposure to 20 mSv per year. *Additional restrictions apply to pregnant or breastfeeding females.