A Brief Guide to Electromagnetic Waves | Electromagnetism — Transcript

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1. 0:05For humans, the entire universe could not function without light.
2. 0:09We see and understand things because of light. Without it, our eyes cannot see objects.
3. 0:15In fact, we humans couldn't survive without the sun's light.
4. 0:19Light plays a crucial role in understanding the structure and properties of everything from atoms to the universe.
5. 0:26This light raises many questions for humanity.
6. 0:29Since ancient times, we have been trying to understand what light is.
7. 0:35Light acts like a messenger of information.
8. 0:38When it encounters an object, it reflects off that object carrying information from it then enters our eyes.
9. 0:46Within a millionth of a second, our brain processes this information and helps us understand what we are seeing.
10. 0:52Even though light is a messenger of information, it is itself invisible.
11. 0:58That's why space appears so dark. We can only see the existence of light when it encounters an object.
12. 1:04We see rays of sunlight because they pass through dust or gases.
13. 1:10We already know that light travels at the incredible speed of around 300000 km/s, and doesn't require any medium to travel.
14. 1:18This is the maximum speed of our universe. It is a very special and unique property of light.
15. 1:25Nothing else can travel at this speed.
16. 1:27However, one of the greatest physicists of the nineteenth century who worked on electricity and magnetism,
17. 1:32predicted through his equations that light is just a part of radiation.
18. 1:37Along with light, all radiation travels at the same speed.
19. 1:40This radiation is called electromagnetic radiation, or electromagnetic waves.
20. 1:56Every charge particle in our universe has an electric field.
21. 2:00An electric field is simply a distribution of force, or lines of force.
22. 2:05Electric field Lines are the simplest way to understand an electric field.
23. 2:10First introduced by the father of electricity, michael Faraday.
24. 2:14Electrons have a negative charge, so they have an electric field,
25. 2:18while protons have a positive charge, and also have an electric field.
26. 2:23However, the fields differ depending on the charge.
27. 2:26For a positive point charge, the electric field lines radiate outward,
28. 2:30while for negatively charged, the electric field lines radiate inward.
29. 2:35Simply put, the electric field originates at a positive charge and terminates at a negative charge.
30. 2:41In the case of an isolated positive point charge, the electric field line starts at the charge and extends to infinity.
31. 2:48For an isolated negative point charge, the electric field lines start at infinity and end at the negative charge.
32. 2:55So this field exists around the charge at all times, even if there are no other charge particles nearby.
33. 3:02Although the range of an electric field may be infinite, the strength decreases with distance,
34. 3:08meaning the field is stronger near the charge.
35. 3:11The electric field is responsible for electric force, where, like same charges repel each other and opposite charges attract.
36. 3:19The field is always active. When two opposite charges come close together,
37. 3:23the electric field of the positive charge links with the electric field of the negative charge.
38. 3:29When two positive charges come close together, due to their similar outward fields, they repel each other.
39. 3:37Magnetic forces were first observed in natural magnets.
40. 3:41Similar to electric fields, Magnets also have a field called a magnetic field.
41. 3:46A magnet always has two poles, a north pole and a south pole.
42. 3:50Magnetic field lines always start at the north pole and end of the south pole of the magnet.
43. 3:57Like electric charges, similar magnetic poles repel each other, while opposite poles attract.
44. 4:06The main difference between electric and magnetic fields is that,
45. 4:09in nature, negative and positive charges can occur independently of one another.
46. 4:14Whereas magnets always have two opposite poles.
47. 4:18We have never found independent magnetic poles in nature with only north pole or only south pole.
48. 4:24Even if a magnet is cut into two pieces, each piece becomes a new magnet with both a north and south Pole.
49. 4:31No matter how many times we cut it, the pieces always have opposite poles.
50. 4:48Our universe operates with four fundamental forces,
51. 4:51the strong force, the weak force, gravitational force, and electromagnetic force.
52. 4:57Electromagnetic force is a combination of electric force and magnetic force.
53. 5:02But why do we combine them? Why can't they be separate forces?
54. 5:07The story of electromagnetism begins with the invention of the battery.
55. 5:12In 18 hundred Alessandro Volta invented the battery, a device that pushes electrons from one place to another.
56. 5:19This movement of electrons is known as electricity.
57. 5:23An electron is a charge particle, so when a charge particle moves, it creates electricity.
58. 5:29In 1820, danish physicist Hans Christian over Steed conducted a famous experiment.
59. 5:36He placed a compass near a current carrying wire.
60. 5:39Naturally, a compass needle points in the direction of north and south Pole, direction of Earth.
61. 5:45But when he placed near the current carrying wire, the needle deflected from its original direction.
62. 5:51This demonstrated that the movement of charges produces magnetic effects,
63. 5:56which is why the compass needle was deflected.
64. 5:59However, a stationary charge, no matter how large, has no effect on a magnetic needle,
65. 6:04a charge must be moving in order to create a magnetic field.
66. 6:09When charge particles move in a straight line, they produce magnetic fields around them.
67. 6:14For charges moving in the opposite direction, the magnetic field will also be opposite.
68. 6:19This can be easily explained by the right hand rule.
69. 6:22Point your right hand thumb along the flow of current. Then curl your fingers as if wrapping around the wire.
70. 6:28The direction your fingers point is the direction of the magnetic field created by the current.
71. 6:37The 19’th century was an incredible period for new inventions.
72. 6:41At that time, the only source of electricity was the battery, but the demand for electricity was enormous.
73. 6:48Scientists had to find a way to produce electricity other than by using batteries.
74. 6:53Faraday worked on this problem. He asked himself If electricity could produce magnetism.
75. 6:59Why couldn't magnetism produce electricity? After years of work, he succeeded in 1831.
76. 7:06When a coil of wire is connected to a current meter and a magnet is moved inside the coil,
77. 7:11The needle on the meter deflects.
78. 7:14When a magnet moves forward, electrons start moving.
79. 7:17When the magnet moves backward, electrons start moving in the opposite direction.
80. 7:22A changing magnetic field causes electrons to move in different directions.
81. 7:26If we place a light bulb, we can see that the bulb starts glowing because the moving electrons create electricity.
82. 7:33This indicates that a changing magnetic field produces a changing electric field.
83. 7:39With this discovery, we later created generators which are used to produce electricity.
84. 7:44Generators are simple. When we rotate, a magnet changes in its direction produce electricity.
85. 7:52Thus a charge will produce a magnetic field, but only if it's moving.
86. 7:57A magnetic field will produce a current, but only if it's changing.
87. 8:03A moving charge produces a magnetic field. But what happens if the moving charge suddenly changes direction?
88. 8:10This phenomenon was explained very well by one of the greatest physicist mathematicians.
89. 8:27Faraday's ideas on electricity and magnetism were put into mathematical form by physicist James Clerk Maxwell.
90. 8:35He formulated four beautiful equations on electricity and magnetism.
91. 8:39For easy understanding let's review these formulas in simple terms.
92. 8:44His first equation is about electricity.
93. 8:46It states that electric charges, whether positive or negative, create an electric field.
94. 8:53The second equation is about magnetism.
95. 8:56All magnets have two poles.
96. 8:58The magnetic field starts at one pole and ends at the other, therefore magnetic charges cancel each other out.
97. 9:05This means there are no magnets that exist with only one pole.
98. 9:09Magnets always have two poles, and their magnetic charges cancel each other out.
99. 9:15The third equation explains that a charge in motion produces a magnetic field,
100. 9:21and a changing magnetic field induces a changing electric field.
101. 9:25These first three equations are relatively straightforward, and we already have some understanding of them.
102. 9:32Now we move on to the next step. What happens when a charge accelerates?
103. 9:37Acceleration means an object changes its speed or direction.
104. 9:40A charged particle can vibrate, which means it continuously changes direction.
105. 9:46And vibration implies acceleration. Let's observe the vibration in slow motion.
106. 9:51First, the charge moves upward, creating a clockwise magnetic field around the charge.
107. 9:57Then the charge moves downward, creating a counter clockwise magnetic field.
108. 10:02This happens very quickly. So the magnetic field around the charge also changes rapidly.
109. 10:09Now it becomes clear. we already know that changing magnetic fields can induce changing electric fields.
110. 10:16So as the charge vibrates, the changing electric field induces a changing magnetic field.
111. 10:22And the changing magnetic field induces a changing electric field.
112. 10:26This process repeats continuously propagating through space.
113. 10:31The electric and magnetic fields work together to push each other along.
114. 10:35This field. Conversion is called electromagnetic waves.
115. 10:39At any point, the electric and magnetic fields are perpendicular to one another and to the direction of propagation.
116. 10:48This is the fourth equation of Maxwell. Electromagnetic waves are produced whenever a charge is an accelerated motion.
117. 10:55These waves don't require any medium to travel. They can propagate through a vacuum.
118. 11:01If the charge stops vibrating, new electromagnetic waves won't be produced,
119. 11:06but the waves already created will continue to spread.
120. 11:10From his equation, maxwell calculated that electromagnetic waves propagate through space
121. 11:15at a constant speed of 300000 km/s and never slow down or stop.
122. 11:22He realized the speed is very close to something familiar to us, The SPEED OF LIGHT.
123. 11:28This led him to conclude that light itself is an electromagnetic wave.
124. 11:34However, the existence of electromagnetic waves was only a mathematical prediction by Maxwell,
125. 11:41But in 1888, german physicist Heinrich Hertz produced electromagnetic waves in his laboratory
126. 11:48and proved that their speed is 300000 km/s in a vacuum.
127. 11:53This was the first experimental proof of electromagnetic waves.
128. 11:59We know that accelerating charges produce electromagnetic waves, but why do charge particles accelerate?
129. 12:06And how can light and electromagnetic waves be the same? To answer this, we need to understand the basic nature of waves.
130. 12:25Like ocean waves, Electromagnetic waves have crests and troughs.
131. 12:31The crest is the highest point of the wave, and the trough is the lowest point.
132. 12:35The center between the lowest and highest points is called the ‘mean position’.
133. 12:40The distance from the mean position to the crest or trough is called the amplitude.
134. 12:45This is the height of the wave. An amplitude is measured in meters.
135. 12:49The distance between two consecutive crests or troughs is called the ‘Wavelength’, which is also measured in meters.
136. 12:56Its symbol is lambda. A crest and a trough together make up one wave cycle.
137. 13:02If one wave cycle passes through a point in 1 second; the time period is 1 second or 1 Hertz.
138. 13:09If 10 wave cycles pass through a given point in 1second, then it's 10 Hertz, which is called the ‘Frequency’.
139. 13:17The number of wave cycles passing a particular point in 1 second is its frequency.
140. 13:25Consider three electromagnetic waves traveling at the same speed.
141. 13:29Since the speed of these 3 waves is the same, the number of wave cycles crossing a point per second would vary.
142. 13:36E.g., If the first wave cycle is long, fewer wave cycles will pass per second compared to the other two waves.
143. 13:44So the first wave has a low frequency, while the third wave has a higher frequency.
144. 13:50This means that a longer wavelength has a lower frequency and a shorter wavelength has a higher frequency.
145. 13:57The frequency of a wave is inversely proportional to its wavelength.
146. 14:02But how do electromagnetic waves have different wavelengths and frequencies?
147. 14:09We know that electromagnetic waves are produced by the acceleration of charged particles.
148. 14:15But not all charges accelerate or vibrate at the same rate.
149. 14:19If a charge vibrates slightly, it produces lower frequency electromagnetic waves.
150. 14:24If a charge accelerates rapidly, it produces higher frequency electromagnetic waves.
151. 14:30So the intensity of vibration determines the frequency of an electromagnetic wave.
152. 14:37The basic principle of electromagnetic waves is
153. 14:40that their speed in a vacuum is equal to their wavelength, multiplied by their frequency.
154. 14:46If we multiply any given electromagnetic wave’s wavelength and frequency, we get the speed of light.
155. 14:53The speed of light never changes.
156. 14:55If we want to find the wavelength of an electromagnetic wave with a frequency of 900000 Hz, we just need to use this formula.
157. 15:05So wavelength equals the speed of light, divided by the frequency.
158. 15:10In this case, we would find that the wavelength is 330 m.
159. 15:15The wavelength and frequency are directly related to each other.
160. 15:20All electromagnetic waves carry energy, and the amount of energy depends on their frequency and amplitude.
161. 15:27The higher the frequency — the more energy ; The lower the frequency — the less energy.
162. 15:34Electromagnetic waves come in different wavelengths, frequencies and energies.
163. 15:40So we classify them into different categories.
164. 15:56We already know that the distance between two consecutive crests is called the wavelength.
165. 16:01The longest electromagnetic waves are 100000 km long with a frequency as low as 3 Hertz..
166. 16:09Electromagnetic waves can theoretically have wavelengths as long as 1 billion km.
167. 16:15But such wavelengths are undetectable, because their frequency is less than 1 Hertz.
168. 16:21Even at a speed of 300000 km/s, such a wave wouldn't compete one cycle per second, so the energy becomes undetectable.
169. 16:32The shortest electromagnetic waves have a wavelength of 10^-12 meters, or even smaller,
170. 16:41With a frequency of 10^24 Hz or more.
171. 16:45Based on wavelength and frequency, we categorize electromagnetic waves into different groups.
172. 16:51Radio waves, microwaves, infrared, visible light, ultra violet, X rays, and gamma rays.
173. 17:00The most extreme waves are Gamma rays, which have extremely high frequency and energy.
174. 17:06Depending on their frequency, their energy varies.
175. 17:09The human eye can detect only a certain range of electromagnetic waves ——
176. 17:14Between wavelengths of 380 nm and 760 nm, which we call ‘Visible light’.
177. 17:30Since visible light is familiar to us, we will start with this group.
178. 17:35Unlike other groups, it's very special because we see things and understand the universe through visible light.
179. 17:42To understand visible light, we need to look into bore's model of the atom.
180. 17:47Electrons orbit the nucleus and different energy levels. And these energy levels vary by atom.
181. 17:54Energy is measured in Electron volts. For a hydrogen atom. The first shell's electron has -13.6 eV.
182. 18:02The second shell has -3.4, the third shell -1.5 and so on.
183. 18:08The energy of electrons and atoms is quantized, meaning that the energy of the first shell is fixed at -13.6 eV.
184. 18:17It cannot be -13.7 or -13.5. This is the same for all hydrogen atoms in the universe.
185. 18:27In nature, electrons orbit in their ground state, but when they gain energy, they jump to a higher energy level.
186. 18:35E.G., imagine an electron in a hydrogen atom gains some energy, and it jumps from the second orbit to the third orbit.
187. 18:44The electron in the second orbit has -3.4 eV and in the third orbit it has -1.5 eV.
188. 18:52This means the electron gained 1.9 eV of energy. That's why it jumped from the second to the third orbit.
189. 19:00As we have seen before, electrons always prefer to be in the lowest available orbit, so they eventually return to a lower orbit.
190. 19:09Return means it undergoes acceleration and its velocity changes.
191. 19:13When a charge is accelerated, it emits electromagnetic radiation.
192. 19:19We know that the wavelength, frequency, and energy of electromagnetic waves
193. 19:24depend on the rate of acceleration or vibration of the charge.
194. 19:29When an electron moves from the third orbit back to the second orbit, it emits an electromagnetic wave with an energy of 1.9 eV.
195. 19:38This energy packet is called a photon.
196. 19:41Electromagnetic waves and photons are the same. Particle nature of Electromagnetic waves are photons.
197. 19:49There is a formula for converting energy into wavelength.
198. 19:52And in this case, we find that the electromagnetic wave has a wavelength of 654 nm.
199. 19:59The visible light range starts from a wavelength of 760 nm to 380 nm, which we call the visible light spectrum.
200. 20:09A wavelength of 654 nm corresponds to red light.
201. 20:15In the visible light spectrum, red light has the longest wavelength, while violet has the shortest wavelength,
202. 20:22the energy range for visible light from red to violet is 1.63 eV to 3.26 eV.
203. 20:31Any energy released within this range is visible light.
204. 20:36If an electron in a hydrogen atom jumps from the fourth orbit to the second orbit,
205. 20:42it emits electromagnetic waves with an energy of 2.55 eV, corresponding to a wavelength of 488 nm, which is green.
206. 20:54Thus, we have red light, green light, blue light, violet light, and many others.
207. 21:00They differ only in wavelength, frequency or energy. The perception of color that something happens in our minds.
208. 21:08White light consists of all color wavelengths, but when it strikes an object,
209. 21:13most of the color wavelengths are absorbed by the objects atoms, leaving only red light to be emitted.
210. 21:20That's why red objects appear red.
211. 21:24A wavelength of 654 nm is emitted by just one hydrogen atom at a time,
212. 21:30but the Sun contains 10^57 hydrogen atoms.
213. 21:35Due to the extreme pressure of the sun's inner core, atoms heat up and gain varying amounts of energy,
214. 21:41causing electrons to jump between different energy levels.
215. 21:44Depending on the distance of their jumps, they emit electromagnetic waves of different wavelengths.
216. 21:51Electromagnetic waves are not only emitted by the sun's inner atoms.
217. 21:55In the sun's plasma, countless free electrons vibrate randomly, also emitting electromagnetic waves of various wavelengths.
218. 22:03Plasma refers to the part of the Sun where unpaired electrons and nuclei exist.
219. 22:09Moreover, there are trillions of stars in the universe all emitting electromagnetic radiation.
220. 22:16All high temperature objects emit visible light, electromagnetic waves.
221. 22:21Humans also emit electromagnetic radiation, but not in the visible light range.
222. 22:39Infrared radiation lies just beyond red visible light, with wavelengths between 760 nm and 1000000 nm, or 1 mm.
223. 22:50When an object is not quite hot enough to radiate visible light, it emits most of its energy in the infrared range.
224. 22:57Infrared radiation has an energy range of 0.0012 eV to 1.65 eV,
225. 23:06Eg., if a molecule releases 1 eV of energy, its wavelength is 1240 nm, which falls in the infrared range.
226. 23:19Infrared radiation is produced by the vibration and collisions of molecules within an object.
227. 23:25You might wonder how neutral molecules, which have no charge, can produce electromagnetic waves.
228. 23:33Take the carbon dioxide molecule as an example. It consists of one carbon atom and two oxygen atoms.
229. 23:39Carbon has 6 electrons and oxygen has 8 electrons.
230. 23:43So the molecule has 22 protons and 22 electrons, making it electrically neutral.
231. 23:49However, the electron distribution is uneven. The atom with more electrons pulls the atom with fewer electrons.
232. 23:58So in this case, the oxygen atom pulls the carbon atom more strongly, creating an electrical imbalance between atoms.
233. 24:06The atom with more electrons becomes a negative pole, while the atom with fewer electrons becomes a positive pole.
234. 24:13Even though the overall molecule is neutral, It has two electrical poles and is called a Dipole molecule.
235. 24:20When the charge oscillates, it produces electromagnetic waves.
236. 24:24During molecular vibration, these charge poles stretch or vibrate, producing electromagnetic waves.
237. 24:32The frequency of electromagnetic waves depends on the frequency of molecular vibration or rotation.
238. 24:42Each molecule has a different range of vibration modes.
239. 24:45For instance, when carbon dioxide absorbs the right amount of energy for vibration,
240. 24:50it produces a wavelength of around a 1000 nanometers.
241. 24:53Thus, carbon dioxide can absorb or emit electromagnetic waves with a wavelength of around a 1000 nanometers.
242. 25:01Heat causes molecules to vibrate, since heat is the primary source of infrared radiation,
243. 25:08Any object with the temperature emits infrared radiation. Even objects we think of as cold, such as ice, emit infrared radiation.
244. 25:17In fact, an object with a temperature above absolute zero emits radiation.
245. 25:22Absolute zero temperature is -273 degrees Celsius, and achieving absolute zero is physically impossible.
246. 25:31Our average body temperature is 37 degrees Celsius.
247. 25:35So we constantly emit electromagnetic waves with wavelengths of around 10000 nm, which are infrared.
248. 25:45As we can see, the wavelength of electromagnetic waves depends on how hot objects are.
249. 25:51As heat decreases, the intensity of electromagnetic radiation decreases, causing the wavelength to increase.
250. 25:59Hotter objects release shorter wavelengths because their atoms vibrate more rapidly,
251. 26:04while cooler objects release longer wavelengths.
252. 26:09Since infrared lies beyond the visible light spectrum, we cannot see it, but some animals, such as snakes and frogs, can detect.
253. 26:17Even though we cannot see infrared radiation, we can feel it as heat.
254. 26:22However, we have managed to create infrared cameras that help us see infrared radiation, which is useful in many industries.
255. 26:30At night, when there is no visible light, all objects on Earth become dark, but they still emit infrared radiation.
256. 26:37With the help of infrared cameras, we can see objects in the ‘Dark’.
257. 26:52Microwaves have wavelengths longer than infrared waves, ranging between 1 mm and 1 m,
258. 26:59with corresponding energy ranges from 0.0012 to 0.0000012 eV.
259. 27:09We are most familiar with microwaves because they cook food rapidly.
260. 27:13Every food contains water molecules, and these water molecules can absorb specific ranges of EM waves.
261. 27:20In a microwave oven, there is a vacuum chamber with magnets and electrodes called a ‘Magnetron’
262. 27:27which produces a specific range of electromagnetic waves.
263. 27:31When these waves encounter water molecules, they cause the molecules to vibrate and rotate.
264. 27:37These vibrations, and the resulting friction between the molecules generate heat, cooking the food quickly.
265. 27:43In household microwave ovens, we typically use electromagnetic waves with wavelengths of 122 mm.
266. 27:51Microwaves are reflected by metals, but can easily pass through plastic or glass,
267. 27:57which is why we use plastic or glass containers to cook food in the microwave.
268. 28:03Microwaves are also used for long distance satellite communications,
269. 28:07radar systems for spacecraft navigation, and measuring the speed of vehicles.
270. 28:23In the electromagnetic spectrum, radio waves have the longest wavelengths and the lowest frequencies.
271. 28:30Their wavelengths range from 1 m to 100000 km, with frequencies ranging from 300 MHz to 3 Hz.
272. 28:381 MHz is equal to 1000000 Hz. At 300 MHz, the wavelength is 1 meter.
273. 28:45Due to their long wavelengths, radio waves are considered the safest form of non ionizing radiation,
274. 28:51since their wavelengths are long and their frequencies low, they have low energy.
275. 28:57The energy of radio waves ranges from 0.0000012 eV to 10^-14 eV.
276. 29:09Non ionizing radiation doesn't have enough energy to remove tightly bound electrons from atoms,
277. 29:16so it doesn't cause damage to the cellular structure of our bodies.
278. 29:19However, long term exposure to radio waves with higher frequencies can increase body temperature.
279. 29:27Radio waves are produced by charged particles when they accelerate.
280. 29:32We artificially produce radio waves more than any other type of electromagnetic wave
281. 29:37by moving electrons back and forth in a device called an ‘Antenna’.
282. 29:41Naturally, these waves are produced by lightning and astronomical objects such as galaxies and nebulas.
283. 29:50We have seen that electromagnetic waves with longer wavelengths than visible light,
284. 29:54have lower frequencies and energies, making them non ionizing radiation.
285. 29:59Thus they are safe for use in everyday life. Wavelengths from 700 nm to 100000 km, are considered non ionized radiation.
286. 30:09Non ionize radiation cannot break the atoms and molecules in living organisms.
287. 30:14However, electromagnetic waves with wavelengths shorter than visible light are extremely high in frequency and energy,
288. 30:21Making them very Harmful.
289. 30:35Ultraviolet radiation makes up about 10 % of the total electromagnetic radiation from the Sun.
290. 30:43UV wavelengths range from 400 nm to 10 nm, with energy levels between 3.1 and 12 eV
291. 30:53Like visible light, ultraviolet radiation is emitted by excited electrons,
292. 30:58For example, considered the Bohr’s model of a hydrogen atom.
293. 31:02The electron in the first orbit has -13.6 eV, and in the second orbit it has -3.4 eV.
294. 31:11If the electron gains enough energy, it can jump from the first to the second orbit.
295. 31:15When it returns to the first orbit, it emits 10.2 eV of energy, which corresponds to a wavelength of 122 nm.
296. 31:24Since ultraviolet waves fall between 400 and 10 nm in wavelength and between 3.1 and 12 eV of energy.
297. 31:33An electron returning from the second to the first orbit in a hydrogen atom releases ultraviolet radiation.
298. 31:40Similar to hydrogen atoms, mercury, helium and carbon atoms are also major sources of UV radiation.
299. 31:49Ultraviolet radiation is divided into three groups based on wavelength, frequency and energy.
300. 31:57UV-A that's 400 to 320 nm. UV-B, that's 320 to 280 nm, and UV-C that's 280 to 100 nanometers.
301. 32:08UVC is the most harmful form of UV radiation. But how exactly is it harmful to humans?
302. 32:16Our bodies function based on DNA, which instruct cells on how to work.
303. 32:22DNA consists of complex molecules. Molecules are made of atoms. And when UV radiation enters DNA molecules,
304. 32:29it causes electrons within the atoms to absorb energy and jump to higher energy states.
305. 32:35This sudden change in electron position can break the bonds between atoms in the molecule,
306. 32:41causing the structure of the molecule to collapse. This molecular collapse leads to damage DNA.
307. 32:47Since damaged DNA can no longer properly instruct cells, the result is malfunctioning cells.
308. 32:53This can lead to harmful conditions such as cancer, skin burns, eye damage, and a weakened immune system.
309. 33:02Fortunately, most UV radiation is absorbed by the ozone layer. The ozone layer contains ozone molecules,
310. 33:09and when UV radiation strikes these molecules, it breaks them apart into dioxygen (O2) and individual oxygen atoms.
311. 33:18This process absorbs the energy of the UV rays, preventing them from reaching earth's surface.
312. 33:23The individual oxygen atoms then recombine the di-oxygen to form ozone molecules again.
313. 33:30This continuous reforming cycle of ozone protects life on Earth from harmful ultraviolet radiation.
314. 33:47X rays have wavelengths shorter than ultra violet waves, ranging from 10 nm to 0.01 nm,
315. 33:55with equivalent energy levels between 12 eV and 120000 eV.
316. 34:03When high energy photons strike an atom, they can eject tightly bound electrons from the atoms inner shell,
317. 34:09ionizing the atom by causing it to lose an electron.
318. 34:13As we know, electrons always seek to fill the inner shell.
319. 34:16So when higher energy shell electrons fall into the inner shell, they release X rays.
320. 34:23X rays can also be produced when high energy negatively charged free electrons
321. 34:29pass near the positively charged nucleus of an atom.
322. 34:32as the electrons are deflected by the nucleus due to the attraction between opposite charges
323. 34:38This sudden change in direction emits a continuous X ray spectrum.
324. 34:42This process is called Bremsstrahlung radiation.
325. 34:49We produce X rays by sudden collision of high speed electrons.
326. 34:53Although X rays are more harmful than ultraviolet rays, we have developed ways to manage and use them safely.
327. 35:13Gamma rays are extremely high energy electromagnetic waves,
328. 35:17and their wavelengths are billions of times smaller than those of visible light.
329. 35:21Their wavelengths range from 0.01 nm to 10^-7 nm, and their energy levels range from 120000 eV to 10 million eV.
330. 35:35These are extremely high energy photons.
331. 35:39Gamma rays are produced during extreme cosmic events,
332. 35:42such as when a star dies and becomes a Neutron star or Black hole through a ‘Supernova explosion’.
333. 35:48These supernova explosions emit highly energetic electromagnetic waves.
334. 35:54Neutron stars have very strong magnetic fields,
335. 35:56and when charged particles become trapped in these fields, they accelerate to nearly the speed of light.
336. 36:02As a result, they emit high energy photons - Gamma rays.
337. 36:06Our sun also emits gamma rays ; In the sun's inner core, the process of nuclear fusion constantly takes place
338. 36:14when hydrogen atoms fuse to form helium, gamma rays are emitted.
339. 36:18These gamma rays travel from the inner core to the sun's atmosphere,
340. 36:22where they collide with atoms, gradually losing energy.
341. 36:25By the time they reach Earth, they have lost most of their energy and become non ionizing radiation.
342. 36:33Similarly, gamma rays are produced during nuclear fission.
343. 36:37When heavier nuclei split into two smaller nuclei, gamma radiation is emitted.
344. 36:42We have harnessed this process from nature to develop nuclear weapons.
345. 36:47If cosmic gamma rays were to directly enter our bodies, they would tear apart atoms and cause severe damage.
346. 36:54High energy electromagnetic waves are incredibly harmful to living organisms.
347. 36:58Fortunately, earth's atmosphere acts as a protective shield, blocking most of these cosmic threats.
348. 37:06However, while the atmosphere protects us from external cosmic dangers, humans have developed nuclear weapons
349. 37:12which could EXPLODE at any time due to POOR DECISIONS by world leaders.
350. 37:16Thus, the greatest threat to humanity may not come from the outside, but from humanity itself.