The Electromagnetic field, how Electric and Magnetic forces arise

[Music] welcome back to science click today the electromagnetic field imagine two people in the void of space playing catch with a ball when he throws the ball the first person experiences a recoil because he passes momentum onto the ball similarly when she receives it the other person absorbs the motion of the bull and also experiences recoil by throwing and catching the ball the two individuals have repelled each other they were motionless at first under now in motion if they continue to pass the ball their speeds will increase each time and they will move away from each other faster and faster they behave as if they were experiencing a force the action of the bull can be viewed as a force of repulsion [Music] in nature at the quantum scale this phenomenon is at work between certain particles such as electrons which constantly exchange virtual photons a virtual photon is a particle stemming from the laws of quantum physics which can appear out of nothing provided it disappears fast enough such that we cannot detect it a virtual Photon has a certain energy and the more energy it has the shorter its lifetime therefore the less energy a virtual Photon has the greater the distance it can travel by exchanging virtual photons electrons experience a repulsion a force that pushes them away from each other like the two people playing catch this force is increasingly powerful as the distance between electrons shortens because the virtual photons then have less distance to travel and can thus be more energetic many other particles exchange virtual photons and their tendency to interact in this way is called the electric charge [Music] the electron has an electric charge of -1e e is the basic unit for electric charge a particle will have a certain multiple of this Elementary brick some objects interact more than a single electron we can imagine an object containing two electrons and whose electric charge would be -2e moreover some particles like protons interact with virtual photons in the opposite way their electric charge is positive the charge of the proton for instance is Plus 1e just like with two electrons two positively charged particles repel each other however a negative particle and a positive particle attract each other charges of the same sign repel each other while opposite charges attract to take into account all these interactions we introduce the electric field we can conceive it as a sort of imaginary fabric if we place an electron in the field which is negatively charged the field turns blue however if we place a proton which is positively charged the field turns red if we drop new particles they will escape from the areas which have the same color as them a neutral particle without electric charge doesn't feel anything and moves in a straight line a positive charge such as a proton will be repelled by Red areas and attracted by Blue areas and a negative charge on the other hand will be attracted by red and repelled by Blue let's illustrate the electric field with several examples here is the field created by two electrons we see that the central position between the electrons is an equilibrium if we place a particle there it would remain motionless somewhat like a ball between two Hills now here is the field created by an electron and the proton the two particles attract each other as the electric field forms a bridge from one particle to the other finally if we place a chain of electrons on one side and a chain of protons on the other side we can create a uniform electric field in which a particle would always feel the same Force doing so we can make electrons move along an electric wire and thus create an electric current at this point a disturbing phenomenon comes into play consider an electric wire consisting of a long chain of protons and electrons through which flows an electric current which corresponds to the motion of electrons inside the wire imagine now that we leave an object a certain distance away from The Wire which carries a positive electric charge according to what we saw earlier each proton in The Wire repels the apple as their charges are both positive at the same time each electron attracts the apple with the same intensity overall if we add up all these forces they compensate each other and the apple does not experience any net force it remains Motionless let us now throw the Apple to the right [Music] strangely we now observe that it is gradually repelled by The Wire while it is not subject to an electric force the Apple seems to be experiencing a mysterious force that pushes it away this new force is very peculiar it does not appear when the apple is motionless but only when it is moving moreover it seems to depend on the direction and the speed of the Apple this mysterious Force which appears when an electric charge moves around is called the magnetic force to understand its origin we will have to review what special relativity teaches us before that though let's study the situation not from an outside point of view but rather as it is perceived by the Apple in its own frame of reference from this point of view it is not the Apple which moves to the right it is the wire that moves to the left now according to special relativity the faster an object moves the more its length gets contracted in the direction of motion in this reference frame the protons in The Wire are now in motion they will thus get contracted along the direction of the wire the protons come closer to each other conversely the electrons appear to be moving more slowly because the entire wire is now moving to the left they therefore get slightly stretched compared to the previous point of view and move away from each other overall when we add up the forces acting on the Apple from this point of view they no longer cancel out there are more positive charges protons than negative charges therefore the wire exerts a repulsive Force which pushes back the Apple by considering special relativity we see that the electric field of a charge gets distorted when it starts moving this phenomenon involves the appearance of a new Force the magnetic force which is in fact an electric force perceived from a different reference frame similarly to the electric field we can summarize all these behaviors under another field the magnetic field when an electric charge moves it creates a magnetic field around it which can be represented as arrows revolving around the direction of motion the magnetic force is a consequence of special relativity and the behavior of the magnetic field is therefore rather strange in a magnetic field a stationary particle does not feel any Force on the other hand a moving particle experiences a force whose strength depends on how perpendicularly the particle moves in relation to the magnetic field this Force tends to pull particles in circular trajectories the size of which depends on their Mass their speed the intensity of the field and the electric charge although it is difficult to visualize we can get some intuition of the magnetic field by considering the following experiment we wind a wire on itself to form a long coil and we apply an electric current to it by moving inside the wire each electron creates a small magnetic field around itself overall these small magnetic fields add up and form a large-scale field which loops around exiting at one end and entering back through the other end in this way the coil behaves like a magnet an object with Magnetic North and South Poles we call this an electromagnet as for electric charges poles of the same type repel each other while opposite poles attract in the center of the coil the magnetic field is somewhat uniform almost the same everywhere aligned with the axis of the coil if we were to launch an electron and a proton inside it the two particles would follow circular trajectories because of the field but in opposite directions since the electron is negative whereas the proton is positive in general most magnets do not require any electric current to operate some naturally have a magnetic field we call them permanent magnets in essence Elementary particles like electrons have a Quantum property called spin as a first approximation we can interpret spin as a sort of rotation of the particle on itself as it rotates the particle generates an electric current which as for the coil generates a magnetic field Elementary particles thus behave like very small magnets and if we align them in a material they can form magnetic substances [Music] to conclude the electric and magnetic fields are inseparable one is the origin of the other and it is natural to unite them under a single concept the electromagnetic field the electromagnetic field behaves and evolves in a well-defined way which can be summarized in four fundamental principles we call these Maxwell's equations the first equation tells us that an electric charge acts as a source for the electric field the second equation tells us that Standalone magnetic charges cannot exist objects which would only have a North Pole without a South Pole or vice versa a magnetic north pole always comes with a South Pole and if we try to cut a magnet in two we inevitably end up with two smaller magnets with two poles each the last two equations translate how the electric and magnetic fields evolve with respect to each other the first of these two equations tells us that a disturbance in the magnetic field affects the electric field if we push a magnet inside a coil of wire the magnetic field changes which disturbs the electric field and sets the electrons in motion in this way by shaking a magnet inside a coil we can produce an electric current this is called induction a change in magnetic field can induce an electric current running through a wire this technique is widely used by wind turbines nuclear power plants or even in telephones to convert motion into an electric signal finally the fourth equation tells us that an electric current or a change in the electric field leads to a disturbance of the magnetic field this last equation is crucial because with the previous one it brings about a circularity a change in the electric field disturbs the magnetic field and this disturbance of the magnetic field in turn disturbs the electric field this alternation between the electric and the magnetic fields allows electromagnetic energy to propagate in the form of waves which travel at the speed of virtual photons we speak of electromagnetic waves they include microwaves x-rays infrared or even light many fascinating experiments can be explained by the laws of electromagnetism one of these concerns how we can slow down gravity to do this simply drop a magnet over a coil of wire at first the magnet Falls faster and faster because it undergoes the attraction of the Earth but as it approaches the coil its motion causes a change in the magnetic field this change in the magnetic field sets the electrons within the wire in motion the fall of the magnet generates an electric current in the coil a coil with an electric current running through it generates a magnetic field like a magnet this new magnetic field slightly counteracts the motion of the falling magnet and slows down its full inside the coil the magnet Falls more slowly as if less affected by gravity [Music] [Music]

Channel: ScienceClic English

Views: 428,631

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Id: XoVW7CRR5JY

Length: 14min 43sec (883 seconds)

Published: Sat Nov 05 2022

Reddit Comments

[u/VastlyAlluring]

Every time I asked my professors at college why exactly the electric force (the movement of electrons) produces a magnetic force, none bothered at all to tell me anything and always told me to just accept it. This video finally made me understand how magnetism arises.