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## MCAT

### Course: MCAT>Unit 8

Lesson 10: Electrostatics

# Conservation of charge

The law of conservation of charge states that the total amount of electric charge in a closed system must remain constant. See how this law can be applied to various scenarios, such as when particles collide or decay. Learn how the law of conservation of charge can be used to deduce charges of unknown or undetected particles within a closed system. Created by David SantoPietro.

## Want to join the conversation?

• At , is an anti-electron (or positron) the same as a proton?
• Anti-particles have the same mass, but the opposite charge to their counter-particles. For example, the anti-electron (or positron) has +e charge and same mass as an electron. On the other hand, a proton has +e charge and is 1836 times heavier than the electron (or positron for that matter) .
• It is stated that if there is a neutral particle which breaks up into several charged particles, then the net charge should be 0. But Sal said that positive and negative are just used to describe two different charges. How can they cancel each other out then?

I also read in a book that because the net charge is zero when two differently charged particles with the same magnitude are placed together.This contradicts Sal's statement. Can someone kindly clear up the confusion?
• The convention of charges being called 'positive' and 'negative' has been made to make it easier for physicists to deal with charge, and thus this law has been stated in this way. Let me state it as such that it doesn't contradict with any convention being followed
There are two types of charge. The net total of the charge in existence, provided one type is the counterpart of the other, is constant.
• After , he said that a photon or a beam of light may turn into an electron and a positron. If a beam of light has no mass, how does it turn into particles that have (a very small amount of) mass?
• great question. I prefer to think about the process in reverse (as a first step in the discussion)
So...
If an electron meets with a positron what happens? and why? The positron is anti-matter and I find it useful to think about it as having the same amount of 'anti' mass as the electron has 'real' mass. So, when they meet, they annihilate one another.... their 'masses' are kind of cancelled out and converted into pure energy. (Good old 'E equals m c squared'...) This energy will now be in the form of radiation or photons.
Second part of the discussion: The reverse is also true...Photons can convert their energy into 'pairs' of particles. If the energy of the photon is high enough, then it might form an electron and a positron.
Can you work out what the wavelength of the original photon must be if it is going to have enough energy to produce electron-positron pair?
• I'm confused what exactly a Coulomb is and what it represents..
• Measure of how much charge there is.
Similar to kilograms for mass.
• Now I know charge is another property of matter, but it seems similar to energy. So is charge another form of energy?
• charge can be seen as an attractive or repulsive force between two particles while energy in laymans terms can be how fast something vibrates, like magnets attract each other fundamentally due to charges in them.
(1 vote)
• can the law of conservation of charge be stated as the total amount of charge within a space remains constant if kept under constant physical conditions?

are proton and anti-electron same?(in detail)
• The antimatter particle to the electron is the positron.
• Is it the flow of charge or the flow of electrons? I have seen both explanations for current.
• The direction of current is conventionally taken to be opposite to to the direction of flow of electrons.. I'd say flow of charge..
• Is the foundational concept of Conservation of Charge, paired with the Conservation of Energy, the basis for how the LHC detects new particles? Does it just basically look for missing total mass/charge/energy after a collision and see if the mystery particle proposed would fit that and then try to observe it?
• No - you can't just "look for missing total mass/charge/energy" that easily. Particles like the Higgs Boson will decay* into a set of lighter particles almost immediately. Those are detected and the physicists look for those specific sets.

(*) Particle decay means the particle (usually "Hadrons") spontaneously transforms into other particles. Of course, the conservation laws still apply.
• Do all the subatomic particles in universe have a charge if 1.6*10^-18 . If not then how is quantization of charge true ?