184_notes:charge_and_matter

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184_notes:charge_and_matter [2021/01/24 23:48] – bartonmo184_notes:charge_and_matter [2021/01/25 00:02] – bartonmo
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 [{{ 184_notes:atom_w_cloud.png?200|Electron cloud around positive nucleus }}] [{{ 184_notes:atom_w_cloud.png?200|Electron cloud around positive nucleus }}]
  
-**Most matter is neutral**, which means that the net charge (or sum of all the charges) of most atoms is zero. Since the charge of a proton is $+1.602 \cdot 10^{-19} \text{ C}$ and the charge of an electron is $-1.602 \cdot 10^{-19} \text{ C}$ (and the charge of a neutron is $0 \text{ C}$), this tells us that the number of protons in a neutral atom has to equal the number of electrons. //__Notice that if an object is neutral, it does not mean that the object has zero charge. It means that the amount of positive charge in the atom is equal to the amount of negative charge in the atom, so the **net** charge is zero.__//  +**Most matter is neutral, which means that the net charge (or sum of all the charges) of most atoms is zero.** Since the charge of a proton is $+1.602 \cdot 10^{-19} \text{ C}$ and the charge of an electron is $-1.602 \cdot 10^{-19} \text{ C}$ (and the charge of a neutron is $0 \text{ C}$), this tells us that the number of protons in a neutral atom has to equal the number of electrons. //__Notice that if an object is neutral, it does not mean that the object has zero charge. It means that the amount of positive charge in the atom is equal to the amount of negative charge in the atom, so the **net** charge is zero.__//  
  
 **If an object is //charged//, this means that the net charge of the object is no longer zero**. If the object has a negative net charge, this means that the object has an excess of electrons. If an object has a positive net charge, this means that the object is missing electrons. In theory you could also get a negative net charge by removing protons (or a positive charge by adding protons); however, protons are extremely difficult to remove (or add) because they are held together in the nucleus by the [[https://en.wikipedia.org/wiki/Strong_interaction|strong interaction]]. Since electrons are relatively easy to remove compared to a proton, almost all charged objects that you will encounter will be due to electrons being added or removed. **If an object is //charged//, this means that the net charge of the object is no longer zero**. If the object has a negative net charge, this means that the object has an excess of electrons. If an object has a positive net charge, this means that the object is missing electrons. In theory you could also get a negative net charge by removing protons (or a positive charge by adding protons); however, protons are extremely difficult to remove (or add) because they are held together in the nucleus by the [[https://en.wikipedia.org/wiki/Strong_interaction|strong interaction]]. Since electrons are relatively easy to remove compared to a proton, almost all charged objects that you will encounter will be due to electrons being added or removed.
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 If we start with a neutral atom by itself, we know that there will be a positive nucleus with a negative, circular electron cloud around it. The electron cloud is circular (spherical in 3D) because it is equally likely that the electrons are anywhere around the nucleus (shown in Figure 2a/3a).  If we start with a neutral atom by itself, we know that there will be a positive nucleus with a negative, circular electron cloud around it. The electron cloud is circular (spherical in 3D) because it is equally likely that the electrons are anywhere around the nucleus (shown in Figure 2a/3a). 
  
-**What would change about our atom if we put a charge next to a neutral atom?** +//What would change about our atom if we put a charge next to a neutral atom?//
  
 The electrons cannot leave their nucleus (unless [[https://en.wikipedia.org/wiki/Ionization|the interaction is very strong]]), but they are attracted to the positive charge. With a positive charge nearby, it is now more likely that the electrons will be on the left side of nucleus compared to the right (shown in Figure 2b), shifting the electron cloud toward the positive charge. Often, we will simplify this drawing to be just an oval that indicates which side of the atom is more positive and which side is more negative (shown in Figure 2c).   The electrons cannot leave their nucleus (unless [[https://en.wikipedia.org/wiki/Ionization|the interaction is very strong]]), but they are attracted to the positive charge. With a positive charge nearby, it is now more likely that the electrons will be on the left side of nucleus compared to the right (shown in Figure 2b), shifting the electron cloud toward the positive charge. Often, we will simplify this drawing to be just an oval that indicates which side of the atom is more positive and which side is more negative (shown in Figure 2c).  
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 === Insulators === === Insulators ===
-An insulator is an object or material where the electrons are tightly bound to the nucleus. This means that the electrons in an insulator can only move very small amounts and must stay close to their nuclei. //**Charges cannot move freely through an insulator.**// Common insulators include: plastic, glass, rubber, paper, wood, etc. +An insulator is an object or material where the electrons are tightly bound to the nucleus. This means that the electrons in an insulator can only move very small amounts and must stay close to their nuclei. **Charges cannot move freely through an insulator.** Common insulators include: plastic, glass, rubber, paper, wood, etc. 
  
 [{{  184_notes:insulatorpos.png?150|Charge distribution in an insulator from a positive charge}}] [{{  184_notes:insulatorpos.png?150|Charge distribution in an insulator from a positive charge}}]
  • 184_notes/charge_and_matter.txt
  • Last modified: 2021/01/25 00:06
  • by bartonmo