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Basic electrostatic questions

  1. Jun 16, 2012 #1
    hello folks,

    Actually i'm not an engineer, but i have a couple of questions regarding electricity and i hope i am posting this in the right forum :)

    1- when there's a charged object, that comes close to another object, a spark tends to happen between them, so that the charged body emptys the charge it holds.
    My questions is: what is the rule that governs the amount of charge required to generate this spark in respect to the distance between the 2 objects?

    2-I was looking for objects with high Relative permittivity and found a table on wikipedia telling that there are objects with an ε over 200,000. does this mean that, these objects cannot hold any charge practically?

    thanks guys :)
  2. jcsd
  3. Jun 16, 2012 #2

    My answer:

    1. spark is caused due to electric field breakdown. i.e. every material (such as air) has E-field strength. If E applied is more than this strength. The material breaksdown and material would act as conduct till the E-applied is short. Good example of it is lightning. You can read more about it from wiki.

    2. relative permittivity is used for dielectrics. Its technical definition has to do with polarization effects. If epsilon is high it means it can store more power. If you are familiar with capacitors. Power is capacitor is proportional to capacitance. Which in turn is proportional to electric permittivity of the dielectric. So, more the dielectric more energy it can store. Other property is that, more the permittivity of a material slower the propagation speed.

    Hope this helps.
  4. Jun 17, 2012 #3
    thanks for replying me.
    regarding the first question, i can understand the concept behind the generation of the spark itself, but i still cannot find a rule that can give me straight numbers for this.
    i mean lets assume a distance of 1 meter, between 2 point charges, with air or vaccum between them. what is the required amount of charge of each point in coulombs? (if u can show me a rule or something maybe?)

    ok now about the second question, i now understand that the higher ε the material has, it will store more energy, but i am looking for something different here:
    I want a material that can stop electrical attraction between 2 objects (isolation) without being charged, what material would do that best??

    thx :)
  5. Jun 18, 2012 #4
    So for each material there is e-field strength (in coulumbs) my EM textbook had this. As for the rule, you can use any rule to find the E-field between two objects. Most common is coulumbs law. This is all theoretical, practically this won't work because there is tiny bit of charge everywhere around you.

    I guess bit of incorrect explanation on my part here. So, basically high dielectric is insulator. and insulator prevents currents from interacting. The reason i confused myself and said it would store energy is because if insulator is placed between two conducting plates, the charges build up on plates. So, technically good insulator helps store charge (but this is in cap. only). So basically charge transfer between insulator is difficult and require lot of e-field. sry abt. confusion. insulator is day-to-day life is electric tape.

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