Can someone please explain to me how grounding works and what they MCAT would want me to know about it?
What is grounding?
- Thread starter kfcman289
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If you are talking about electrical "grounding,' that is a safety feature for AC electrical equipment, and its purpose is to prevent electrical shock to the users of such equipment.
AC electrical equipment (such as motors) are provided with voltage by two "leads" (at least for two phase 120V devices), one of which is the "hot" lead and the other is a "neutral" lead. The neutral lead (by convention) is a white wire, and the hot is a black wire. In 220V circuits in the USA, there are two hot leads (one black and the other red). The "ground lead" is by convention either a bare copper wire or if insulated it is green. This lead is at "ground" or "earth" potential and is connected to a "grounding" conductor somehow imbedded in the earth. You might imagine that the "neutral" lead for AC devices should be identical to a "grounding" lead, but it really isn't. To understand why, you have to know how AC transformers that supply domestic power work. For many years residential 120VAC power was supplied to US homes with two wires (one hot and the other neutral). The house electrical outlets had only two slots to deliver this power to homes. Current electrical codes require outlets with three slots: for a hot, neutral, and grounding appliance conductor. The grounding conductor is electrically connected to the appliance in such a way that if there is an electrical short circuit in the appliance, current will trip the circuit breaker or fuse and de-energize the appliance so as to prevent an electrical shock to the user.
A step up in electrical safety from this 3-wire (hot, neutral, and ground) system is the GFI system, currently required by electrical codes for outlets used in certain situations (such as in bathrooms and kitchens where there are higher risks of electrical shock from faulty appliances).
AC electrical equipment (such as motors) are provided with voltage by two "leads" (at least for two phase 120V devices), one of which is the "hot" lead and the other is a "neutral" lead. The neutral lead (by convention) is a white wire, and the hot is a black wire. In 220V circuits in the USA, there are two hot leads (one black and the other red). The "ground lead" is by convention either a bare copper wire or if insulated it is green. This lead is at "ground" or "earth" potential and is connected to a "grounding" conductor somehow imbedded in the earth. You might imagine that the "neutral" lead for AC devices should be identical to a "grounding" lead, but it really isn't. To understand why, you have to know how AC transformers that supply domestic power work. For many years residential 120VAC power was supplied to US homes with two wires (one hot and the other neutral). The house electrical outlets had only two slots to deliver this power to homes. Current electrical codes require outlets with three slots: for a hot, neutral, and grounding appliance conductor. The grounding conductor is electrically connected to the appliance in such a way that if there is an electrical short circuit in the appliance, current will trip the circuit breaker or fuse and de-energize the appliance so as to prevent an electrical shock to the user.
A step up in electrical safety from this 3-wire (hot, neutral, and ground) system is the GFI system, currently required by electrical codes for outlets used in certain situations (such as in bathrooms and kitchens where there are higher risks of electrical shock from faulty appliances).
Thank you for your detailed explanation. I asked this question because a passage question came up where it was asked why touching a charged sphere, with a certain voltage, was not lethal. I said that it was because the sphere was grounded, but the answer said that it could not be grounded because no charge would be able to form on the outside. Does grounding prevent charges from forming on the surface of whatever is being grounded?
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Grounding is the act of removing charge from an object.
Therefore a charged sphere cannot be grounded, because it would not be charged if it was grounded.
A charged sphere will generally be isolated if in equilibrium or having some force act upon it (in problems).
Therefore a charged sphere cannot be grounded, because it would not be charged if it was grounded.
A charged sphere will generally be isolated if in equilibrium or having some force act upon it (in problems).
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I looked through the PS topic list and didn't see anything referring to grounding.
I am currently taking E&M - here is the small amount of info Giancoli has on it.
Grounding is the act of connecting an object to a large reservoir (ie Earth) that can easily give or receive electrons.
There is a small section on "Electrical hazards".
Electrical shock can cause death through burns or inducing VFib in the heart - starting at a current of 80 to 100 mA.
Shock seriousness depends on voltage and the resistance of body. Resistance of skin can range from 10^3 to 10^6 ohms.
So it depends on the potential of the sphere as to the seriousness of the injury based on the current that is passed through the body as seen in Ohm's law. I=V/R
Assuming a resistance of 1000 ohms (wet skin) - a voltage of 120V could cause current: I=V/R=120V/1000 ohm = 120 mA which is potentially lethal.
I think the above paragraph will help you the most - it is my paraphrase of what I learned reading section 26-6 of Giancoli physics text.
I am currently taking E&M - here is the small amount of info Giancoli has on it.
Grounding is the act of connecting an object to a large reservoir (ie Earth) that can easily give or receive electrons.
There is a small section on "Electrical hazards".
Electrical shock can cause death through burns or inducing VFib in the heart - starting at a current of 80 to 100 mA.
Shock seriousness depends on voltage and the resistance of body. Resistance of skin can range from 10^3 to 10^6 ohms.
So it depends on the potential of the sphere as to the seriousness of the injury based on the current that is passed through the body as seen in Ohm's law. I=V/R
Assuming a resistance of 1000 ohms (wet skin) - a voltage of 120V could cause current: I=V/R=120V/1000 ohm = 120 mA which is potentially lethal.
I think the above paragraph will help you the most - it is my paraphrase of what I learned reading section 26-6 of Giancoli physics text.
