In summary, a thunderstorm causes movement of water molecules within clouds which creates friction. This causes the bottom of the clouds to become negatively charged. Once the electric field between the clouds and the ground becomes larger than 3.0 x 10^6 N/C, lightning will strike.
  • #1
EmilyBergendahl
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Homework Statement


During a thunder storm, movement of water molecules within clouds creates friction which causes the bottom of the clouds to become negatively charged. This means that the bottom of the cloud and the ground begin to act like parallel plates. Once the electric field between the clouds and the ground becomes larger than 3.0 x 10^6 N/C, lightning will strike.
a. If the bottom of the cloud is 150 m above the ground, determine the electric potential difference between the ground and the cloud.
b. Say 6.24 x 10^18 electrons move between the ground and the cloud during a lightning strike. How much electric potential energy does this represent? Are the electrons gaining or losing energy?

Homework Equations


E = V/d
q = Ne
V = E_E/q

The Attempt at a Solution


a.
E = V/d
V = Ed
V = (3.0 x 10^6 N/C)(150 m)
V = 4.5 x 10^8 V

b.
q = Ne
q = (6.24 x 10^18)(-1.6 x 10^19)
q = -0.9984 C
q = -1.0 C

V = E_E/q
E_E = Vq
E_E = (4.5 x 10^8 V)(-1.0 C)
E_E = -4.5 x 10^8 J

How can I tell if the electrons are gaining or losing energy?
 
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  • #2
Math looks good.

Where are the electrons after the strike? Does this represent a change in the potential energy of the electrons? If so, in which direction?
 
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  • #3
Thank you for the response!

I'm not sure if I'm understanding it completely, but if the electrons are moving from the ground (positive plate) to the cloud (negative plate), the electrons would be gaining energy?
 
  • #4
EmilyBergendahl said:
but if the electrons are moving from the ground (positive plate) to the cloud (negative plate)

EmilyBergendahl said:
which causes the bottom of the clouds to become negatively charged
 
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  • #5
Okay. If the bottom of the clouds are negatively charged, that means that an excess of electrons is present. If more electrons move into the clouds, the electrons in the cloud are gaining energy?
 
  • #6
I don't think I'm visualizing this properly...
 
  • #7
EmilyBergendahl said:
Okay. If the bottom of the clouds are negatively charged, that means that an excess of electrons is present. If more electrons move into the clouds, the electrons in the cloud are gaining energy?
Well, I don't know the exact mechanism of lightning phenomenon but from this,
EmilyBergendahl said:
During a thunder storm, movement of water molecules within clouds creates friction which causes the bottom of the clouds to become negatively charged. This means that the bottom of the cloud and the ground begin to act like parallel plates.
I imagine the clouds are negatively charged before the lightning strike. This makes the ground positive w.r.t clouds.
 
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  • #8
EmilyBergendahl said:
I don't think I'm visualizing this properly...
If the clouds are negative and ground is positive, how will be the flow of charge?
 
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  • #9
In the strike, the electrons will be moving from the cloud to the ground. Therefore, the electrons in the cloud are losing energy?
 
  • #10
EmilyBergendahl said:
In the strike, the electrons will be moving from the cloud to the ground. Therefore, the electrons in the cloud are losing energy?
Yes. When a -ve charge is brought closer to a +ve charge, it loses energy and when it is taken away from the +ve charge, it gains energy.
 
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  • #11
Thank you so much again!
 
  • #12
cnh1995 said:
Yes. When a -ve charge is brought closer to a +ve charge, it loses energy and when it is taken away from the +ve charge, it gains energy.
Note that this is about potential energy of the electrons.
 
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  • #13
EmilyBergendahl said:
Thank you for the response!

I'm not sure if I'm understanding it completely, but if the electrons are moving from the ground (positive plate) to the cloud (negative plate), the electrons would be gaining energy?
Yes. Potential energy. As the cloud becomes more and more negatively charged it takes more and more energy to move an electron from the ground to the cloud.

When lightning finally strikes the potential energy is dissipated into light, sound and heat, and who knows what else (e.g. flying debris).

EDIT: the analogy to a capacitor with parallel plates is actually not good. In the capacitor the plates assume a NET charge, in lightning neither the cloud nor the Earth do. The movement of the cloud forces separation of charges so that the bottom of the cloud becomes - and the proximate Earth is induced +. I'm not sure that the electrons actually travel from the cloud to ground as the problem postulates. This is actually a not well understood science even today as I understand it.

.
 
Last edited:

1. What causes electric potential difference during a thunderstorm?

Thunderstorms are caused by the buildup of positive and negative electrical charges within a cloud, with the negative charges typically concentrated at the bottom and the positive charges at the top. This creates an electric potential difference between the top and bottom of the cloud, and between the cloud and the ground.

2. How does electric potential difference affect lightning strikes during a thunderstorm?

The electric potential difference is a key factor in the formation of lightning during a thunderstorm. When the potential difference between the cloud and the ground becomes too great, it can cause a discharge of electricity in the form of a lightning bolt.

3. Can electric potential difference during a thunderstorm be dangerous?

Yes, electric potential difference during a thunderstorm can be dangerous. Lightning strikes can cause severe injuries and even death to humans and animals. Additionally, the electrical charges in the atmosphere during a thunderstorm can also damage electronic equipment and cause power outages.

4. How is electric potential difference measured during a thunderstorm?

Electric potential difference during a thunderstorm can be measured using specialized instruments, such as a lightning detector. These instruments measure the electric field strength and can detect changes in the electrical charge in the atmosphere.

5. Can electric potential difference during a thunderstorm be harnessed as a source of energy?

While electric potential difference during a thunderstorm is a powerful force, it is not currently harnessed as a source of energy. The unpredictable and sporadic nature of lightning strikes makes it difficult to capture and use as a reliable source of electricity.

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