8: Lightning

Question 1

Electricity Basis (V, E, Q, I, P, R)

Answer 1

• V: electric potential (Volt)
• E: electric field = rate of change of electric potential with height (Volt/m)
• Q: electric charge (Coulomb)
• I: electric current (Ampere = Coulomb/sec)
• P = V x I –> electric power (Watt = VA) (know)
• R = V/I –> resistance (Ohm) (know)
• C = Q/V –> capacitance (Farad)

Question 2

Ohm’s Law

Answer 2

• To calculate resistance
• VIR (triangle)
• V on top, I to the left and R to the right

Question 3

The Earth’s Charge

Answer 3

• the Earth is electrically charged and acts as a spherical capacitor
• the Earth has a net negative charge of about a half million Coulombs, while an equal positive charge resides in the atmosphere

Question 4

What is a capacitor

Answer 4

• holds energy between regions of positive and negative charges
• used to store energy in the form of an electrostatic field between its plates
• Used to buffer power
• Will drain over time if not recharged

Question 5

What is the Electrosphere

Answer 5

• Positive charge of the atmosphere
• The electrical resistivity of the atmosphere decreases with height to an altitude of about 50km, where the resistivity becomes constant –> region is known as the electrosphere

Question 6

Fair Weather Electric Field

Answer 6

• there is a small current between the electrosphere (positive) and the Earth (negative) because earth is not a perfect insulator –> called the fair weather electric current

Question 7

Fair Weather Capacitor and what would happen if left alone?

Answer 7

Compared to air, humans have low ressitance so we dont feel the 200V differential from head to toe

If left alone, the capacitor would discharge:
* Charge on Earth’s surface = 5x10^5 Coloumbs (negative)
* Charge in atmophere = 5x10^5 Coloumbs (positive)
* In 5.5 minutes, the Earth/atmosphere would lose its charge

Question 8

What maintains the charge in our capacitor

Answer 8

• Thunderstorms and lightning
• Thunderstorm system acts as a bettery to keep the fine weather capacitor charted by providing a negative current to the ground

Question 9

HOw many thunderestorms in progress around the world at one time

Answer 9

2000 thunderstorms, producing about 30 to 100 cloud to ground flashes each second or about 5 million flashes a day

Question 10

Recharging the Capacitor

Answer 10

• each storm produces one lightning strike every 13 seconds
• each lightning strike transfers 10 Coulombs of negative charge to the Earth’s surface
• Negative current to ground: I = 150 strikes/sec x 10 Coulombs = 1500 amperes
• This balances the fair weather current and maintains the charge in the capacitor