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Assume Earth and a cloud layer 770 m above the Earth can be treated as plates of a parallel-plate capacitor.

a) If the cloud layer has an area of 1 x 106 m2, what is the capacitance?
b) If an electric field strength of 2 x 106 N/C causes the air to conduct charge (lightning), what charge can the cloud hold

1 Answer

7 votes

Answer:

(a) 1.15×10⁻⁸ F.

(b) 1.5×10⁻⁸ C.

Explanation:

(a)

Capacitance of a capacitor: This is the ability for a capacitor to store charge.

The S.I unit of capacitance of a capacitor is Farad (F).

Mathematically, it is represented as

C = ε₀A/d² ................. Equation 1

Where C = Capacitance of the capacitor, ε₀ = permitivity of free space, A = area of the plates, d = distance between the plates.

Given: A = 1×10⁶ m². d = 770 m

Constant: ε₀ = 8.85×10⁻¹² F/m

Substituting these values into equation 1

C = 8.85×10⁻¹²(1×10⁶ )/770

C = 8.85×10⁻⁶/770

C= 0.0115×10⁻⁶

C = 1.15×10⁻⁸ F.

Thus the capacitance of the cloud layer = 1.15×10⁻⁸ F.

(b)

Electric Field Strength: This is the force per unit charge which is exerted at a point in a in a electric field.

It can be represented mathematically as

E = kq/d²........................... Equation 2

Where E = Electric Field Strength, q = charge, d = distance. k = proportionality constant.

Making q the subject of the equation above,

q = Ed²/k ........................... Equation 3.

Given: E = 2×10⁶ N/C, d = 770 m

Constant: k = 1/4πε₀ = 9×10⁹ Nm²/C²

Substituting these values into equation 3

q = 2×10⁶(770)²/(9×10⁹)

q = (2×10⁶)(592900)/(81×10¹⁸)

q = 14639.5×10⁻¹²

q ≈ 1.5×10⁻⁸ C.

Thus the charge the cloud can hold = 1.5×10⁻⁸ C.

User Sanjay Yadav
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