Question

Consider a 5 m long, air-filled section of a coaxial transmission line, given that the radius of the inner conductor is 10 cm and the inner radius of the outer conductor is 20 cm? If the current is 100 mA, how much magnetic energy is strored in the air medium between the conductors. This problem is similar to Example 2 in the Time Varying Fields folder in the Example Bank.
a) 200.89 nj
b) 3.47 nj
c) 10.45nj
d) 80.9nj

Answer 1

Answer: b) 3.47 nj

Explanation:

Given that;

length l = 5m

radius of inner conductor r = 10cm = 0.1m

radius of outer conductor D = 20cm = 0.2m

current I = 100A = 100×10⁻³ = 0.1

medium between conductor in air u₀ = 4π × 10⁻⁷

Energy in a coaxial cable transmission line is

w = u₀ /2π I² en(b/a)

we substitute

L = 4π × 10⁻⁷ /4π ×10⁻²× 5 en (20/10)

L =3.4657 × 10⁻⁹ J

L = 3.4657 nJ ≈ 3.47 nJ