Suppose an air-gap capacitor has circular plates of radius R = 3.2 cm and separation d = 1.8 mm. A 91.0-Hz emf, ε=ε0cos(ωt) , is applied to the capacitor. The maximum displacement current is 40μA. Determine (a) the maximum conduction current I, (b) the value of ε0, (c) the maximum value of (dφe/dt) between the plates.

Respuesta :

Answer:

(a) The maximum conduction current is [tex]40 \times 10^{-6}[/tex] A

(b) Value of [tex]\epsilon _{o} = 4.41 \times 10^{3}[/tex] V

(c) Maximum value of [tex]\frac{d\phi}{dt} = 4.5 \times 10^{6}[/tex] [tex]\frac{V}{m}[/tex]

Explanation:

Given:

Radius of circular plates [tex]R = 3.2 \times 10^{-2}[/tex] m

Separation between plates [tex]d = 1.8 \times 10^{-3}[/tex] m

Frequency [tex]f = 91[/tex] Hz

Maximum displacement current [tex]I_{d} = 40 \times 10^{-6}[/tex] A

(a)

Displacement current is equal to the conduction current so we write,

[tex]I _{max} = 40 \times 10^{-6}[/tex] A

(b)

From the formula of displacement current,

 [tex]I _{d} = \frac{\omega \epsilon _{o} \mu_{o} \pi r^{2} }{d}[/tex]

Where [tex]\mu _{o} = 8.85 \times 10^{-12}[/tex], [tex]\epsilon _{o} =[/tex] peak value of emf, [tex]\omega = 2\pi f[/tex]

  [tex]\epsilon _{o} = \frac{I_{d} d}{2\pi f \times \mu_{o} \times \pi r^{2} }[/tex]

  [tex]\epsilon _{o} = \frac{40 \times 10^{-6} \times 1.8 \times 10^{-3} }{6.28 \times 91 \times 8.85 \times 10^{-12} \times 3.14 (3.2 \times 10^{-2} )^{2} }[/tex]

   [tex]\epsilon _{o} = 4.41 \times 10^{3}[/tex] V

(c)

From another formula of displacement current,

  [tex]I_{d} = \mu_{o} \frac{d\phi}{dt}[/tex]

Where [tex]\frac{d\phi}{dt} =[/tex] change in flux

  [tex]\frac{d\phi}{dt} = \frac{40\times 10^{-6} }{8.85 \times 10^{-12} }[/tex]

 [tex]\frac{d\phi}{dt} = 4.5 \times 10^{6}[/tex] [tex]\frac{V}{m}[/tex]

Therefore, the maximum conduction current is [tex]40 \times 10^{-6}[/tex] A and value of

[tex]\epsilon _{o} = 4.41 \times 10^{3}[/tex] V and maximum value of [tex]\frac{d\phi}{dt} = 4.5 \times 10^{6}[/tex] [tex]\frac{V}{m}[/tex]