A light bulb emits light uniformly in all directions. The average emitted power is 150.0 W. At a distance of 5 m from the bulb, determine (a) the average intensity of the light, (b) the rms value of the electric field, and (c) the peak value of the electric field.

Respuesta :

Answer:

a) 0.477 W/m²

b) 13.407 N/C

c) 18.96 N/C

Explanation:

P = Power = 150 W

r = Distance = 5 m

ε₀ = Permittivity of space = 8.854×10⁻¹² F/m

a) Average intensity

[tex]\bar{S}=\frac{P}{A}\\\Rightarrow \bar{S}=\frac{150}{4\pi r^2}\\\Rightarrow \bar{S}=\frac{150}{4\pi 5^2}\\\Rightarrow \bar{S}=0.477\ W/m^2[/tex]

∴ Average intensity is 0.477 W/m²

b) Rms value

[tex]\bar{S}=c\epsilon_0E_{rms}^2\\\Rightarrow E_{rms}=\sqrt{\frac{\bar{S}}{c\epsilon_0}}\\\Rightarrow E_{rms}=\sqrt{\frac{\bar{0.477}}{3\times 10^8\times 8.854\times 10^{-12}}}\\\Rightarrow E_{rms}=13.407\ N/C[/tex]

∴ Rms value of the electric field is 13.407 N/C

c) Peak value

[tex]E_0=\sqrt 2E_{rms}\\\Rightarrow E_0=\sqrt 2\times 13.407\\\Rightarrow E_0=18.96\ N/C[/tex]

∴ Peak value of the electric field is 18.96 N/C

The average intensity of the light, rms value of the electric field and peak value of electric field are respectively; 0.477 W/m²; 13.407 N/C; 18.96 N/C

What is the value of the electric field?

We are given;

Power; P = 150 W

Distance; r = 5 m

A) Formula for average intensity is;

I = P/A

Where A is area = 4πr² = 4π(5²)

A = 100π

I = 150/(100π)

I = 0.477 W/m²

B) Formula for the rms value of the electric field is;

E_rms = √(I/(ε₀ * c))

where;

ε₀ is permittivity of free space = 8.854 × 10⁻¹² F/m

c is speed of light = 3 * 10⁸ m/s

Thus;

E_rms = √(0.477/(8.854 × 10⁻¹² * 3 * 10⁸))

E_rms = 13.407 N/C

C) The peak value of the electric field is;

E₀ = E_rms * √2

E₀ = 13.407 * √2

E₀ = 18.96 N/C

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