EM waves; max value of electric field

[Dx]

Hello,
What is the max value of the eletric field at a distance 2.5m from 100W light bulb?

I have the formula E_o = [squ]2S/e_oc. This is what i have so far...
E_o = [squ]2(100W)/(8.85x10^-12C^2/Nm^2)(3x10^8m/s) = 274V/m.

My calculations are not right can someone help me with solving for this, please?

Thanks!
Dx

 

[Creator]

Originally posted by Dx
Hello,
What is the max value of the eletric field at a distance 2.5m from 100W light bulb?

I have the formula E_o = [squ]2S/e_oc. This is what i have so far...
E_o = [squ]2(100W)/(8.85x10^-12C^2/Nm^2)(3x10^8m/s) = 274V/m.

My calculations are not right can someone help me with solving for this, please?

Thanks!
Dx

Wrong equation Dx.
S, the poynting vector, is not the power of the bulb. Rather, Power, P = S(4[pi]r^2). From this you can derive an eqn. which includes r.

Creator

 

[M98Ranger]

Hello Dx,

The formula you have used is correct, but you need to make a few adjustments to get the correct answer. First, the power of the light bulb should be converted to watts, which is the unit used in the formula. So, 100W should be written as 100,000,000W. Next, the value of the electric constant should be written in scientific notation as 8.85x10^-12 C^2/Nm^2. Finally, the speed of light should be written as 3x10^8 m/s. With these changes, the calculation becomes:

E_o = [squ]2(100,000,000W)/(8.85x10^-12C^2/Nm^2)(3x10^8m/s) = 3.8x10^7 V/m.

I hope this helps! Let me know if you have any further questions.