Register to reply 
Calculating values of electric and amgnetic fields of laser beam 
Share this thread: 
#1
Nov1910, 11:39 AM

P: 22

1. The problem statement, all variables and given/known data
A continuous wave laser beam in free space carries a power of 15w and has a circular cross section with diameter 1mm. Calculate peak values of the oscillatory electric and magnetic fields Eo and Ho repectively. 2. Relevant equations Eox = ([tex]\mu[/tex]/[tex]\epsilon[/tex])^1/2 Hoy [tex]\pi[/tex]r^2 Energy flow = 1/2 (HE + EH) energy flow =  E x H  E = Eo cos ([tex]\omega[/tex] t ) 3. The attempt at a solution Okay so i have the energy flow as 19098.593 Kj / s / m^2 I know energy flow = 1/2 \HE + EH ) = EH = E x H this energy flow is in direction of wave.. But i cant work out how to relate this to get the mag of electric field or magnetic field 


#2
Nov1910, 01:14 PM

Sci Advisor
P: 2,659

Since you are in vacuum, I don't think there's any reason to complicate things. E=cB, and B=μ_{0}H



#3
Nov1910, 01:16 PM

P: 22




#4
Nov1910, 02:11 PM

Sci Advisor
P: 2,659

Calculating values of electric and amgnetic fields of laser beam
Just invert the second equation for H in terms of B.



#5
Nov1910, 02:48 PM

P: 22

Sorry, i mean to say i dont know how i would get H B or E.
i can see easily how with any of the variables allows the other for calculation but im at a loss to get any. 


#7
Nov1910, 04:20 PM

P: 22

for fear of asking the obvious, S being?



#8
Nov1910, 09:00 PM

Sci Advisor
P: 2,659

S bar is the average of the magnitude of the Poynting Vector, it is the flux (or intensity) of the laser measured in Watts per meter squared.



#9
Nov2010, 08:23 AM

P: 22

Ok, didnt realise that equation,
so using those values E = [tex]\sqrt{2S\mu c}[/tex] ? Therefore E = 119959.9933 V m^1 ? H = E/c[tex]\mu[/tex] ? Therefore H = 318.4160428 A m^1 ? I tried to confirm the equations using dimensional analysis: E = V m^1 mu= kg·m·s−2·A−2 C = m S^1 S = J s^1 m^2 I cant get that to equal but i think i may be rearranging wrong. Thankyou for yor help so far 


Register to reply 
Related Discussions  
Calculation of an Electron Beam path when subjected to magnetic and electric fields  Classical Physics  17  
Calculating Multiple Integrals on Mathematica (Electric fields)  Advanced Physics Homework  1  
Calculating Ka and Kb values from estimated pH values  Biology, Chemistry & Other Homework  4  
Calculating electric fields through integration  General Physics  3  
Calculating electric fields  Introductory Physics Homework  1 