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Average intensity

  • Thread starter patelpalak
  • Start date
  • #1

Homework Statement



A laser blackboard pointer delevers 0.10-mW average power in a beam 0.90 mm in diameter.

Homework Equations



a) Find the average intensity.
b) Find the peak electric field.
c) Find the peak magnetic field.



The Attempt at a Solution



ok for part a) i used the formula ave. s = p/4 pie r^2 (as p=.10 mW and r=0.45 mm)
but i didnt get the right answer
so am i using the wrong formula or the wrong value for r?


for part (b) and (c) i cant do anythin bout it cuz i need the average intensity
in order to find the elecric and magnetic fields.

somebody plez help me asap....thanx!!
 

Answers and Replies

  • #2
LowlyPion
Homework Helper
3,090
4
Isn't the power measured in the area of the beam?

Avg power = .1*10-3w / (3.14*(.45*10-3m)2) = ... w/m2
 
  • #3
Isn't the power measured in the area of the beam?

Avg power = .1*10-3w / (3.14*(.45*10-3m)2) = ... w/m2

is there 4 in the bottoom becuz isnt the
formula is ave s= p/4*pie*r^2 ?
 
  • #4
LowlyPion
Homework Helper
3,090
4
is there 4 in the bottoom becuz isnt the
formula is ave s= p/4*pie*r^2 ?
That r is for distance isn't it?

This is a laser beam and I'd say dispersion is minimal, so you only want the cross section of the beam.
 
  • #5
ok i got 160 W/m^2
thanx for the help!!!!
 
  • #6
hey i got part b
but have problem with part C

is this right?

B^2 = ave. S *2* 4*pie*10^-7/ (3*10^8) = T
 

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