Calculating Average Intensity of a laser blackboard pointer

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    Average Intensity
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Homework Help Overview

The discussion revolves around calculating the average intensity of a laser blackboard pointer, which delivers 0.10 mW of power through a beam with a diameter of 0.90 mm. Participants are exploring the relationships between power, intensity, and the electric and magnetic fields associated with the laser beam.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to use a formula for average intensity but questions whether they are using the correct formula or value for the radius. Other participants suggest that the average power should be measured over the area of the beam and discuss the formula used for intensity, raising questions about the parameters involved.

Discussion Status

Some participants have provided calculations and insights regarding the average intensity, while others are still grappling with the relationships between the different quantities involved. There is a mix of attempts to clarify the formulas and assumptions, with some participants indicating they have made progress on subsequent parts of the problem.

Contextual Notes

Participants are working under the constraints of needing to find the average intensity before proceeding to calculate the electric and magnetic fields. There is an ongoing discussion about the correct interpretation of the formula and the parameters involved, particularly regarding the radius and area of the beam.

patelpalak
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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 can't do anythin bout it because i need the average intensity
in order to find the elecric and magnetic fields.

somebody plez help me asap...thanx!
 
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Isn't the power measured in the area of the beam?

Avg power = .1*10-3w / (3.14*(.45*10-3m)2) = ... w/m2
 
LowlyPion said:
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 isn't the
formula is ave s= p/4*pie*r^2 ?
 
patelpalak said:
is there 4 in the bottoom becuz isn't 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.
 
ok i got 160 W/m^2
thanx for the help!
 
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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