Laser Beam Intensity: Solve W/m², J, & mm | Help Needed

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Homework Help Overview

The discussion revolves around calculating the intensity of a laser beam used in a medical context, specifically for burning cancerous tissue. The problem involves energy absorption, area calculations, and time considerations, with a focus on understanding the relationship between these variables.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • The original poster attempts to calculate the intensity based on energy, area, and time, expressing difficulty in arriving at the correct answer. Some participants suggest starting with a scenario of 100% absorption to simplify the calculations and then adjusting for the actual absorption rate. There is also a query about comparing the laser intensity to that of direct sunlight.

Discussion Status

Participants are actively engaging with the problem, offering guidance on how to approach the calculations. There is acknowledgment of the original poster's progress, with one participant confirming a successful calculation. However, questions remain regarding the comparison of laser intensity to sunlight intensity, indicating ongoing exploration of the topic.

Contextual Notes

Participants are working under a time constraint, as the original poster has a deadline for the assignment. There is also a mention of needing to convert units from millimeters to meters for accurate area calculations.

CMATT
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Thread moved from the technical forums -- poster has been reminded of the PF rules
What is the intensity in W/m² of a laser beam used to burn away cancerous tissue that, when 94.0% absorbed, puts 539 J of energy into a circular spot 2.11 mm in diameter in 4.00 s??

I've tried a couple different equations and I keep getting the answer wrong. This is due tonight, I'm super stuck. Any input is greatly appreciated
 
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First imagine the beam is 100% absorbed, find that answer, and multiply that answer by 1/.94 to get the answer for 94% absorbed. To get the 100% absorbed answer, just take that energy, per that area, per that time. You will have to convert mm to m though, and you will need to know the area of a circle.
 
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Ken G said:
First imagine the beam is 100% absorbed, find that answer, and multiply that answer by 1/.94 to get the answer for 94% absorbed. To get the 100% absorbed answer, just take that energy, per that area, per that time. You will have to convert mm to m though, and you will need to know the area of a circle.

Thank you for your help Ken G! I will try this out right now
 
Ken G said:
First imagine the beam is 100% absorbed, find that answer, and multiply that answer by 1/.94 to get the answer for 94% absorbed. To get the 100% absorbed answer, just take that energy, per that area, per that time. You will have to convert mm to m though, and you will need to know the area of a circle.

Yay I got the correct answer, thank you! Would you happen to know how this one below is solved? I did my answer - 1360 W/m^2, and got a number, but I'm not sure if that's correct:

How many times more intense is this than the maximum intensity of direct sunlight (about 1360 W/m²)?
 
A quick estimate says its about 10,000 times more for the laser. Is that about what you got?
 

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