Laser beams are sometimes used to burn away cancerous tissue. show answer Incorrect Answer What is the intensity, in watts per square meter, of a laser beam that is 90.0% absorbed by a 1.95-mm diameter spot of cancerous tissue and must deposit 495 J of energy to it in a time period of 3.8 s

The intensity of the beam is

Explanation:

We can find the intensity absorbed by the spot cancerous tissue with the equation:

(1)

with P average power and A the effective area. Average power is the energy (E) absorbed in a certain time (t) so:

(2)

Using (2) on (1)

(3)

We can assume the area of the spot as a circumference of radius (r) 1.95 mm or so the area of a circumference with this radius is:

Using this value on (3)

(3)

Because the tissue only absorbs 90% of the intensity the total intensity, we can use the relation:

to find the intensity of the beam (I):

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