Question

A). what is the intensity in W/m2 of laser beam used to burn tissue that, when 90% absorbed, puts 520J of energy into a circular spot of 2 mm in diameter in 4 s?

B). compare this intensity to the average intensity of sunlight (about 1 kW/m2)

* *intensity of laser/ avg intensity of sunlight=

C). what is the intensity ratio in dB?

intensity ratio is?

Answer 1

A.Intensity=energy transmitted per unit area per unit time=E/(A*t) , where E is the energy,A is area, t is time

The given problem says that when 90% of the beam is absorbed , it supplies 520 J of energy into a circular spot of 2mm in diameter in 4 seconds.

Let the total amount of energy supplied is E

Then, 90% of E=520=> 90/100*E=520

=>E=520*10/9=577.78 J

t=4s

Area of circle A=(radius)) ^{2 is first} =(diameter/2)²

Here,diameter = 2mm= 0.002 m

So,A=(0.002/2)² =(0.001)² m²

So,I=E/(A*t)=577.78/[(0.001)²*4]=4.60*10⁷ W/m²

B.Intensity of sunlight= 1kW/m²=1000 W/m²

Clearly,intensity of laser is more than that of sunlight.

(intensity of laser)/(average intensity of sunlight)=4.60*10⁷/1000=4.60*10⁴ W/m²

C.intensity ratio in dB=10 log₁₀(I₁/I₂) where I₁ is first intensity,I₂ is second intensity

So,intensity ratio=10 log₁₀(4.60*10⁴ )=46.63 dB