Laser Safety A 0.50 m W laser emits a narrow beam of light that enters the eye,

Question

Laser Safety A 0.50mW laser emits a narrow beam of light that enters the eye, as shown in the figure

Part A

How much energy is absorbed by the eye in 0.20s?

Express your answer using one sigfig.

E=mJ

Part B

The eye focuses this beam to a tiny spot on the retina, perhaps 5.0 ?m in diameter. What is the average intensity of light at this spot?

Express your answer using two sigfigs.

I=kW/cm^2

Part C

Damage to the retina can occur if the average intensity of light exceeds 1.0X10^-2 W/cm^2.

By what factor has the intesity of this laser beam exceeded the safe value?

Express your answer using two sigfigs.

f=

Explanation / Answer

a) E = P t = 0.5*0.2=0.1 mJ

b)I = 0.5E-3/(pi*2.5E-6^2)=2.55E7 W/m^2 = 2.55E4 kW/m^2 = 2.55 kW/cm^2

c) 2.55E3/1.0E-2=2.55E5

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