Question

Damage caused to human eyes by laser light is dependent on the frequency of the laser, as well as the exposure time. For red laser light, a typical value for the amount of energy per square meter that would cause damge is 10J/m2. How long could someone stare directly at this supermarket checkout laser before damage occurs

Answer 1

t = 3.14 10⁻² s

Step-by-step explanation:

The typical lasers of the barcode readers are of the order of mW, which we look for the energy per unit of time

E = P t

The diameter of these lasers is of the order of a few centimeters

The area of ​​a circle is

A = π r²

A = π (1 10⁻²) = 3.14 10⁻⁶ m²

As the data they give is the intensity, we calculate with a rule of direct proportions the energy in the area of ​​the laser reader

10 j in 1 m² what is the energy in 3.14 10⁻⁶ m²

E = 10 J / m² 3.14 10⁻⁶ m²

E = 3.14 10⁻⁵ J

Suppose the reader's power is 1 mW, let's calculate the time to reach the previously calculated power

t = E / P

t = 3.14 10⁻⁵ / 1 10⁻³

t = 3.14 10⁻² s

So seeing these lasers directly causes vision damage very quickly.