Answer:
t = 3.14 10⁻² s
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.
