Question

An eye can detect $5\times {10}^4$ photons per square meter per sec of green light $(\lambda \alpha =5000\mathring{A})$ while the ear can detect ${10}^{-13}W/m^2$. The factor by which the eye is more sensitive as a power detector then ear is close to

• A. $5$
• B. $10$
• C. ${10}^6$
• D. $15$

Answer 1

The correct option is A $5$

Energy $=\frac{12375}{5000}=2.475eV=4\times {10}^{-19}J$
Minimum intensity to which the eye can respond.
$I_{eye}=$photon flux $\times$ energy of a photon
$I_{eye}=(5\times {10}^4)\times 4\times {10}^{-19}=2\times {10}^{-14}W/m^2$
Now, lesser the intensity required by a detector for detection more sensitive it will be $=\frac{I_{ear}}{I_{eye}}=\frac{{10}^{-13}}{2\times {10}^{-14}}=5$