Question

The sensor is exposed for $0.1s$ to a $200W$ lamp $10m$ away. The sensor has opening that is $20mm$ in a diameter. How many photons enter the sensor if the wavelength of light is $600mm$? (assume that all the energy of the lamp is given off as light).

• A. $1.53\times {10}^{11}$
• B. $1.53\times {10}^2$
• C. $1.53\times {10}^4$
• D. $1.53\times {10}^{13}$

Answer 1

Answer: (D)

$1.53\times {10}^{13}$

(Refer to Image)

Energy incident on sensor= $n\frac{hc}{x}$

$=\frac{\pi \left(\frac{20}{1000}\right)\times \frac{1}{4}}{4\pi (10{)}^2}\times 200\times \frac{1}{10}=x\times \frac{6.626}{{10}^{34}}\times \frac{3\times 100}{600}$

$\Rightarrow n=1.53\times {10}^{13}$