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

Answer

1

Explanation

Number of photons entering sensor are
`N=(P_(i) lambda t)/(hc)" "( P_(i) rarr" incident power")`
Where `P_(i)=P/(4pi l^(2))xx pi (2d)^(2)`
`implies N=(P lambda d^(2) t)/(hcl^(2))`