A sensor is exposed for time 
to a lamp of power 
placed at a distance l. The sensor has a circular opening that is 
in diameter. Assuming all energy of the lamp is given off as light, the number of photons entering the sensor if the wavelength of light is 
, is ( 
)
A
B
C
D
Text Solution
Verified by ExpertsThe correct answer is:
A
Energy emitted by the lamp in time 
If 
is the radius of the sphere and 
is the distance of source, then the energy reaching the sphere.
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