A photodiode sensor is used to measure the output of a 300 W lamp kept 10 m away The sensor has an opening of 2 cm in diameter. How many photons enter the sensor if the wavelength of the light is 660 nm and the exposure time is 100 m s . (Assume that all the energy of the lamp is given off as light and h = 6 . 6 × 10 - 34 J s )

Question

A photodiode sensor is used to measure the output of a 300 W lamp kept 10 m away The sensor has an opening of 2 cm in diameter. How many photons enter the sensor if the wavelength of the light is 660 nm and the exposure time is 100 m s . (Assume that all the energy of the lamp is given off as light and h = 6 . 6 × 10 - 34 J s ), 3 . 6 × 10 13, 2 . 8 × 10 13, 2 . 5 × 10 13, 1 . 8 × 10 13

MARKS App · Accepted Answer

Energy of photon is E = h c λ = 6 . 6 × 10 - 34 × 3 × 10 8 660 × 10 - 9 = 3 × 10 - 9 The number of photons emitted is given by, n = Eenergy of lamp Photon energy × Area of sensor Exposure area of lamp ∴ n = 300 × 100 × 10 - 3 3 × 10 - 9 × π × 10 - 2 2 4 π × 10 2 = 2 . 5 × 10 13

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