A light-emitting diode (LED) connected to a 3.0 V power supply emits 440 nm blue light. The current in the LED is 11 mA , and the LED is 51 % efficient at converting electric power input into light power output. How many photons per second does the LED emit?

3.73 * 10^16   photons/sec

Explanation:

power supply = 3.0 V

Emits 440 nm blue light

current in LED = 11 mA

efficiency of LED = 51%

Calculate the number of photons per second the LED will emit

first step : calculate the energy of the Photon

E = hc / λ

   =(  6.62 * 10^-34 * 3 * 10^8 )  / 440 * 10^-9

   = 0.0451 * 10^-17  J

Next :

Number of Photon =( power supply * efficiency * current ) / energy of photon

= ( 3 * 0.51 * 11 * 10^-3 ) / 0.0451 * 10^-17

= 3.73 * 10^16 photons/sec

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