An LED made of a semiconductor material with a bandgap of 2.0 eV emits light with an optical power output of 3.2 mW . Assuming 100 % efficiency in converting electrical energy into light, the number of photons emitted per second is: (Take 1 eV = 1.6 10⁻¹⁹ J )

Step-by-step solution

First, find the energy of a single emitted photon. For an LED, the photon energy is approximately equal to the bandgap energy: E = 2.0 eV Convert this energy into Joules: E = 2.0 1.6 10⁻¹⁹ J = 3.2 10⁻¹⁹ J The optical power output is the total energy emitted per second: P = 3.2 mW = 3.2 10⁻³ W (or J/s) The power is related to the number of photons emitted per second ( n ) by the equation: P = n E Rearranging to solve for n : n = P E = 3.2 10⁻³ 3.2 10⁻¹⁹ n = 10¹⁶ photons/s Thus, 10¹⁶ photons are emitted per second. A