#Equation to calculate light intensity how to

#Equation to calculate light intensity how to

Let's solve some numericals on quantum nature of light on photons here's the first one we have a bulb of 100 watt 100 watt light bulb that's giving out a light of frequency 4 times 10 to the 14 hertz now according to the quantum nature the bulb is releasing photons it's emitting photons and so the question is how many photons are being emitted per second by this light bulb how do we solve this the first thing that comes to my mind is i know how to calculate energy of a single photon that is from planck's equation it's going to be the planck's constant h multiplied by the frequency of light so that's energy of a single photon and i know planck's constant i know the frequency so i can calculate the energy of each photon okay now from that how do i calculate the number of photons emitted per second how do i do that well i'm given the power output meaning i know that this bulb is emitting 100 joules of energy per second that's the meaning of what let me write that down so i know power is 100 joules per second this much energy is given out per second now using this and the energy and i know the energy of the photon how do i figure out the number of photons emitted per second can you pause and think about it all right so to relate these two if i can relate these two i'm done this is sort of like total energy and this is like energy of one photon so i can just relate them so the way i like to relate them is let's say this number number of photons emitted per second let's say this is n if there are n photons coming out per second and if each photon has this much joules of energy then the total energy coming out per second must be n times e right think about it if this was 2 joules and there are 100 photons coming out per second that means total energy would be 100 times 2 200.