 Well, it's Friday night again and after a week of struggling through physics. Yeah, I'm just gonna grab one of those You walk over to the disco when suddenly you realize your favorite man ever is playing its teacher band They just keep getting better and better But there's a problem see there's a big scary bouncer outside the door And he says there's a cover charge of three dollars, which is an issue because you only have two dollars So you decide to go and see if you can get in any ways and you say hi I have two dollars. Is that enough and He is not saying much so at this point you're pretty sure it's either three dollars or nothing is gonna happen here tonight So you get on the phone to call a friend to see if you can borrow some money when you realize You don't really have any friends. The only number in your phone is your mom So you call your mom and you say hey mom is there any way you can lend me some money I want to get into the show and she says sure I'll come to the concert with you, sweetie And she shows up at the disco and she's brought two dollars Which is annoying? So you try the bouncer again because maybe he's not the sharpest tool in the shed But even he can work out that four dollars does not work for two people to get in and he sends you away Just as your mom leaves you look down at the street and what do you see but another two dollars? So now you can finally go in pay the bouncer three dollars Get into the show have enough change left over to buy a caffeine-free diet cola and dance the night away This is exactly the way the photoelectric effect works Or maybe it's an analogy of how Einstein explained this effect In the photoelectric effect light falling on a metal surface produces current this phenomenon was discovered in 1839 But Einstein didn't provide his explanation until after his work on the photon model of light in 1905 Here's the basics of how he explained the photoelectric effect Light thought of here as a photon is incident or it hits a metal surface in my analogy You are this photon of light and the bouncer is the metal the light has a certain amount of energy Which is related to its frequency or its wavelength through Planck's equations and energy in my analogy is the money When the light hits the metal the photon might cause the metal to release an electron now There are two things that decide this one the amount of energy the photon has like the money you had when you were trying to get into the show and To the amount of energy the metal needs to be given to allow an electron to be released This is sort of like the cover charge. We call this amount of energy the work function of the metal if The instant photon doesn't have enough energy then it does not release an electron Einstein noted that it didn't matter if multiple photons all with less than this amount of energy hit the metal Giving a total energy over the work function each photon needs to essentially pay its own cover charge That's why you and your mom couldn't both get in even though you had a total of four dollars When a photon has just enough energy to pay the work function We say that this photon is at the threshold frequency The threshold frequency is the minimum frequency needed for the light to cause electrons to be released is Related to the work function of the metal by the equation W equals h f naught If the photon is extra energy the law of conservation of energy tells us that the extra energy has to go somewhere So it turns into kinetic energy in the electron called the ek max in This analogy I sort of think of this extra kinetic energy as the change left over that she used to buy that sweet caffeine-free diet soda This energy can be calculated in the physics 20 way using kinetic energy equals one half mv squared Or using the formula ek max equals q v stop where q is the charge of the electron and v stop is the stopping voltage Or the voltage needed for an electric field also president Einstein's experimental design to stop the electron To put it all together when you go out on a Friday night the money you initially have goes to places To the bouncer to pay the cover charge and the leftover change you spend on soda and When a photon of light hits a metal surface the energy from the instant photon of light goes to places To the work function of the metal and to kinetic energy in the electron Now you can walk the night away