How To Convert Between Temperature Units

by Patrick Ford
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Hey guys, in an earlier video, we talked about all the different temperature units that we're gonna use in thermodynamics? We talked about Fahrenheit, Celsius and kelvin Now, in some problems you're gonna have to convert between these different temperature units. Some problems will give you a measurement in one unit, like Celsius and you'll have to convert it to another one like kelvin or even Fahrenheit. So I'm gonna show you how to do that in this video, how to convert between the different temperature units. And we're just gonna use this table of equations right here. It's very straightforward to use all we have to do is just locate which units were given which ones we are asked to calculate or asked to convert to and then just use the appropriate equation. So let's go ahead and get started here. So obviously if you are given Fahrenheit and Astro Fahrenheit, you don't have to do anything. Right, there's no conversion, it's the same thing for Celsius and Celsius or Calvin and Calvin, there's no convergence. You have to do where things are a little bit different is if you are given Celsius and then asked for Fahrenheit. So let's take a look at that equation here. So TF the Fahrenheit temperature is going to be 9/5 TC plus 32. Now I'm gonna go in a little bit of a different order because it turns out that when you go diagonally across this table, the equations are gonna be related. So for example, what if I had the opposite, what if I was given Fahrenheit and then asked for Celsius. Now it's the reverse. All you have to do is just take this equation and then solve for T. C. And what you would get is you would get 5/9 and then T f minus 32. You can pause the video and see if you can actually work out and get the same answer. Alright so we're gonna calculate we're actually gonna talk about these equations in just a second here we're gonna go ahead and skip to these two. So a very common one you're gonna have to do is convert between kelvin and Celsius and vice versa. Remember that the kelvin scale and the Celsius scale are the same it's just that one of them is sort of shifted to absolute zero. So a change of one Kelvin is the same thing as a change of one C. So these equations are actually very straightforward and they're very related to each other. All you have to do is just do T k minus 73.15 and that's how you get to Celsius. So if you wanted the opposite equation, if you had Celsius and you wanted kelvin then you would just solve this equation for T. K. And you're gonna get T c Plus to 73.15 right? So all you have to do is just shift back and forth from the absolute zero. Alright so now finally this kelvin to Fahrenheit and vice versa. So we want to kelvin to Fahrenheit, this equation here is gonna be 9/5 T k minus 2, 73.15 plus 32. This might seem really complicated but all really it's happening here is you're actually just sort of merging these two equations together, you're sort of combining them, you got the ninth fist and all that happens here is we're sticking this expression in for T. C. So if you do that, you're basically just gonna get this equation over here. Now, the opposite equation to get from Fahrenheit to kelvin, basically you're just gonna go ahead and solve this T. K. And it's gonna be 5/9 then T f minus Plus to 73.15. So again this equation here is really just a combination of these two equations. So all you really have to memorize, it might look like there's a lot of equations here is really just these two equations. If you remember these two you can get to any of the other ones basically just by flipping some of the variables. Alright, so that's all you really need to know. Let's go ahead and take a look at our example. So we're given a temperature that's in C and we want to convert it to Kelvin that's going to be in part a so we have negative 196° and we want to figure out what is that in kelvin's. Alright, so basically we're given Celsius and were asked for kelvin, So we're just gonna use this equation over here. So this is T. K equals T. C. Plus to 73.15. So this is gonna be T. K. Are temperature in kelvin is gonna be negative 1 96 degrees Celsius Plus to 73.15. And what you're gonna get is you're gonna get 77. kelvin. Notice how this is a positive number and we should always get positive numbers for kelvin. You can never have something that's negative kelvin, right? Because the lowest temperature is absolute zero. Alright, so negative 1 86 is actually 77.15 kelvin's and that's the answer to part A So now let's take a look at the second one. Now we want to convert negative 1 96 2. Fahrenheit. So we can have Celsius to Fahrenheit. So now we're just basically gonna use this equation over here, were given Celsius asked for Faron heights. So this is gonna be T. F. Equals 9/5 TC plus 32. So this is gonna be T. F equals 9/5. Uh This is gonna be let's see uh negative 1 96 plus 32. And what you're gonna get here is you're gonna get negative 320.8 degrees Fahrenheit. All right, so that's the answer to that one. No one really minor point just in case your professor super picky about this whenever you're expressing a temperature in Fahrenheit, you're always going to be right degrees Fahrenheit, anytime you're representing something in kelvin, you don't have to put the degree simple, you just write K. It's just kelvin's alright. That's it for this one. Guys, let me know if you have any questions.