Question Video: Converting from Kelvin to Fahrenheit Physics • Second Year of Secondary School

Video Transcript

What is 400 kelvin in degrees Fahrenheit? Give your answer to the nearest degree Fahrenheit.

Let’s begin by recalling that although the kelvin is the base SI unit of temperature, in some places, Fahrenheit is the most commonly used temperature scale, and thus it’s good practice to convert between the two. To do this, let’s recall that a temperature in Fahrenheit equals nine-fifths times the temperature in kelvin minus 273 all plus 32. Also notice that this part of the formula here is precisely how we convert a temperature given in kelvin to degrees Celsius. So we could choose to convert from kelvin to Celsius and then to Fahrenheit.

But for now let’s get some practice doing the conversion all in one go by using just this formula up top. Now we know that 𝑇 subscript k, the value we’re starting with, equals 400 kelvin. So let’s go ahead and substitute this into the formula. And we have nine-fifths times 400 kelvin minus 273 plus 32. We can plug this expression into a calculator and get a result of 260.6 degrees Fahrenheit. Finally, rounding this to the nearest whole number, we found that 400 kelvin equals 261 degrees Fahrenheit.