So in this problem, the radius off a tungsten wire is Europe wins or a 75 millimeter and is heated from the temperature. Tina equals 20 degrees Celsius to a temperature that is 13 20 degrees Celsius, which is t. The temperature coefficient of restive ity of the tungsten wire is 4.5 times 10 to the negative three degrees Celsius. Now it is also given that at temperature 13 20 degrees Celsius. When the vault is 100 and 20 volts is applied to the end of the wires. The current generated waas 1.5 amps. Now from here, we want to find the length of the wire. All right, so the first thing that we need to do is we need to find the registers of the wire at 13 to 20 degrees Celsius. And we used that resistance the value of resistance in Equation 20.5 from the text book to find the value of residence at 20 degrees Celsius and then using the relation between the resistance and resistive ity. Eventually we're gonna be able to find the length of the wire. All right, so let's begin. So we use home slop homes. Law is going to give us r equals few over I All right, and V is 1 20 1 20 volt over 1.5 Abbs. And this is going to give me a t o. Okay. No. Again. Like I said, Equation 20.5. Now what we do here, we plug in the value of our in this equation 20.5, Ana one plus alpha T minus. Tina from here are not the cause are over one plus all far, Teammate. Is Tina okay? And are we know it is 80 old? Let's go to the next place about that. So, huh are not is going to be, huh? Which is? I'm just gonna rewrite it again. Are over one plus alpha T minus Tina. And this is going to be 80 or over one. Plus Alfa is 4.5 times 10 to the negative. Three o meter and the temperature difference. 13. 20 bigger associates, minus 20 degrees Celsius. Okay, so from here, we're going to get 11.68 home. That is the resistance at 20 years old. Just now we know from the table 20.1. That resistive ity of tungsten at 20 degrees Celsius is 5.6 times 10 to the negative aid O meter. All right, so from the relation between resistance and resistive ity we can write down are not at 20 degrees Celsius are not because our omega hell over a Now, here's the thing. We don't know a CZ, but we are given the diamond there. Is it radius of the wire. So But we're gonna do here for us is we're going to write in terms of length. Okay, l The calls are not a over her omega. So but no e, which is the cross section of the wire is pie radius of the wire square, which is going to be pie, Which 3.141416 and radius was 7.5 times 10 to the negative five meter squared. And this is going to give me 1.77 times 10 to the negative. Eight meter squared. Okay, Now, we're gonna going to plug this value off a into this equation over here. Let's do that in next piece Real. Write it again. Elli. Cause are not a over Perot off home. A GE which is tungsten alright and are not Waas 11.68 home 0.68 home times. The area that we found was 1.77 times 10 to the negative eight meters squared over 5.6 times tend to the negative eight o meter and this is going to give me 3.69 meters.