Applejuice Posted April 7, 2014 Posted April 7, 2014 The problem I have is the following: "A magnetar has a magnetic field of 1015G on its surface. Also, the radius of the magnetar is 10 kilometer. The magnetar is at the same distance from earth as the moon is. How far do you have to travel towards it to reach a magnetic field of 104G?" I have no idea how I would even approach this problem.... Can someone give me a push in the right direction? Any help would be much appreciated! Also, I'm new here. Please forgive me if I broke a rule.
swansont Posted April 7, 2014 Posted April 7, 2014 Do you have an equation that tells you field strength as a function of distance? 1
Applejuice Posted April 7, 2014 Author Posted April 7, 2014 Do you have an equation that tells you field strength as a function of distance? This is what I have been looking for. The only formula I could find that was from a seemingly reliable sources was I = 1/d2 , wherein I = intensity and d = distance. In other words, some people claim that it follows the inverse square law. This would be for a 'monopole', though. For a dipole it would be I = 1/d3. If this is true then it's easily solvable, but some sources tell me that it's not exactly true... Other than that, I don't exactly understand why magnetism follows the inverse square law, but that's for another day.
vampares Posted April 7, 2014 Posted April 7, 2014 (edited) This question is simple. Given the exact distance, this exact distance is the movement. Duh? If you tell me that we would reach the 104G prior to my ingenious inception, I would ask you to move the planet. You have to place a limit on these things. Besides, I think you probably wrote the "magnatar" wiki yourself. There is no such thing as a "magnatar". Edited April 7, 2014 by vampares
Applejuice Posted April 8, 2014 Author Posted April 8, 2014 This question is simple. Given the exact distance, this exact distance is the movement. Duh? If you tell me that we would reach the 104G prior to my ingenious inception, I would ask you to move the planet. You have to place a limit on these things. Besides, I think you probably wrote the "magnatar" wiki yourself. There is no such thing as a "magnatar". I can now see that the question is not too difficult, but I'm learning. I have not mentioned this "magnatar" you speak of. Please feel free to check out what I was actually talking about. http://en.m.wikipedia.org/wiki/Magnetar Although a bit offtopic, was it necessary write your post in this patronizing manner? I'm trying to learn new things here... 1
swansont Posted April 8, 2014 Posted April 8, 2014 This is what I have been looking for. The only formula I could find that was from a seemingly reliable sources was I = 1/d2 , wherein I = intensity and d = distance. In other words, some people claim that it follows the inverse square law. This would be for a 'monopole', though. For a dipole it would be I = 1/d3. If this is true then it's easily solvable, but some sources tell me that it's not exactly true... Other than that, I don't exactly understand why magnetism follows the inverse square law, but that's for another day. It would be the dipole equation, so it's not the inverse square. So you have the field strength at the surface and you know r for that. You should be able to set up a ratio and find the field strength at any distance.
CaptainPanic Posted April 8, 2014 Posted April 8, 2014 ! Moderator Note vampares, The tone of your post seems to suggest that the person asking the question should have understood this already (the "Duh" is often used to point that out). But this is the Homework section where people are supposed to be learning, and asking questions is a vital part of learning. Also, if you are going to reply that things do not exist, please check this first (and if your favorite search engine does not suggest an alternative spelling, please make sure you get it right when you check it). Do not reply to this mod tip in the thread. If you have any problems with it, use the report function at the bottom of this post.
Applejuice Posted April 8, 2014 Author Posted April 8, 2014 (edited) It would be the dipole equation, so it's not the inverse square. So you have the field strength at the surface and you know r for that. You should be able to set up a ratio and find the field strength at any distance. Forgive me if this is dense of me to ask, but how should I go about setting up a ratio? I only know the surface strength and the r. So 10km from center has 10^15G, but then what? I do not know the core strength or the strength at any other point. Any help would again be much appreciated! Edited April 8, 2014 by Applejuice
swansont Posted April 8, 2014 Posted April 8, 2014 Forgive me if this is dense of me to ask, but how should I go about setting up a ratio? I only knoe the surface strength and the r. So 10km fron center has 10^15G, but then what? I do not know the core strength or the strength at any other point. Any help would again be muxh appreciated! You know the strength at the point you want to reach: 104 G
Applejuice Posted April 8, 2014 Author Posted April 8, 2014 (edited) You know the strength at the point you want to reach: 104 G .... // Okay, so here's my attempt at solving it. Meaning that the field has a strength of 1018 at the core of the magnetar Setting up x for distance and the outcome to be 104 Am I doing this correctly? Edited April 8, 2014 by Applejuice
swansont Posted April 8, 2014 Posted April 8, 2014 Looks OK so far. But x isn't what the question is asking for, so you have one more step. 1
Applejuice Posted April 8, 2014 Author Posted April 8, 2014 (edited) Ah yes. The distance to the moon from earth on average is about 384400 km, so 384400-46415 = 337,985 km. Thanks again for all the help, I'm really grateful! Edited April 8, 2014 by Applejuice
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