I have trouble understanding the direction of components of earth magnetic field in my book there is a question "A car is travelling northward at a speed of ......m/s the vertical component of earth magnetic field is 4.8T in that location if an emf is induced between sides of the car which side of the car will be positive driver side or passenger side?" Will if we take the direction of vertical component downward the direction of Fm will be left so driver's side will be positive but if I take it upward the passenger side will be positive how can we understand to take which direction for vertical component of earth magnetic field?
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$\begingroup$ Related? physics.stackexchange.com/q/387744 To answer the question you need to be told where on the Earth the car is. $\endgroup$– FarcherCommented Feb 21, 2018 at 11:41
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$\begingroup$ it is just stated that the car moves toward North $\endgroup$– ClairCommented Feb 21, 2018 at 12:19
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$\begingroup$ Then all you can do is give two answers one for the car in the northern hemisphere and another for the car in the Southern Hemisphere? $\endgroup$– FarcherCommented Feb 21, 2018 at 12:27
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It is difficult to give an exactly clarification to this post without seeing the whole text of the question verbatim. Talking about the Earth's magnetic field in terms this simple is quite oversimplified. You correctly note that there are two different answers to this question depending on whether you assume the Earth's vertical magnetic field component comes up out of the Earth or goes down in to the Earth. Looking at the real Earth's magnetic field, I'd say that either assumption is equally valid.
Sorry to give such a non-answer to your question, but you seem to have correctly identified a rather unresolvable flaw in the textbook's original question. If you are somehow allowed to do it, I might just assume that the "vertical" component points up (because physics problem authors tend to think this way) and then put a little commentary about this dilemma at the end of your problem.
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$\begingroup$ "A car is travelling at speed of 15m/s the vertical component of earth magnetic field is 4.8*10^(-5) in that location an emf of 1.5*10^(-3) is induced between sides of the car" this is the question but I don't think it might help me find the exact direction of vertical component of earth magnetic field $\endgroup$– ClairCommented Feb 22, 2018 at 8:09
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$\begingroup$ In answer section the positive side is said to be driver side it means the direction of vertical component of earth magnetic field is taken downward $\endgroup$– ClairCommented Feb 22, 2018 at 8:10