# In which of the above figures will the light bulb be glowing?

What is principle of solution behind this induction problem (problem 29)? The problem can be find in here (problem 29).

Problem is: The five separate figures below involve a cylindrical magnet and a tiny light bulb connected to the ends of a loop of copper wire. These figures are to be used in following question. The plane of the wire loop is perpendicular to the reference axis. The states of motion of the magnet and of the loop of wire are indicated in the diagram. Speed will be represented by v and CCV represent counter clockwise. (look at the picture in here( problem 29))

29) In which of the above figures will the light bulb be glowing?

(a) I, III, IV (b) I, IV (c) I, II, IV (d) IV (e) None of these.

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 Let me ask that how do you post pictures to the questions in this website? – alvoutila Nov 2 '12 at 14:13 If you click on the little square on the question tool bar it asks you for the url of the image to upload either from your computer or from the web. – anna v Nov 2 '12 at 14:28 I tried but it failed. It takes wrong link like; [3]: i.stack.imgur.com/2cO6y.png – alvoutila Nov 2 '12 at 14:49 Maybe you haven't noticed. It displays the image right now. And, that's not a wrong link. That's where you've uploaded the image through the link you've provided :-) – Ϛѓăʑɏ βµԂԃϔ Nov 2 '12 at 15:20

 Do you use formula " Faraday's law of induction states the induced electromotive force (EMF) in the wire is $E= - \frac{d \Phi_B}{dt}$ "? – alvoutila Nov 3 '12 at 11:10 @alvoutila: Yes, but carefully, because while the formula is true, it is due to two different effects (which are ultimately related by relativity)--- the Lorentz force law and the Faraday induction law, depending on whether it's the magnet or the wire that is moving. – Ron Maimon Nov 3 '12 at 13:45