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the question image

I came across this question in an exam and there is an option to challenge the answers so please suggest me if my perspective is right or wrong? the answer is given to be the option (C) but I have chosen option (d) in the exam.

I don't understand exactly why he mentioned that the sign of emf will be negative when the loop is entering the field. I guess they did so because the formula for emf in a loop is E=-(rate of change of flux per time) and since the flux is increasing the emf should be more negative... but that approach is wrong because it never mentioned anything about the direction in which the emf causes the current.

Think of it this way, if the direction the filed is pointing outwards instead of into the paper(as given it the question) the direction of emf should be opposite to what it was before and so should be of +ve sign but as per the paper setters logic this seems to negative sign in this case also because field is increasing this time also. so, I feel both option c and d should be considered correct.

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  • $\begingroup$ I agree with you. No information or guidance was given in the question as to which direction of the EMF or current was to be regarded as being positive or negative. With the information given, all one can say is that either (C) or (D) is correct. $\endgroup$ – Samuel Weir Feb 28 '18 at 0:47
  • $\begingroup$ ya.. so ill be challenging the question so, is it okay if I put the same way I have put in the question exact words in my challenge or must I frame it in a better way? $\endgroup$ – dushyanth Feb 28 '18 at 0:53
  • $\begingroup$ I would just keep it short and to the point: There is neither any information in the question nor any standard convention for which direction of the EMF or current is positive or negative in the loop shown. In the absence of such information, either answer (C) or answer (D) could be correct. $\endgroup$ – Samuel Weir Feb 28 '18 at 1:05
  • $\begingroup$ That seems to be precisely to the actual point and succinct. Thank you very much. $\endgroup$ – dushyanth Feb 28 '18 at 1:47

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