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Physics/Fleming Left Hand Rule Vs Right Hand Palm Rule


Right hand rule
Right hand rule  
Left hand rule
Left hand rule  
QUESTION: I am really confused about which method to use for finding direction of magnetic force experienced by a charged particle , because they give different results . In the LHR pic , if the direction of magnetic field is downwards (-ve y-axis) , & that of current is straight , we get direction of force according to LHR ,along +ve X-axis. However according to RHR , when the thumb points in the direction of current i.e straight , as in case of LHR , & fingers in the direction of magnetic field ,we get force along -ve X-axis i.e opposite to that of LHR .So am i going wrong somewhere or are these rules not same in all cases.

ANSWER: I have no idea what the top diagram is doing. The bottom diagram is correct. if you point the thumb of your right hand in the direction of motion of a POSITIVE charge while the fingers of your right hand points in the direction of the magnetic field, the palm of your right hand will point in the direction of the magnetic force. For example, if the positive particle is moving towards the right (+x) while your fingers are pointing down (-y), the palm of your right hand will be pointing into the page, away from you (-z).
Your first diagram looks like the technique used to determine the direction of the magnetic field in the vicinity of a long, straight current carrying conductor rather than for predicting force (in my opinion).

---------- FOLLOW-UP ----------

QUESTION: No , actually Ist diagram is recommended on my reference book , but i find it inaccurate and hard to do . The first technique is Fleming's Left Hand Rule , which is also used for finding the direction of magnetic force due to magnetic field.Here is the statement for Left hand rule given in my book, "IF we stretch the 1st finger , the central finger & the thumb of left hand mutually perpendicular to each other such that the first finger points to the direction of magnetic field, the central finger points to the direction of electric current(motion of positive charge), then the thumb represents the direction of force experienced by the charged particle."

Again, I am unfamiliar with your top diagram and have always used the right hand rule as in the lower diagram. You are correct in that the first diagram seems more confusing. It is easy to picture the fingers of the right hand as "magnetic field lines" and since we "push" with the palms or out hands remembering the meanings is much more straight forward.


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James J. Kovalcin


I am teaching or have taught AP physics B and C [calculus based mechanics & electricity and magnetism] as well as Lab Physics for college bound students. I have a BS in Physics from the University of Pittsburgh and a Master of Arts in Teaching from same. I have been teaching physics for 34 years. I am constantly updating my skills and have a particular interest in modern physics topics.

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