# Electromagnetic induction and magnetic field (conducting rail problem)

Since we know the work done by a magnetic field is zero.now how does the magnetic field changes the kinetic energy of rod when it applies force BIL (where I is current at any instant)

moreover if we apply if we apply some external force which balances the magnetic force the work done by both force will be 0(their sum) ,however we know induced current flows in circuit due to motional emf of rod and energy is lost through resistance where does this energy come from?(since no work is done)

• This is hard to understand. Could you please use shorter sentences? Aug 7, 2018 at 18:20
• should i edit it ? did u understand its about conducting bars kept on parallel conducting rails Aug 7, 2018 at 18:24
• Yes, I understand the set-up, but you seem to be cramming many ideas into each sentence, and it isn't too clear exactly what you're asking. Aug 7, 2018 at 18:27
• well i tried to simplify it Aug 7, 2018 at 18:35
• You did well. Much clearer. Aug 7, 2018 at 21:37

No, it doesn't. Ponderomotive forces (or Laplace forces) act on the conductor and they can do work. The Lorentz force $q\mathbf v\times\mathbf B$ acts on the charge carriers and does no work on them. But these forces do not act on the conductor (wire, rod) directly. Other forces due to charge carriers act on the conductor, which together form the macroscopic force of magnitude $BIL$. This macroscopic force, of course, does work.