# The bar rides on parallel metal rails connected

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shown. The bar rides on parallel metal rails connected through a resistance R 0 so the apparatus makes a complete circuit. You can ignore the resistance of the bar and the rails. (a) (10 points) Find the direction of the current induced in the circuit using (i) Lenz’s Law; The magnetic flux through the loop is increasing into the paper. So the induced current must oppose this change by producing a new magnetic field out of the paper. So, by the Right Hand Rule, the current runs counterclockwise (and the induced emf runs counterclockwise). (ii) Motional emf. An electron inside the metal bar is moving to the right in a magnetic field. So it will be acted upon by a force 𝐹 𝐵 = 𝑞𝑣 × 𝐵 �⃗ = ( −𝑒 )( 𝜈 0 𝐵 0 sin 90 ° 𝚤̂ ) = 𝑒𝜈 0 𝐵 0 So the electron in the bar will travel to the bottom of the rod, leaving the top more positive. So the top of the bar is at a higher potential than the bottom, so the current in the outer circuit will flow counterclockwise. L 0 v 0 R 0 B 0 Page 22 of 31