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Q6.14 (d) Figure 6.20 shows a metal rod PQ  resting on the smooth rails AB and positioned between the poles of a  permanent magnet. The rails, the rod, and the magnetic field are in three mutual perpendicular directions. A galvanometer G connects the rails through a switch K. Length of the rod=15cmB=0.50T, resistance of the closed loop containing the rod=9.0m\Omega . Assume the field to be uniform. Suppose K is open and the rod is moved with a speed of 12cm\: s^{-1} in the direction shown. Give the polarity and magnitude of the induced emf.What is the retarding force on the rod when K is closed?

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The formula to calculate the force on the conductor moving in a magnetic field is,

F=Bil

Where,

 i is the induced current.

 B is the magnetic field strength.

 l is the length of the conductor.

The induced current is calculated as,

I=e/R =\frac{9\times10^{-3}}{9\times10^{-3}}= 1A

The length of the rod is 0.15 m.

Magnetic field strength, B=0.50 T.

Substitute the value in the above formula,

F=Bil =1\times 0.5\times 0.15 =75\times 10^{-3} N

Hence, the retarding force on the rod is 75× 10 −3  N.

Posted by

Pankaj Sanodiya

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