A loop of wire of radius a = 35 has an electrical resistance R = 0.034ohm . The

Question

A loop of wire of radius a = 35 has an electrical resistance R = 0.034ohm . The loop is initially inside a uniform magnetic field of magnitude Binitial = 1.9 parallel to the loop's axis. The magnetic field is then reduced slowly at a constant rate, which induces a current I= 0.20A in the loop. How long does it take for the magnitude of the uniform magnetic field to drop from 1.9T to zero?As the external magnetic field decreases, an induced current flows in the coil. What is the direction of the induced magnetic field caused by this current? As the external magnetic field decreases, an induced current flows in the coil. What is the direction of the induced magnetic field caused by this current?

Explanation / Answer

induced EMF=-N*change in flux/time.

=-N*A*change in magnetic field/change in time

=-Pi*r^2*(B2-B1)/t = 3.14*0.35^2*19/t

EMF=0.731/t

So current=EMF/R

0.2=0.731/t*.034

t=107.5 sec

When this flux is decreased or increased, the current(charges) in the wire/coil/loop will move in such a direction that it will create it's own magnetic field (and therefore it's own magnetic flux) which will oppose the CHANGE in flux from the external magnet.

So.we wil find the direction of current using the above.

now using Thumb rule we can find the direction of magnetic field induced by the current

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