CBSE Class 12-science Answered
Hello
In motional emf q.wen there is rec loop placed in B ...and arm pq moves ..if velocity is towards right then v is positive and neg on left ?is it right ??so in case of right velocity ...emf is blv and not -blv right ?
Asked by jain.pradeep | 21 Feb, 2019, 10:01: PM
Expert Answer
I guess your doubt is about the direction of induced current, when a rectangular loop is moved in magnetic field.
Basically the direction of induced current is decided as per Lenz's law as explained in the figure given below.
As shown in figure(a), when north pole of magnet approaches the coil, magnetic flux increases.
As per faraday's law of induction, induced emf ξ = - (dφ/dt) , where φ is magenetic flux, induced emf is -ve because (dφ/dt) is +ve.
As per lenz's law, since induced emf opposes the motion of magnet, induced current flows in anticlockwise directionas shown in figure (a)
Similarly when north pole of magnet moves away from coil, magnetic flux decreases , induced current flows in clockwise direction.
Hence when magnetic flux increases, then induced current flows in anti clockwise direction in the coil
when magnetic flux decreases, then induced current flows in clockwise direction in coil
Now we see the situtaion when the coil is moving in magnetic field as explained by the figure below
Consider the case of loop-a and loop-b moving towards magnetic field, since magnetic flux increases,
current is flowing in anticlockwise direction as shown by red arrow
In case of loop-C and D , since magnetic flux decreases, current is flowing in clockwise direction.
When there is a relative motion between loop and magnetic field, we need to see whether magnetic flux increasing or decreasing .
Direction of incuced emf is decided as per the sign of change of magnetic flux
We need to remember -ve sign also appearing in faradays law of induction.
Hence as per the sign of change of magnetic flux , sign of induced emf is decided
Answered by Thiyagarajan K | 22 Feb, 2019, 05:23: PM
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