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Define motional emf and derive an expression for it.

Define motional emf and derive an expression for it.

Grade:Upto college level

4 Answers

Apoorva Arora IIT Roorkee
askIITians Faculty 181 Points
6 years ago
When a conductor is moved across a magnetic field, a potential difference is setup across its ends.
This potential difference is called'motional EMF'.
Consider a wire of length "L" moving across the magnetic field of inductionBwith a velocityvas shown in diagram.
237-2343_emf.jpg
Each free electron of the wire is moving within the wire and experience a force exerted by magnetic field.
F=q(v\times B)
here q=-e
F=-e(v\times B)
F=e(B\times v)
These electrons gradually accumulate at the end "a" and leaving the other end "b".In this way point "b" acquires positive charge and point "a" acquires equal negative charge.
This accumulation of electrons will continue till the force of electric field balances the force due to the motion of wire. Thus a potential difference is setup form pointbto pointa.
We know
Potential Difference = work done per unit charge
Let the total charge flows through the wire is "q" therefore
P.D.=work/charge
P.D.=F.d/q
P.D.=e(B\times v)L/e
P.D.=L(B\times v)
or
P.D.=BvLsin\theta
This is called motional EMF.
Thanks and Regards
Apoorva Arora
IIT Roorkee
askIITians Faculty
NIKHIL
15 Points
2 years ago
dfi=B.dA
     =B.I.V.dt
=> €= -dfi/dt
Therefore, €= -BIV
This emf is called motional emf.
Direction of induced current by Fleming's Right Hand Rule.
Aditya
13 Points
2 years ago
Consider a  rod moving in a magnetic field with a velocity v. We know that the rod is containing some free electrons which drift in the rod  towards an end due to magnetic force leading to charge seperated in the rod. Now we can see q(v×B)=qE hence we obtain expression for the induced electric field E = Bv now we now total emf developed in the rod  \int_{0}^{L}(E.dx) = BvL
ankit singh
askIITians Faculty 614 Points
8 months ago
Motional emf: When an conducting loop or rod moves in the in an uniform magnetic field, so that flux through the loop changes, due to the change in the flux through the loop, an emf is induced it the loop, which is called motional emf.

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