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Asked by arjunsah797 | 31 Mar, 2022, 07:08: AM
When copper ball enters in magnetic field region , induced current circulates along the surface of copper balls.

we know, from faradys law of induction,  induced EMF ξ = - dφ/dt

where φ = flux of magnetic field = B × A

where B is magnetic field flux density , and A is area of ball in magnetic field region

When copper balls enters magnetic field region , ξ = - dφ/dt = - B ( dA/dt )

In above expression for induced EMF , dA/dt is positive

Hence induced EMF ξ is negative , hence induced current flows in clockwise direction along the surface of the ball .

This clockwise induced current gives induced magnetic field in the direction into the page as shown in figure.

Hence there is a repulsive force between applied magnetic field and induced magnetic field .
This repulsive force acts against the vertical downward motion of the ball.

When copper balls exits magnetic field region , ξ = - dφ/dt = - B ( dA/dt )

In above expression for induced EMF , dA/dt is negative

Hence induced EMF ξ is positive , hence induced current flows in counterclockwise direction along the surface of the ball .

This counterclockwise induced current gives induced magnetic field in the direction out of page as shown in figure.

Hence there is a attractive force between applied magnetic field and induced magnetic field .
This attractive force acts against the vertical downward motion of the ball.

When the area of the ball is fully in magnetic field region, there will not be any electromagnetic induction.

Only when the ball enters into magnetic field or exit from magnetic field ,
there is change in flux , hence we have electromagnetic induction.

Due to electromagnetic induction, copper ball is experienced by force that opposes the vertical motion as explained above.

Hence the bcopper ball slows down and takes longer time to reach ground
Answered by Thiyagarajan K | 31 Mar, 2022, 10:08: AM

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