dielectric slab attraction

Sep 2009
409
155
india
In many problems, i see a dielectric goes in or out of capacitorr plates.i do not understand clearly why a dielectric gets attracted. if someone knows the mechanism, please tell me.
 

werehk

PHF Hall of Fame
Apr 2008
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Mechanism is simple. For a dielectric and a negatively charged rod near it, the molecules inside would be polarized and arranged in a manner such that the positive poles induced on the molecules would be pointing towards the negatively charged rod.
 
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Sep 2009
409
155
india
exactly this is where i got stuck.the forces on the dielectric slab will be in vertical direction . how are we getting the horizontal component needed for attraction into the plates?
 

werehk

PHF Hall of Fame
Apr 2008
886
180
HK
Dielectrics


From the image, we see that positive charges on metal plate and negative poles of dielectric are closer than that of positive charges on metal plate and positive poles of dielectric. As a result, the attraction force is greater than that of repulsion force as electric forces obey inverse square law. Therefore there is a net attraction between parallel plate and dielectric.