A dielectric is inserted into a capacitor while the charge on it is kept constant. What happens to the potential difference and the stored energy?
The potential difference decreases and the stored energy increases
Both the potential difference and the stored energy increase
The potential difference increases and the stored energy decreases
Both the potential difference and the stored energy decrease
Both the potential difference and the stored energy remain the same
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Correct option is D)
When a dielectric is placed in an electric field then an internal electric field is produced in it due to polarisation of dielectric . This internal electric field inside the dielectric is in opposite direction of the field between plates of capacitor , as a result of this effective electric field between plates decreases , hence the potential difference between plates because ,
where Δr is the distance between plates , which is constant .
Now potential energy of a capacitor is given by ,
charge is given constant , therefore due to decrease in potential difference ΔV , potential energy U also decreases .
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