# Al-Physics E-field (concept)

When there have a parallel plate capacitor,

For case 1

There have a dielcetric substance between the plates

Case 2,

There is vaccum between the plates.

Question:

Why the E-field between the plates in case 1 is less than case 2(magnitude)?

Please don't explain by any formula but in theoredical word form.

### 1 個解答

• 天同
Lv 7
10 年前
最愛解答

In simple terms, when there are charges on the plates, these charges will induce charges on the upper and lower side of the dielectric slab. If the upper plate is +ve charged, then -ve charge will be induced on the upper side of the slab. Similarly, the lower side of the slab will be induced +ve charge by the -ve charge on the lower plate.

As you can see that the electric field set up by the induced charges on the dielectric slab is upward, running from the lower side of the slab (which is +ve charged) to the upper side (which is -ve chraged). The field is in opposite direction to that produced by the charges on the plates, which is running dwownward. There is thus a "cancellation effect" of the two fields. Because the induced charges on the dielectric slab are smaller in magnitude than that of the charges residing on the plates, the field set up by the charged plates is stronger than the field produced by the induced chages. The result is that the original field (i.e. the field without the dielectric slab in place), is weakened by the presence of the dieelctric.