As shown in the figure, two parallel plate capacitors having equal plate area of 200cm2 are joined in such a way that a=b. The equivalent capacitance of the combination is x∈0F. The value of x is ______.
Answer: 5
Solution
The two joined inner plates form a conducting region of thickness c=1 mm inside a capacitor whose outer plates are separated by d=5 mm. A conducting region adds nothing to the effective separation, so the arrangement behaves as a single capacitor of gap d−c=4 mm. With plate area A=200×10−4 m2, C=d−cϵ0A=4×10−3ϵ0×200×10−4=5ϵ0. The value of x is 5.