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A parallel-plate capacitor is constructed of two square plates, size L x L, separated by distance d. The plates are given charge ±Q.
a. What is the ratio Ef/Ei of the final to initial electric field strengths if L is doubled?

Answer :

Answer:

Explanation:

Given

Area of capacitor Plates [tex]A=L\times L[/tex]

distance between plates is d

capacitance C is given by

[tex]C=\frac{\epsilon A}{d}[/tex]

[tex]C=\frac{\epsilon \cdot L^2}{d}[/tex]

Provided V is Voltage

[tex]Charge(Q)=capacitance(C)\times Voltage(V)[/tex]

If L is doubled

Capacitance [tex]C'=\frac{\epsilon \cdot (2L)^2}{d}[/tex]

[tex]C'=4\times \frac{\epsilon \cdot L^2}{d}[/tex]

Electric field is given by

[tex]E=\frac{Q}{\epsilon _0A}[/tex]

[tex]E_i=\frac{Q}{\epsilon _0L^2}---1[/tex]

[tex]E_f=\frac{Q}{\epsilon _0(2L)^2}---2[/tex]

divide 1 and 2 we get

[tex]\frac{E_i}{E_f}=\frac{(2L)^2}{L^2}[/tex]

[tex]\frac{E_f}{E_i}=\frac}{1}{4}[/tex]

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