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A parallel-plate capacitor is charged and then disconnected from the battery, so that the charge Q on its plates cant change. Originally the separation between the plates of the capacitor is d and the electrical field between the plates of the capacitor is E = 6.0 × 10^4 N/C If the plates are moved closer together, so that their separation is halved and becomes d/2, what then is the electrical field between the plates of the capacitor? What if the battery is left connected?

Respuesta :

Answer:

[tex] E_f = \frac{V}{\frac{d}{2}}= 2 \frac{V}{d}= 2* 6x10^4 \frac{N}{C} = 1.2x10^5 \frac{N}{C}[/tex]

Explanation:

For this case we know that the electric field is given by:

[tex] E= 6 x 10^4 \frac{N}{C}[/tex]

And we want to find the final electric field assuming that the separation is halved and becomes d/2.

For this case we can use the following two equations:

[tex] C = \epsilon_o \frac{A}{d} = \frac{Q}{V}[/tex]   (1)

[tex] E = \frac{\sigma}{\epsilon_o}[/tex]   (2)

Where Q represent the charge, V the voltage, d the distance, A the area.

We can rewrite the equation (2) like this:

[tex] E = \frac{\sigma}{\epsilon_o} = \frac{Q}{A \epsilon_o}[/tex]   (3)

And we can solve for Q from equation (1)like this:

[tex] Q = \frac{\epsilon_o A V}{d}[/tex]

And if we replace into equation (3) the previous result we got:

[tex] E = \frac{\epsilon_o A V}{A d \epsilon_o} = \frac{V}{d}[/tex]

And since the the electric field not change and the distance would be the half we have that the final electric field would be given by:

[tex] E_f = \frac{V}{\frac{d}{2}}= 2 \frac{V}{d}= 2* 6x10^4 \frac{N}{C} = 1.2x10^5 \frac{N}{C}[/tex]