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A student wants to construct a 4.7 uF capacitor out of two square plates for a science fair project.
He plans to use a paper dielectric (e,=2.5) that is 0.08 mm thick. What would be the size of the plates he need?


Sagot :

Answer:

To find the size of the plates needed to construct a 4.7 µF capacitor with a paper dielectric, we can use the formula for the capacitance of a parallel plate capacitor:

\[ C = \frac{\varepsilon_r \varepsilon_0 A}{d} \]

Where:

- \( C \) is the capacitance (4.7 µF or \( 4.7 \times 10^{-6} \) F)

- \( \varepsilon_r \) is the relative permittivity of the dielectric material (2.5 for paper)

- \( \varepsilon_0 \) is the permittivity of free space (\( 8.854 \times 10^{-12} \) F/m)

- \( A \) is the area of one of the plates

- \( d \) is the separation between the plates (0.08 mm or \( 0.08 \times 10^{-3} \) m)

First, rearrange the formula to solve for \( A \):

\[ A = \frac{C \cdot d}{\varepsilon_r \varepsilon_0} \]

Substitute the known values into the formula:

\[ A = \frac{4.7 \times 10^{-6} \, \text{F} \times 0.08 \times 10^{-3} \, \text{m}}{2.5 \times 8.854 \times 10^{-12} \, \text{F/m}} \]

Now calculate the area \( A \):

\[ A = \frac{4.7 \times 10^{-6} \times 0.08 \times 10^{-3}}{2.5 \times 8.854 \times 10^{-12}} \]

\[ A = \frac{3.76 \times 10^{-10}}{2.2135 \times 10^{-11}} \]

\[ A \approx 17.0 \, \text{m}^2 \]

This is the area of one plate in square meters. To find the side length \( L \) of the square plates, take the square root of the area:

\[ L = \sqrt{A} \]

\[ L = \sqrt{17.0} \]

\[ L \approx 4.12 \, \text{m} \]

Therefore, the student would need square plates approximately 4.12 meters on each side. This is quite large for a practical science fair project, and it might be worth considering alternative configurations or materials.