Math Problem Statement

A parallel-plate capacitor is formed from two 6.0-cm-diameter electrodes spaced 2.0 mm apart. The electric field strength inside the capacitor is 1.0 × 106 N/C. What is the charge (in nC) on each electrode?

Solution

To find the charge on each electrode of the parallel-plate capacitor, we can use the relationship between the electric field EE, the charge QQ, the area AA of the plates, and the permittivity of free space ε0\varepsilon_0:

E=QAε0E = \frac{Q}{A \cdot \varepsilon_0}

Where:

  • EE is the electric field strength (1.0 × 10^6 N/C).
  • AA is the area of one of the electrodes.
  • ε0\varepsilon_0 is the permittivity of free space, approximately 8.85×1012F/m8.85 \times 10^{-12} \, \text{F/m}.

First, we need to calculate the area AA of one electrode, which is circular:

A=πr2A = \pi r^2

The radius rr can be found from the diameter:

r=6.0cm2=3.0cm=0.03mr = \frac{6.0 \, \text{cm}}{2} = 3.0 \, \text{cm} = 0.03 \, \text{m}

Now we calculate the area:

A=π(0.03m)22.827×103m2A = \pi (0.03 \, \text{m})^2 \approx 2.827 \times 10^{-3} \, \text{m}^2

Now we can rearrange the equation for charge QQ:

Q=EAε0Q = E \cdot A \cdot \varepsilon_0

Substituting the known values:

Q=(1.0×106N/C)(2.827×103m2)(8.85×1012F/m)Q = (1.0 \times 10^6 \, \text{N/C}) \cdot (2.827 \times 10^{-3} \, \text{m}^2) \cdot (8.85 \times 10^{-12} \, \text{F/m})

Calculating QQ:

Q(1.0×106)(2.827×103)(8.85×1012)2.5×1018CQ \approx (1.0 \times 10^6) \cdot (2.827 \times 10^{-3}) \cdot (8.85 \times 10^{-12}) \approx 2.5 \times 10^{-18} \, \text{C}

Now converting this charge into nanocoulombs (nC):

Q2.5×1018C×109nC/C2.5×109nC2.5nCQ \approx 2.5 \times 10^{-18} \, \text{C} \times 10^{9} \, \text{nC/C} \approx 2.5 \times 10^{-9} \, \text{nC} \approx 2.5 \, \text{nC}

Thus, the charge on each electrode is approximately 2.5 nC.

If you have any questions or need further details, feel free to ask! Here are some related questions you might consider:

  1. How does the capacitance change if the distance between the plates is increased?
  2. What factors influence the electric field strength in a capacitor?
  3. How would the charge on the plates change if the diameter of the electrodes was doubled?
  4. What is the relationship between capacitance, voltage, and charge in a capacitor?
  5. How does introducing a dielectric material affect the charge and electric field in the capacitor?

Tip: Remember to always keep track of units when performing calculations in physics!

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Math Problem Analysis

Mathematical Concepts

Electrostatics
Capacitance
Geometry

Formulas

E = Q / (A * ε₀)
A = πr²
Q = E * A * ε₀

Theorems

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Suitable Grade Level

Grades 11-12