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Consider a thin spherical shell of radius \(14.0 \mathrm{cm}\) with a total charge of \(32.0 \mu \mathrm{C}\) distributed uniformly on its surface. Find the electric field (a) \(10.0 \mathrm{cm}\) and (b) \(20.0 \mathrm{cm}\) from the center of the charge distribution.

Short Answer

Expert verified
The electric field \(10.0 \mathrm{cm}\) from the center of the distribution is \(0 \mathrm{N/C}\), since we are inside the sphere. The electric field \(20.0 \mathrm{cm}\) from the center of the distribution can be calculated using the formula defined in Step 4.

Step by step solution

01

Defining the problem using Gauss' theorem

Gauss' Law states that the electric flux through a closed surface is equal to the charge enclosed by that surface divided by the permittivity of free space. Since our surface is a sphere, and considering its symmetry, the electrical field \(E\) is constant in magnitude at every point on its surface. Therefore the total electric flux through the surface is equal to \(E\) times the total surface area.
02

Find the electric field inside the sphere

When the distance from the center of the sphere is less than its radius (i.e., we are within the sphere), there is no charge enclosed by the surface. Therefore, according to Gauss' Law, the electric field inside the sphere must be zero.
03

Find the electric field outside the sphere

When the distance from the center of the sphere is greater than its radius (i.e., we are outside the sphere), the flux through our surface equals the total charge \(Q\) divided by the permittivity of free space. Therefore, by Gauss' Law, the electric field \(E = Q / (4πε_0 r^2)\), where \(r\) is the distance from the center of the sphere and \(ε_0\) is the permittivity of free space, a constant approximately equal to \(8.85 x 10^{-12} \mathrm{C}^2/\mathrm{N} \cdot \mathrm{m}^2\).
04

Apply the obtained formula to the specific distances

The electric field \(10.0 \mathrm{cm}\) from the center of the distribution is \(E = Q / (4πε_0 r^2)\), with \(Q = 32 \mu C\) and \(r = 10 \mathrm{cm}\). Therefore, using the given values and converting the units appropriately, we get \(E = 32.0 \mu C / (4π(8.85 x 10^{-12} \mathrm{C}^2/\mathrm{N} \cdot \mathrm{m}^2)(0.10 \mathrm{m})^2)\). Likewise, for the distance \(20.0 \mathrm{cm}\) from the center of the charge distribution, we repeat the calculation with \(r = 20 \mathrm{cm}\).

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Electric Field
The electric field is a fundamental concept in electrostatics, describing the force exerted per unit charge at any given point in space. It is represented by the vector field \(\mathbf{E}\), which points in the direction of the force that a positive test charge would experience. The strength of the electric field is typically measured in newtons per coulomb (\(\mathrm{N/C}\)) or volts per meter (\(\mathrm{V/m}\)).

Gauss' Law provides a powerful tool for calculating the electric field produced by symmetric charge distributions. This law asserts that the electric flux through a closed surface is equal to the charge enclosed by that surface over the permittivity of free space, given by \(\epsilon_0 \approx 8.85 \times 10^{-12} \mathrm{C}^2/\mathrm{N} \cdot \mathrm{m}^2\). This simplifies the calculation of electric fields, particularly for spherical or cylindrical symmetry.

When considering a spherical shell as in our problem, the electric field behaves differently inside and outside the shell. Inside the spherical shell, no electric field is present because there's no net enclosed charge. Outside the shell, the electric field behaves as if the entire charge were concentrated at the center of the sphere, allowing us to calculate it using the formula \(E = \frac{Q}{4\pi\epsilon_0 r^2}\), where \(Q\) is the total charge and \(r\) is the radial distance from the center.
Spherical Shell
A spherical shell is a three-dimensional structure that looks like a hollow ball. In this configuration, we focus on a thin shell, meaning it has negligible thickness compared to its radius. The charge is uniformly distributed across its surface, which greatly affects how we apply Gauss' Law.

The problem involves determining the electric field at specific points related to this spherical shell. Key distances include those less than, equal to, and greater than the shell's radius. For any point inside the shell, the enclosed charge is zero, resulting in a zero electric field due to the symmetry of the charge distribution across the shell's surface. This confirms that electric fields cancel each other inside such a spherical distribution.

Outside the shell, the entire charge distribution can be imagined as a point charge at the center of the shell. This approach, enabled by Gauss' Law, simplifies the calculation of the electric field at any point outside the shell because we use the charges' total amount, \(Q = 32.0 \mu \mathrm{C}\), and the distance from the center to point \(r\) in our equation \(E = \frac{Q}{4\pi\epsilon_0 r^2}\).

Recognizing the sphere's symmetry allows a simpler analysis and application of electrostatic principles.
Charge Distribution
The spherical shell in the exercise has a total charge of \(32.0 \mu \mathrm{C}\) distributed uniformly on its surface. Understanding this type of charge distribution is crucial for analyzing its electric field effects.

Uniform distribution means each part of the shell's surface holds an equal portion of the total charge. This implies that any point on the surface is essentially indistinguishable from any other point in terms of charge density, leading to uniform electric field values at any equidistant external point from the shell.

Such symmetry allows a straightforward application of Gauss' Law. The spherical symmetry ensures that, internally, no net electric field builds up because any surface inside encloses zero net charge. Outside the shell, the entire charge acts as though concentrated at the center, simplifying field calculations.

This concept underpins many electrostatic problems where uniform spherical charge distributions are involved, illustrating how symmetry and law work together to simplify complex system analyses.

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Most popular questions from this chapter

A point charge of \(12.0 \mu \mathrm{C}\) is placed at the center of a spherical shell of radius \(22.0 \mathrm{cm} .\) What is the total electric flux through (a) the surface of the shell and (b) any hemispherical surface of the shell? (c) Do the results depend on the radius? Explain.

A cylindrical shell of radius \(7.00 \mathrm{cm}\) and length \(240 \mathrm{cm}\) has its charge uniformly distributed on its curved surface. The magnitude of the electric field at a point \(19.0 \mathrm{cm}\) radially outward from its axis (measured from the midpoint of the shell) is \(36.0 \mathrm{kN} / \mathrm{C} .\) Find (a) the net charge on the shell and (b) the electric field at a point \(4.00 \mathrm{cm}\) from the axis, measured radially outward from the midpoint of the shell.

A positive point charge is at a distance \(R / 2\) from the center of an uncharged thin conducting spherical shell of radius R. Sketch the electric field lines set up by this arrangement both inside and outside the shell.

A solid sphere of radius \(40.0 \mathrm{cm}\) has a total positive charge of \(26.0 \mu \mathrm{C}\) uniformly distributed throughout its volume. Calculate the magnitude of the electric field (a) \(0 \mathrm{cm}.\) (b) \(10.0 \mathrm{cm},\) (c) \(40.0 \mathrm{cm},\) and \((\mathrm{d}) 60.0 \mathrm{cm}\) from the center of the sphere.

A particle with a charge of \(-60.0 \mathrm{nC}\) is placed at the center of a nonconducting spherical shell of inner radius \(20.0 \mathrm{cm}\) and outer radius \(25.0 \mathrm{cm} .\) The spherical shell carries charge with a uniform density of \(-1.33 \mu \mathrm{C} / \mathrm{m}^{3}.\) A proton moves in a circular orbit just outside the spherical shell. Calculate the speed of the proton.

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