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Ch 23: The Electric Field
Knight Calc - Physics for Scientists and Engineers 5th Edition
Knight Calc5th EditionPhysics for Scientists and EngineersISBN: 9780137344796Not the one you use?Change textbook
Chapter 23, Problem 11

Two 10-cm-long thin glass rods uniformly charged to +10 nC are placed side by side, 4.0 cm apart. What are the electric field strengths E1 to E3 at distances 1.0 cm, 2.0 cm, and 3.0 cm to the right of the rod on the left along the line connecting the midpoints of the two rods?

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1
Understand the problem: Two uniformly charged rods are placed parallel to each other, and we need to calculate the electric field strength at specific points along the line connecting their midpoints. The electric field due to a uniformly charged rod can be calculated using the formula for the electric field of a line charge.
Set up the electric field formula for a uniformly charged rod: The electric field at a point along the perpendicular bisector of a uniformly charged rod is given by: E = ( k λ ) ( 1 / r ) where k is Coulomb's constant, λ is the linear charge density (charge per unit length), and r is the distance from the rod to the point of interest.
Calculate the linear charge density λ for each rod: Since the rods are uniformly charged, the linear charge density is given by: λ = Q / L where Q is the total charge on the rod (+10 nC) and L is the length of the rod (10 cm).
Determine the net electric field at each point (1.0 cm, 2.0 cm, and 3.0 cm): The electric field at each point is the vector sum of the contributions from both rods. For the rod on the left, the electric field points away from the rod (positive charge), and for the rod on the right, the electric field also points away. Use the principle of superposition to calculate the net electric field at each distance.
Substitute the values into the formula and solve: For each distance (1.0 cm, 2.0 cm, and 3.0 cm), substitute the values of λ, r, and k into the electric field formula. Add the contributions from both rods, taking into account their directions. This will give the electric field strength at each specified point.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electric Field

The electric field is a vector field that represents the force exerted by an electric charge on other charges in its vicinity. It is defined as the force per unit charge and is measured in newtons per coulomb (N/C). The direction of the electric field is away from positive charges and towards negative charges, and its strength diminishes with distance from the charge.
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Superposition Principle

The superposition principle states that the total electric field created by multiple charges is the vector sum of the electric fields produced by each charge individually. This principle allows us to calculate the net electric field at a point by considering the contributions from each charge separately, which is essential when dealing with multiple charged objects, like the two rods in this scenario.
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Coulomb's Law

Coulomb's Law describes the force between two point charges and is given by the equation F = k * |q1 * q2| / r^2, where F is the force, k is Coulomb's constant, q1 and q2 are the magnitudes of the charges, and r is the distance between them. This law is fundamental for calculating the electric field generated by a charge, as the electric field can be derived from the force experienced by a test charge placed in the field.
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Related Practice
Textbook Question

Two 10-cm-diameter charged rings face each other, 20 cm apart. The left ring is charged to −20 nC and the right ring is charged to +20 nC. What is the force on a proton at the midpoint?

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Textbook Question

CALC A 12-cm-long thin rod has the nonuniform charge density λ(x)=(2.0nC/cm)ex/(6.0cm)\(\lambda\)(x)=(2.0\,\(\text{nC/cm}\))e^{-|x|/(6.0\,\(\text{cm}\))}, where x is measured from the center of the rod. What is the total charge on the rod? Hint: This exercise requires an integration. Think about how to handle the absolute value sign.

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A 10-cm-long thin glass rod uniformly charged to +10 nC and a 10-cm-long thin plastic rod uniformly charged to −10 nC are placed side by side, 4.0 cm apart. What are the electric field strengths E1 to E3 at distances 1.0 cm, 2.0 cm, and 3.0 cm from the glass rod along the line connecting the midpoints of the two rods?

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Textbook Question

A small glass bead charged to +6.0 nC is in the plane that bisects a thin, uniformly charged, 10-cm-long glass rod and is 4.0 cm from the rod's center. The bead is repelled from the rod with a force of 840 μN. What is the total charge on the rod?

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Textbook Question

Two 10-cm-diameter charged rings face each other, 20 cm apart. The left ring is charged to −20 nC and the right ring is charged to +20 nC. What is the electric field Ē, both magnitude and direction, at the midpoint between the two rings?

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Textbook Question

An electret is similar to a magnet, but rather than being permanently magnetized, it has a permanent electric dipole moment. Suppose a small electret with electric dipole moment 1.0×10−7 C m is 25 cm from a small ball charged to +25 nC, with the ball on the axis of the electric dipole. What is the magnitude of the electric force on the ball?

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