Book cover for Physics

Physics

John D. Cutnell, Kenneth W. Johnson, David Young, Shane Stadler

ISBN #9781118486894

10th Edition

2,562 Questions

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Summary
Learning Objectives
Key Concepts
Example Problems
Explanations
Common Mistakes

Summary

This section introduces electric potential energy and electric potential, drawing a strong analogy to gravitational potential energy. Key equations such as V = kQ/r for point charges and EPE = qV for energy calculations are presented, along with the importance of equipotential surfaces in understanding the distribution of the electric field. Capacitors and several practical applications—ranging from copying machines to biomedical diagnostics—exemplify how these abstract concepts are used in real-world technology.

Learning Objectives

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Key Concepts

CONCEPT

DEFINITION

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Example Problems

Example 1

ssm Iron atoms have been detected in the sun's outer atmosphere, some with many of their electrons stripped away. What is the net electric charge (in coulombs) of an iron atom with 26 protons and 7 electrons? Be sure to include the algebraic sign $(+$ or $-$ ) in your answer.

Example 2

An object has a charge of $-2.0 \mu$ C. How many electrons must be removed so that the charge becomes $+3.0 \mu \mathrm{C} ?$

Example 3

Four identical metallic objects carry the following charges: +1.6 $+6.2,-4.8,$ and $-9.4 \mu \mathrm{C} .$ The objects are brought simultaneously into contact, so that each touches the others. Then they are separated. (a) What is the final charge on each object? (b) How many electrons (or protons) make up the final charge on each object?

Example 4

Four identical metal spheres have charges of $q_{\mathrm{A}}=-8.0 \mu \mathrm{C}$, $q_{\mathrm{B}}=-2.0 \mu \mathrm{C}, q_{\mathrm{C}}=+5.0 \mu \mathrm{C},$ and $q_{\mathrm{D}}=+12.0 \mu \mathrm{C}$ (a) Two of the spheres are brought together so they touch, and then they are separated. Which spheres are they, if the final charge on each one is $+5.0 \mu \mathrm{C} ?$ (b) In a similar manner, which three spheres are brought together and then separated, if the final charge on each of the three is $+3.0 \mu \mathrm{C} ?(\mathrm{c})$ The final charge on each of the three separated spheres in part (b) is $+3.0 \mu \mathrm{C}$. How many electrons would have to be added to one of these spheres to make it electrically neutral?

Example 5

ssm Consider three identical metal spheres, A, B, and C. Sphere A carries a charge of $+5 q .$ Sphere $\mathrm{B}$ carries a charge of $-q .$ Sphere $\mathrm{C}$ carries no net charge. Spheres $A$ and $B$ are touched together and then separated. Sphere $C$ is then touched to sphere $A$ and separated from it. Last, sphere $C$ is touched to sphere $\mathrm{B}$ and separated from it. (a) How much charge ends up on sphere $\mathrm{C} ?$ What is the total charge on the three spheres (b) before they are allowed to touch each other and (c) after they have touched?
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Step-by-Step Explanations

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