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Ch 26: Potential and 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 26, Problem 3

FIGURE EX26.3 is a graph of Ex. What is the potential difference between xi=1.0 m and xf=3.0 m?
Graph of electric field Ex in volts per meter versus position x in meters, showing a linear increase from -200 to 400 V/m.

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1
Identify the relationship between the electric field \( E_x \) and the potential difference \( \Delta V \). The potential difference is given by the integral of the electric field along the path: \( \Delta V = - \int_{x_i}^{x_f} E_x \, dx \).
From the graph provided (FIGURE EX26.3), observe the values of \( E_x \) as a function of \( x \) between \( x_i = 1.0 \; \text{m} \) and \( x_f = 3.0 \; \text{m} \). Note whether \( E_x \) is constant, linear, or varies in another way.
If \( E_x \) is constant over a segment, the integral simplifies to \( \Delta V = -E_x \cdot (x_f - x_i) \). If \( E_x \) varies, divide the interval into smaller segments where \( E_x \) is approximately constant or use the functional form of \( E_x \) to compute the integral.
Evaluate the integral \( \int_{x_i}^{x_f} E_x \, dx \) using the graph. For example, calculate the area under the curve (taking into account the sign of \( E_x \)) between \( x_i = 1.0 \; \text{m} \) and \( x_f = 3.0 \; \text{m} \).
Substitute the result of the integral into \( \Delta V = - \int_{x_i}^{x_f} E_x \, dx \) to find the potential difference. Ensure the correct sign is applied based on the direction of the electric field.

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Key Concepts

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

Electric Field (E)

The electric field (E) is a vector field that represents the force per unit charge experienced by a positive test charge placed in the field. It is defined as the gradient of the electric potential (V) and is measured in volts per meter (V/m). Understanding the electric field is crucial for determining how charges interact and how potential differences arise in a given region.
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Electric Potential (V)

Electric potential (V) is the amount of electric potential energy per unit charge at a specific point in an electric field. It is measured in volts (V) and indicates the work done to move a charge from a reference point to the specified point without any acceleration. The difference in electric potential between two points is what drives the movement of charges, leading to current flow in circuits.
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Potential Difference (ΔV)

Potential difference (ΔV) is the difference in electric potential between two points in an electric field, calculated as ΔV = V_final - V_initial. It represents the work done per unit charge in moving a charge between these two points. In the context of the question, calculating the potential difference between xi=1.0 m and xf=3.0 m involves integrating the electric field over that distance to find the total change in potential.
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