A rod of length e has a uniform positive charge per unit length a and a total charge Q. Calculate the electric field at a point P that is located along the long axis of the rod and a distance a from one end (see figure). The electric field at P due to a uniformly charged rod lying along the ais. P SOLUTION Conceptualize The field dE at P due to each segment of charge on the rod is in the --Select- v x-direction because every segment carries a positive charge. The figure shows the appropriate geometry. In our result, we expect the electric field to become smaller as the distance a becomes larger because point P is farther from the charge distribution. Categorize Because the rod is continuous, we are evaluating the field due to a continuous charge distribution rather than a group of individual charges. Because every segment of the rod produces an electric field in the -Select-- v x-direction, the sum of their contributions can be handled without the need to add vectors. Analyze Let's assume the rod is lying along the x-axis, dx is the length of one small segment, and da is the charge on --Select- v Because the rod has a charge per unit length 2, the charge da on the small segment is da - i dx. Find the magnitude of the electric field at P due to one segment of the rod having a charge dg. (Use the following as necessary: a, k, 2, e, and x.) ) dx Find the total field at Pusing the equation for the electric field due to a continuous charge distribution: E- Noting that k and - are constants and can be removed from the integral, evaluate the integral. (Use the following as necessary: a, k, , and Q.) (1) E- k- Finalize We see that our prediction is correct; if a becomes larger, the denominator of the fraction grows larger, and E--Select- which the observation point Pis at zero distance from the charge at the end of the rod, so the field becomes infinite. On the other hand, if a-0, which corresponds to sliding the bar to the left until its left end is at the origin, then E-. That represents the condition in EXERCISE A rod 17.0 cm long is uniformly charged and has a total charge of -25.0 pc. Hint (a) Determine the magnitude of the electric field (in N/C) along the long axis of the rod at a point 37.0 cm from its center.

Physics for Scientists and Engineers
10th Edition
ISBN:9781337553278
Author:Raymond A. Serway, John W. Jewett
Publisher:Raymond A. Serway, John W. Jewett
Chapter23: Continuous Charge Distributions And Gauss's Law
Section: Chapter Questions
Problem 5P: Example 23.3 derives the exact expression for the electric field at a point on the axis of a...
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A rod of length e has a uniform positive charge per unit length A and a total charge Q. Calculate the electric field at a point P that is located along the long axis of the rod and a distance a from one end (see figure).
The electric field at P due to a uniformly charged rod lying along the x-axis.
dx
P
a
SOLUTION
Conceptualize The field dE at P due to each segment of charge on the rod is in the --Select-- v
because point P is farther from the charge distribution.
v x-direction because every segment carries a positive charge. The figure shows the appropriate geometry. In our result, we expect the electric field to become smaller as the distance a becomes larger
Categorize Because the rod is continuous, we are evaluating the field due to a continuous charge distribution rather than a group of individual charges. Because every segment of the rod produces an electric field in the -Select--- vy x-direction, the sum of their contributions can be handled
without the need to add vectors.
Analyze Let's assume the rod is lying along the x-axis, dx is the length of one small segment, and dg is the charge on --Select--- v
Because the rod has a charge per unit length a, the charge dg on the small segment is dg = a dx.
Find the magnitude of the electric field at P due to one segment of the rod having a charge dg. (Use the following as necessary: a, k, 1, e, and x.)
dx
da
dE = k
=
x²
Find the total field at P using the equation for the electric field due to a continuous charge distribution:
--?-- v
E =
Noting that k. and 1 = 2 are constants and can be removed from the integral, evaluate the integral. (Use the following as necessary: a, k, e, and Q.)
-7- v
-2-- v
E - kA
1
(1)
E =
Finalize We see that our prediction is correct; if a becomes larger, the denominator of the fraction grows larger, and E--Select-
. On the other hand, if a → 0, which corresponds to sliding the bar to the left until its left end is at the origin, then E - o. That represents the condition in
which the observation point Pis at zero distance from the charge at the end of the rod, so the field becomes infinite.
EXERCISE
A rod 17.0 cm long is uniformly charged and has a total charge of –25.0 µC.
Hint
(a) Determine the magnitude of the electric field (in N/C) along the long axis of the rod at a point 37.0 cm from its center.
Transcribed Image Text:A rod of length e has a uniform positive charge per unit length A and a total charge Q. Calculate the electric field at a point P that is located along the long axis of the rod and a distance a from one end (see figure). The electric field at P due to a uniformly charged rod lying along the x-axis. dx P a SOLUTION Conceptualize The field dE at P due to each segment of charge on the rod is in the --Select-- v because point P is farther from the charge distribution. v x-direction because every segment carries a positive charge. The figure shows the appropriate geometry. In our result, we expect the electric field to become smaller as the distance a becomes larger Categorize Because the rod is continuous, we are evaluating the field due to a continuous charge distribution rather than a group of individual charges. Because every segment of the rod produces an electric field in the -Select--- vy x-direction, the sum of their contributions can be handled without the need to add vectors. Analyze Let's assume the rod is lying along the x-axis, dx is the length of one small segment, and dg is the charge on --Select--- v Because the rod has a charge per unit length a, the charge dg on the small segment is dg = a dx. Find the magnitude of the electric field at P due to one segment of the rod having a charge dg. (Use the following as necessary: a, k, 1, e, and x.) dx da dE = k = x² Find the total field at P using the equation for the electric field due to a continuous charge distribution: --?-- v E = Noting that k. and 1 = 2 are constants and can be removed from the integral, evaluate the integral. (Use the following as necessary: a, k, e, and Q.) -7- v -2-- v E - kA 1 (1) E = Finalize We see that our prediction is correct; if a becomes larger, the denominator of the fraction grows larger, and E--Select- . On the other hand, if a → 0, which corresponds to sliding the bar to the left until its left end is at the origin, then E - o. That represents the condition in which the observation point Pis at zero distance from the charge at the end of the rod, so the field becomes infinite. EXERCISE A rod 17.0 cm long is uniformly charged and has a total charge of –25.0 µC. Hint (a) Determine the magnitude of the electric field (in N/C) along the long axis of the rod at a point 37.0 cm from its center.
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