2. Calculate the expected ratio of the magnetic field between the ends of the solenoid (x = L/2 or – L/2) and its center (x = 0) for a finite length solenoid for L~R and L » R cases by using Equation 5.4.

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Chapter16: Electromagnetic Waves
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Consider the rectangular (an amperian loop) path of length L and width w shown in Figure 5.2 (right).
We can apply Ampère's law to this path by evaluating the integral of E-de over each side of the rectangle.
The contribution along side 3 is zero because the magnetic field is zero outside the solenoid. The
contributions from sides 2 and 4 are both zero, because is perpendicular to då along these paths, both
inside and outside the solenoid Side 1 gives a contribution to the integral because along this path 5 is
uniform and parallel to dž, that is, the only contribution comes from path 1.
Blds
Bids
Blds
B=0
fE dš = B đš + B-dš + B đš + B-d3 = BL = 4olenci
path 1
path 2
path 3
path 4
If N is the mumber of tums in the length L, the total curent through the rectangle is NI. Therefore,
Ampère's law applied to this path gives
N
B-ds = BL = H9NI =B = H0 = Honl
5.2
where n = N/L is the number of tums per unit length.
Consider a section of the solenoid of length dx'. The total current winding around the solenoid in that
section is dI = nidx'. This section is located at a distance x – x' away from the point P. The contribution
to the magnetic field at P due to this subset of loops is
HOR?
2[(x – x')² + R²]ª/2
HOR?
dB =
dl =-
5.3
2[(x - x')? + R2j3/2 nldx
Integrating over the entire length of the solenoid, we obtain
+L/2
|+L/2
dx'
HonIR?
(x – x')
[(x – x')² + R°j³/2
R²[(x – x')² + R*Il_1/2
Honi
x+L/2
x- L/2
5.4
2 l
(x +L/2)2 +R2
V(x- L/2)² + R²
Equation 5.4 expresses the change of magnetic field depending on the distance from the center.
Transcribed Image Text:Consider the rectangular (an amperian loop) path of length L and width w shown in Figure 5.2 (right). We can apply Ampère's law to this path by evaluating the integral of E-de over each side of the rectangle. The contribution along side 3 is zero because the magnetic field is zero outside the solenoid. The contributions from sides 2 and 4 are both zero, because is perpendicular to då along these paths, both inside and outside the solenoid Side 1 gives a contribution to the integral because along this path 5 is uniform and parallel to dž, that is, the only contribution comes from path 1. Blds Bids Blds B=0 fE dš = B đš + B-dš + B đš + B-d3 = BL = 4olenci path 1 path 2 path 3 path 4 If N is the mumber of tums in the length L, the total curent through the rectangle is NI. Therefore, Ampère's law applied to this path gives N B-ds = BL = H9NI =B = H0 = Honl 5.2 where n = N/L is the number of tums per unit length. Consider a section of the solenoid of length dx'. The total current winding around the solenoid in that section is dI = nidx'. This section is located at a distance x – x' away from the point P. The contribution to the magnetic field at P due to this subset of loops is HOR? 2[(x – x')² + R²]ª/2 HOR? dB = dl =- 5.3 2[(x - x')? + R2j3/2 nldx Integrating over the entire length of the solenoid, we obtain +L/2 |+L/2 dx' HonIR? (x – x') [(x – x')² + R°j³/2 R²[(x – x')² + R*Il_1/2 Honi x+L/2 x- L/2 5.4 2 l (x +L/2)2 +R2 V(x- L/2)² + R² Equation 5.4 expresses the change of magnetic field depending on the distance from the center.
2. Calculate the expected ratio of the magnetic field between the ends of the solenoid
(x = L/2 or – L/2) and its center (x = 0) for a finite length solenoid for L~R and L » R cases by
using Equation 5.4.
Transcribed Image Text:2. Calculate the expected ratio of the magnetic field between the ends of the solenoid (x = L/2 or – L/2) and its center (x = 0) for a finite length solenoid for L~R and L » R cases by using Equation 5.4.
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