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A long solenoid with 60 turns of wire per centimeter carries a current of 0.15 A. The wire that makes up the solenoid is wrapped around a solid core of silicon steel \(\left(K_{\mathrm{m}}=5200\right) .\) (The wire of the solenoid is jacketed with an insulator so that none of the current flows into the core.) (a) For a point inside the core, find the magnitudes of (i) the magnetic field \(\overrightarrow{\boldsymbol{B}}_{0}\) due to the solenoid current; (ii) the magnetization \(\overrightarrow{\boldsymbol{M}}\) (iii) the total magnetic field \(\overrightarrow{\boldsymbol{B}}\). (b) In a sketch of the solenoid and core, show the directions of the vectors \(\overrightarrow{\boldsymbol{B}}, \overrightarrow{\boldsymbol{B}}_{0},\) and \(\overrightarrow{\boldsymbol{M}}\) inside the core.

Short Answer

Expert verified
The magnitudes of the magnetic field due to solenoid current \(\overrightarrow{\boldsymbol{B}}_{0}\), the magnetization \(\overrightarrow{\boldsymbol{M}}\), the total magnetic field \(\overrightarrow{\boldsymbol{B}}\) are approximately 0.0113 T, 8986 T/m, and 1.1313 T respectively, and their directions are all longitudinally along the length of the solenoid from the end where current enters, to the other end.

Step by step solution

01

Calculate Magnetic Field due to Solenoid

The formula to calculate the magnetic field inside a solenoid is \(\overrightarrow{\boldsymbol{B}}_{0}= \mu_{0} \times n \times I\), where \(\mu_{0}\) is the permeability of free space (4\(\pi \times 10^{-7} T m/A\)), \(n\) is the number of turns per meter, and \(I\) is the current. Hence, \(\overrightarrow{\boldsymbol{B}}_{0}= 4\pi \times 10^{-7} T m/A \times 60 \times 10^{2} turns/m \times 0.15 A = 0.0113 T .\)
02

Calculate Magnetization of Silicon Steel

The magnetization \(\overrightarrow{\boldsymbol{M}}\) of the silicon steel is related to the magnetic field due to the solenoid by \(\overrightarrow{\boldsymbol{M}} = (\overrightarrow{\boldsymbol{B}}_{0}/\mu_{0}) - \overrightarrow{\boldsymbol{B}}_{0}\). Hence, substituting from step 1, we find \(\overrightarrow{\boldsymbol{M}} = (0.0113 T/4 \pi \times 10^{-7} T m/A) - 0.0113 T = 8986 T/m\).
03

Calculate Total Magnetic Field

The total magnetic field \(\overrightarrow{\boldsymbol{B}}\) inside the solenoid is the sum of the field due to the solenoid and the magnetization of the core: \( \overrightarrow{\boldsymbol{B}} = \mu_{0} (\overrightarrow{\boldsymbol{B}}_{0} + \overrightarrow{\boldsymbol{M}}) = 4\pi x 10^{-7} T m/A (0.0113 T + 8986 T/m) = 1.1313 T.
04

Determine the direction of vectors

The directions of the vectors \(\overrightarrow{\boldsymbol{B}}, \overrightarrow{\boldsymbol{B}}_{0},\) and \(\overrightarrow{\boldsymbol{M}}\) are all the same, longitudinally along the length of the solenoid from the end where current enters the solenoid to the other end, corresponding to the 'thumb' direction of the right-hand rule when the 'fingers' are curled in the direction of current.

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Key Concepts

These are the key concepts you need to understand to accurately answer the question.

Magnetization
Magnetization is a fascinating concept that refers to how materials respond to magnetic fields. It signifies the degree to which a material becomes magnetized when it is placed within a magnetic field. In our exercise, we're looking at a solenoid's core made of silicon steel. This core becomes magnetized due to the magnetic field generated by the current flowing through the solenoid. The magnetization, denoted by \( \overrightarrow{\boldsymbol{M}} \), is a vector quantity. Its direction is the same as that of the applied magnetic field, and its magnitude depends on the material's properties and the strength of the applied field.

In the problem, we used a particular formula for calculating magnetization:
  • \( \overrightarrow{\boldsymbol{M}} = \left(\overrightarrow{\boldsymbol{B}}_{0}/\mu_{0}\right) - \overrightarrow{\boldsymbol{B}}_{0} \)
By substituting the known values, we determined that the magnetization of the silicon steel core is \( 8986 \ T/m \). This showcases how the core significantly enhances the internal magnetic field due to its high magnetization capacity.
Permeability
Permeability is a vital concept when discussing magnetic materials and fields. It represents how well a material can support the formation of a magnetic field within itself. Every material has a
  • "absolute permeability,"
  • "relative permeability,"
and this describes its response to the magnetic field. The permeability of free space, \( \mu_{0} \), is a constant and is equal to \( 4\pi \times 10^{-7} \ T m/A \).

When considering the solenoid and its core in our problem, we need to also think about the "relative permeability" of the core material. In this exercise, we're dealing with silicon steel, which has a high relative permeability \( K_{\mathrm{m}} \) given as 5200. This high value indicates that the silicon steel core significantly amplifies the magnetic field produced by the solenoid. The relationship between relative permeability and magnetization can be seen in how we calculate the magnetic field and factor in magnetization effects. Knowing a material's permeability is essential when designing systems that use magnetic fields, like transformers, inductors, and our solenoid.
Magnetic Field Calculation
Calculating the magnetic field within a solenoid is a key step for many physics problems. Solenoids are essentially coils of wire that generate magnetic fields when an electric current passes through them. In our given exercise, we calculate the magnetic field inside a solenoid using the formula:
  • \( \overrightarrow{\boldsymbol{B}}_{0}= \mu_{0} \times n \times I \)
where \( \mu_{0} \) is the permeability of free space, \( n \) is the number of turns per meter, and \( I \) is the current.

For the exercise, the solenoid has 60 turns per centimeter, which translates to 6000 turns per meter. With a current of 0.15 A, the magnetic field produced by the solenoid alone, \( \overrightarrow{\boldsymbol{B}}_{0} \), was calculated as approximately 0.0113 T.

In addition to this, when you have a core material like silicon steel within the solenoid, you must also calculate the total magnetic field which includes the effects of magnetization. The formula for the total magnetic field \( \overrightarrow{\boldsymbol{B}} \) becomes:
  • \( \overrightarrow{\boldsymbol{B}} = \mu_{0} (\overrightarrow{\boldsymbol{B}}_{0} + \overrightarrow{\boldsymbol{M}}) \)
Using this, we calculated the total magnetic field as \( 1.1313 \ T \), showing how much stronger the field becomes with a magnetized core.

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Most popular questions from this chapter

A short current element \(d \vec{l}=(0.500 \mathrm{~mm}) \hat{\jmath}\) carries a current of 5.40 A in the same direction as \(d \vec{l}\). Point \(P\) is located at \(\vec{r}=(-0.730 \mathrm{~m}) \hat{\imath}+(0.390 \mathrm{~m}) \hat{\boldsymbol{k}}\). Use unit vectors to express the mag- netic field at \(P\) produced by this current element.

At a particular instant, charge \(q_{1}=+4.80 \times 10^{-6} \mathrm{C}\) is at the point \((0,0.250 \mathrm{~m}, 0)\) and has velocity \(\overrightarrow{\boldsymbol{v}}_{1}=\left(9.20 \times 10^{5} \mathrm{~m} / \mathrm{s}\right) \hat{\boldsymbol{\imath}} .\) Charge \(q_{2}=-2.90 \times 10^{-6} \mathrm{C}\) is at the point \((0.150 \mathrm{~m}, 0,0)\) and has velocity \(\overrightarrow{\boldsymbol{v}}_{2}=\left(-5.30 \times 10^{5} \mathrm{~m} / \mathrm{s}\right) \hat{\jmath} .\) At this instant, what are the magnitude and\ direction of the magnetic force that \(q_{1}\) exerts on \(q_{2} ?\)

A plasma is a gas of ionized (charged) particles. When plasma is in motion, magnetic effects "squeeze" its volume, inducing inward pressure known as a pinch. Consider a cylindrical tube of plasma with radius \(R\) and length \(L\) moving with velocity \(\overrightarrow{\boldsymbol{v}}\) along its axis. If there are \(n\) ions per unit volume and each ion has charge \(q\), we can determine the pressure felt by the walls of the cylinder. (a) What is the volume charge density \(\rho\) in terms of \(n\) and \(q ?\) (b) The thickness of the cylinder "surface" is \(n^{-1 / 3}\). What is the surface charge density \(\sigma\) in terms of \(n\) and \(q ?\) (c) The current density inside the cylinder is \(\vec{J}=\rho \overrightarrow{\boldsymbol{v}}\). Use this result along with Ampere's law to determine the magnetic field on the surface of the cylinder. Denote the circumferential unit vector as \(\hat{\phi}\). (d) The width of a differential strip of surface current is \(R d \phi .\) What is the differential current \(d I_{\text {surface }}\) that flows along this strip? (e) What differential force is felt by this strip due to the magnetic field generated by the volume current? (f) Integrate to determine the total force on the walls of the cylinder; then divide by the wall area to obtain the pressure in terms of \(n, q, R\), and \(v\). (g) If a plasma cylinder with radius \(2.0 \mathrm{~cm}\) has a charge density of \(8.0 \times 10^{16}\) ions \(/ \mathrm{cm}^{3},\) where each ion has a charge of \(e=1.6 \times 10^{-19} \mathrm{C}\) and is moving axially with a speed of \(20.0 \mathrm{~m} / \mathrm{s},\) what is its pinch pressure?

The magnetic field around the head has been measured to be approximately \(3.0 \times 10^{-8} \mathrm{G}\). Although the currents that cause this field are quite complicated, we can get a rough estimate of their size by modeling them as a single circular current loop \(16 \mathrm{~cm}\) (the width of a typical head) in diameter. What is the current needed to produce such a field at the center of the loop?

A long, straight wire lies along the \(x\) -axis and carries current \(I_{1}=2.00 \mathrm{~A}\) in the \(+x\) -direction. A second wire lies in the \(x y\) -plane and is parallel to the \(x\) -axis at \(y=+0.800 \mathrm{~m}\). It carries current \(I_{2}=6.00 \mathrm{~A}\), also in the \(+x\) -direction. In addition to \(y \rightarrow \pm \infty,\) at what point on the \(y\) -axis is the resultant magnetic field of the two wires equal to zero?

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