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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 magnetic field of \(37.2 \mathrm{~T}\) has been achieved at the MIT Francis Bitter Magnet Laboratory. Find the current needed to achieve such a field (a) \(2.00 \mathrm{~cm}\) from a long, straight wire; (b) at the center of a circular coil of radius \(42.0 \mathrm{~cm}\) that has 100 turns; (c) near the center of a solenoid with radius \(2.40 \mathrm{~cm},\) length \(32.0 \mathrm{~cm},\) and 40,000 turns.

A very long, straight horizontal wire carries a current such that \(8.20 \times 10^{18}\) electrons per second pass any given point going from west to east. What are the magnitude and direction of the magnetic field this wire produces at a point \(4.00 \mathrm{~cm}\) directly above it?

To use a larger sample, the experimenters construct a solenoid that has the same length, type of wire, and loop spacing but twice the diameter of the original. How does the maximum possible magnetic torque on a bacterium in this new solenoid compare with the torque the bacterium would have experienced in the original solenoid? Assume that the currents in the solenoids are the same. The maximum torque in the new solenoid is (a) twice that in the original one; (b) half that in the original one; (c) the same as that in the original one; (d) one-quarter that in the original one.

We can estimate the strength of the magnetic field of a refrigerator magnet in the following way: Imagine the magnet as a collection of current-loop magnetic dipoles. (a) Derive the force between two current loops with radius \(R\) and current \(I\) separated by distance \(d \ll R\). Very close to the wire its magnetic field is about the same as for an infinitely long wire, and Eq.( 28.11 ) can be used. (b) Using Eq. ( 28.17 ), express the current \(I\) in terms of the magnetic field at the middle of the loop, and express the radius \(R\) in terms of the area of the loop. In this way, derive an expression for the force \(F\) between two identical current loops separated by a small distance \(d\) in terms of their mutual area \(A\) and center magnetic field \(B\). (c) Rearrange your result to obtain an expression for the magnetic field of a dipole with area \(A\) in terms of the force \(F\) from an identical dipole separated by a small distance \(d\). (d) Now notice that the force it takes to separate one magnet from your refrigerator is nearly the same as the force it takes to separate two magnets stuck together. Estimate that force \(F\). (e) Estimate the area of a refrigerator magnet. (f) Assume that when these magnets are stuck together or to the refrigerator, they are separated by an effective distance \(d=25 \mu \mathrm{m}\). Use the formula derived above to estimate the magnetic field strength of the magnet.

Currents in dc transmission lines can be 100 A or higher. Some people are concerned that the electromagnetic fields from such lines near their homes could pose health dangers. For a line that has current \(150 \mathrm{~A}\) and a height of \(8.0 \mathrm{~m}\) above the ground, what magnetic field does the line produce at ground level? Express your answer in teslas and as a percentage of the earth's magnetic field, which is \(0.50 \mathrm{G}\). Is this value cause for worry?

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