/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 42 A \(15.0-\mathrm{cm}\) -long sol... [FREE SOLUTION] | 91Ó°ÊÓ

91Ó°ÊÓ

A \(15.0-\mathrm{cm}\) -long solenoid with radius \(0.750 \mathrm{~cm}\) is closely wound with 600 turns of wire. The current in the windings is 8.00 A. Compute the magnetic field at a point near the center of the solenoid.

Short Answer

Expert verified
The magnetic field at the center of the solenoid is approximately \(0.02 T\).

Step by step solution

01

Understand and note down given parameters

List out the values given in the problem. We have - Length of solenoid (\(l\)) = 15.0 cm = 0.15 m (always ensure to keep units in SI), Current (\(I\)) = 8.00 A, Number of turns (\(n\)) = 600, and radius (\(r\)) = 0.750 cm = 0.0075 m (not needed for the calculation).
02

Calculate the number of turns per unit length

In the formula for magnetic field, we need the number of turns per unit length (\(n'\)), not just the total number of turns. \(n'\) is calculated by dividing the total number of turns (\(n\)) by the length (\(l\)) of the solenoid. The formula is \(n' = n / l\). Substitute the values we have for \(n\) and \(l\) to find \(n'\).
03

Apply the formula for the magnetic field

The formula for the magnetic field (\(B\)) inside a solenoid is given by \(B = \mu_0 * n' * I\). Here, \(\mu_0\) is the permeability of free space, which equals \(4\pi * 10^{-7} T*m/A\). Now substitute the values of \(\mu_0\), \(n'\), and \(I\) into the formula to calculate \(B\).

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Key Concepts

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

Solenoid
Imagine a solenoid as a long coil of wire tightly wound into a cylindrical shape. When an electric current flows through it, the solenoid creates a magnetic field similar to that of a bar magnet. Solenoids are integral components in various devices, ranging from electromagnets to inductors and transformers.
One of the fascinating features of a solenoid is its ability to produce a uniform magnetic field inside its core. This uniform field depends on certain factors, such as the number of turns in the coil and the current passing through the wire. The field is strongest at the center and diminishes towards the ends of the solenoid. This makes solenoids extremely useful in creating controlled magnetic environments.
  • Long, tightly wound coil
  • Generates a uniform magnetic field
  • Field strength depends on current and coil turn density
Current
Current is the flow of electric charge, usually carried by moving electrons in a conductor. In the case of a solenoid, current is crucial because it directly influences the strength of the magnetic field produced. When you increase the current flowing through the solenoid's coil, the magnetic field also intensifies and vice versa.
In our problem, the current through the solenoid's windings is given as 8.00 A. This means a steady flow of charge is generating a magnetic field within the coil. To maximize the effect of this current and create a strong field, the solenoid should have tightly packed turns, which we've calculated. Always remember that in most applications, ensuring a consistent current is key to maintaining a stable magnetic field.
  • Flow of electric charge
  • Measured in amperes (A)
  • Directly affects magnetic field strength
Magnetic Field Calculation
Magnetic field calculation in a solenoid involves understanding how the magnetic field (B) is affected by various parameters. The formula for finding the magnetic field at the center of a solenoid is:\[B = \mu_0 * n' * I\]
Here, \(B\) represents the magnetic field strength, \(\mu_0\) is the permeability of free space given as \(4\pi * 10^{-7} \ T*m/A\), \(n'\) is the number of turns per unit length, and \(I\) is the current in amperes.
Using this formula, you can calculate the field within the solenoid. Remember, this formula provides an accurate result considering an ideal situation, where the solenoid is infinitely long or the point is close to the center. Such conditions ensure the magnetic field is most uniform.
  • Key formula: \(B = \mu_0 * n' * I\)
  • Strongest near the center of solenoid
  • Depends on current and number of turns per unit length
Number of Turns Per Unit Length
The number of turns per unit length in a solenoid, often denoted as \(n'\), is a critical factor in determining the magnetic field strength. To find \(n'\), divide the total number of turns by the solenoid’s length. This is expressed as:\[n' = \frac{n}{l}\]
In our example, with 600 turns of wire and a solenoid length of 15.0 cm (converted to 0.15 m), we find \(n'\) by dividing 600 by 0.15 m, which results in a significant value showing how densely the wire is packed.
A higher number of turns per unit length typically results in a stronger magnetic field. This is because more wire loops allow more magnetic field lines to be generated within the solenoid, amplifying the magnetic effect.
  • Formula: \(n' = \frac{n}{l}\)
  • Higher \(n'\) correlates with a stronger magnetic field
  • Depends on total turns and solenoid length

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Most popular questions from this chapter

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?

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.

A toroidal solenoid with 400 turns of wire and a mean radius of \(6.0 \mathrm{~cm}\) carries a current of 0.25 A. The relative permeability of the core is \(80 .\) (a) What is the magnetic field in the core? (b) What part of the magnetic field is due to the magnetic moments of the atoms in the core?

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.

A long, straight solid cylinder, oriented with its axis in the \(z\) -direction, carries a current whose current density is \(\overrightarrow{\boldsymbol{J}} .\) The current density, although symmetric about the cylinder axis, is not constant and varies according to the relationship $$ \begin{aligned} \overrightarrow{\boldsymbol{J}} &=\left(\frac{b}{r}\right) e^{(r-a) / \delta} \hat{\boldsymbol{k}} & \text { for } r \leq a \\ &=\mathbf{0} & \text { for } r \geq a \end{aligned} $$ where the radius of the cylinder is \(a=5.00 \mathrm{~cm}, r\) is the radial distance from the cylinder axis, \(b\) is a constant equal to \(600 \mathrm{~A} / \mathrm{m},\) and \(\delta\) is a constant equal to \(2.50 \mathrm{~cm} .\) (a) Let \(I_{0}\) be the total current passing through the entire cross section of the wire. Obtain an expression for \(I_{0}\) in terms of \(b, \delta,\) and \(a .\) Evaluate your expression to obtain a numerical value for \(I_{0}\) (b) Using Ampere's law, derive an expression for the magnetic field \(\overrightarrow{\boldsymbol{B}}\) in the region \(r \geq a\). Express your answer in terms of \(I_{0}\) rather than \(b\). (c) Obtain an expression for the current \(I\) contained in a circular cross section of radius \(r \leq a\) and centered at the cylinder axis. Express your answer in terms of \(I_{0}\) rather than \(b\). (d) Using Ampere's law, derive an expression for the magnetic field \(\overrightarrow{\boldsymbol{B}}\) in the region \(r \leq \underline{a}\). (e) Evaluate the magnitude of the magnetic field at \(r=\delta, r=a,\) and \(r=2 a\)

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