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A wire \(50.0 \mathrm{~cm}\) long carries a \(0.500 \mathrm{~A}\) current in the positive direction of an \(x\) axis through a magnetic field \(\vec{B}=\) \((3.00 \mathrm{mT}) \hat{\mathrm{j}}+(10.0 \mathrm{mT}) \mathrm{k}\). In unit-vector notation, what is the magnetic force on the wire?

Short Answer

Expert verified
The magnetic force is \( -2.5 \times 10^{-3} \hat{j} + 0.750 \times 10^{-3} \hat{k} \) N.

Step by step solution

01

Identify Known Values

Let's first identify the given values in the problem. The length of the wire, \( L \), is 50.0 cm, which we convert to meters: \( 0.500 \) m. The current, \( I \), is 0.500 A. The magnetic field, \( \vec{B} \), is \( (3.00 \text{ mT}) \hat{\mathrm{j}} + (10.0 \text{ mT}) \mathrm{k} \). We convert this to teslas: \( \vec{B} = (3.00 \times 10^{-3} \text{ T}) \hat{\mathrm{j}} + (10.0 \times 10^{-3} \text{ T}) \mathrm{k} \). The current is in the positive \( x \)-axis direction, \( \hat{i} \).
02

Apply the Lorentz Force Formula

The formula for the magnetic force on a current-carrying wire is \( \vec{F} = I (\vec{L} \times \vec{B}) \), where \( \vec{L} = L \hat{i} \). Substitute \( L = 0.500 \), \( \hat{i} \), and \( \vec{B} = (3.00 \times 10^{-3} \hat{j} + 10.0 \times 10^{-3} \hat{k}) \).
03

Calculate the Cross Product

Compute the cross product \( \vec{L} \times \vec{B} \). Since \( \vec{L} = 0.500 \hat{i} \), we use the distributive properties and cross product rules: \( \hat{i} \times \hat{j} = \hat{k} \) and \( \hat{i} \times \hat{k} = -\hat{j} \). Therefore, \( \vec{L} \times \vec{B} = 0.500 (3.00 \times 10^{-3}) \hat{k} - 0.500 (10.0 \times 10^{-3}) \hat{j} = 1.5 \times 10^{-3} \hat{k} - 5.0 \times 10^{-3} \hat{j} \).
04

Calculate the Magnetic Force

Now substitute back into the formula to get \( \vec{F} = 0.500 [(1.5 \times 10^{-3}) \hat{k} - (5.0 \times 10^{-3}) \hat{j}] = 0.750 \times 10^{-3} \hat{k} - 2.5 \times 10^{-3} \hat{j} \), simplifying to \( \vec{F} = -2.5 \times 10^{-3} \hat{j} + 0.750 \times 10^{-3} \hat{k} \).
05

Express the Magnetic Force

The force on the wire in unit vector notation is now written as \( \vec{F} = -2.5 \times 10^{-3} \hat{j} + 0.750 \times 10^{-3} \hat{k} \) N.

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Key Concepts

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

Current-Carrying Wire
A current-carrying wire is a fundamental concept in physics and engineering. It's essentially a pathway through which electric currents flow. In our problem, a wire is carrying a current of 0.500 A. This means there's a stream of electrons moving through the wire at this specific rate. The direction of the current is in the positive x-axis, denoted as \( \hat{i} \).

When current flows through a wire placed in a magnetic field, it experiences a force. This is what we aim to calculate in the original problem. The interaction between the flow of the electrons (current) and the magnetic field around them is what causes this force.

Understanding how wires carrying current interact with magnetic fields is crucial in applications like motors and generators. These devices harness the principles of electromagnetism to convert electrical energy into mechanical work, or vice versa.
Lorentz Force
The Lorentz force is a key principle when dealing with electric currents in magnetic fields. Named after the physicist Hendrik Lorentz, it describes how a current-carrying wire experiences a force within a magnetic field. The formula for the magnetic component of the Lorentz force is \( \vec{F} = I (\vec{L} \times \vec{B}) \).

- \( \vec{F} \) is the magnetic force acting on the wire- \( I \) is the current flowing through the wire- \( \vec{L} \) is a vector representing the length and direction of the wire
- \( \vec{B} \) represents the magnetic field

This force is perpendicular to both the current and the magnetic field. It's what makes motors spin and drives electromagnetic rails. To calculate it, you often use the cross product of vectors, which we'll explain further.
Cross Product
The cross product is a mathematical operation used when two vectors are involved, like the current-carrying wire and the magnetic field in our problem. It results in a third vector that's perpendicular to the plane created by the first two vectors.

For the problem, we compute \( \vec{L} \times \vec{B} \) where \( \vec{L} = 0.500 \hat{i} \) and \( \vec{B} = (3.00 \times 10^{-3}) \hat{j} + (10.0 \times 10^{-3}) \hat{k} \).

Following the rules for cross products:
  • \( \hat{i} \times \hat{j} = \hat{k} \)
  • \( \hat{i} \times \hat{k} = -\hat{j} \)
We find \( \vec{L} \times \vec{B} = 1.5 \times 10^{-3} \hat{k} - 5.0 \times 10^{-3} \hat{j} \).

Computing cross products can seem tricky, but practice makes it easier. It's crucial for solving problems involving forces in three dimensions.
Magnetic Field
A magnetic field describes the invisible forces that magnets exert around them. The field in the problem is given by \( \vec{B} = (3.00 \times 10^{-3}) \hat{j} + (10.0 \times 10^{-3}) \hat{k} \), indicating its strength and direction.

- \( \hat{j} \) and \( \hat{k} \) are unit vectors describing the field's direction in terms of the y and z axes, respectively
- The numbers denote the field strength in milliteslas (mT), converted to teslas in calculations

A magnetic field interacts with the electric currents and magnetic materials around it. This interaction is responsible for the force that we calculate in the problem. Understanding the properties and influences of magnetic fields is vital in electrical engineering, particularly for designing circuits and electronic devices.

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Most popular questions from this chapter

A \(5.0 \mu \mathrm{C}\) particle moves through a region containing the uniform magnetic field \(-20 \hat{\mathrm{i}} \mathrm{mT}\) and the uniform electric field \(300 \hat{\mathrm{J}} / \mathrm{m} .\) At a certain instant the velocity of the particle is \((17 \mathrm{i}-11 \hat{\mathrm{j}}+7.0 \hat{\mathrm{k}}) \mathrm{km} / \mathrm{s}\). At that instant and in unit-vector nota- tion, what is the net electromagnetic force (the sum of the electric and magnetic forces) on the particle?

A magnetic dipole with a dipole moment of magnitude \(0.020 \mathrm{~J} / \mathrm{T}\) is released from rest in a uniform magnetic field of magnitude \(52 \mathrm{mT}\). The rotation of the dipole due to the magnetic force on it is unimpeded. When the dipole rotates through the orientation where its dipole moment is aligned with the magnetic field, its kinetic energy is \(0.80 \mathrm{~mJ}\). (a) What is the initial angle between the dipole moment and the magnetic field? (b) What is the angle when the dipole is next (momentarily) at rest?

A long, rigid conductor, lying along an \(x\) axis, carries a current of \(5.0 \mathrm{~A}\) in the negative \(x\) direction. A magnetic field \(\vec{B}\) is present, given by \(\vec{B}=3.0 \hat{i}+8.0 x^{2} \hat{j}\), with \(x\) in meters and \(\vec{B}\) in milliteslas. Find, in unit-vector notation, the force on the \(2.0 \mathrm{~m}\) segment of the conductor that lies between \(x=1.0 \mathrm{~m}\) and \(x=3.0 \mathrm{~m}\).

A source injects an electron of speed \(v=1.5 \times 10^{7} \mathrm{~m} / \mathrm{s}\) into a uniform magnetic field of magnitude \(B=1.0 \times 10^{-3} \mathrm{~T}\). The velocity of the electron makes an angle \(\theta=10^{\circ}\) with the direction of the magnetic field. Find the distance \(d\) from the point of injection at which the electron next crosses the field line that passes through the injection point.

A wire of length \(25.0 \mathrm{~cm}\) carrying a current of \(4.51 \mathrm{~mA}\) is to be formed into a circular coil and placed in a uniform magnetic field \(\vec{B}\) of magnitude \(5.71 \mathrm{mT}\). If the torque on the coil from the field is maximized, what are (a) the angle between \(\vec{B}\) and the coil's magnetic dipole moment and (b) the number of turns in the coil? (c) What is the magnitude of that maximum torque?

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