Electromagnetism Physics Problems: Get Expert Help with Plainmath

Fire doors are doors that can slow the spread of fire from room to room when they are closed. In some buildings, fire doors are held open by electromagnets. bxplain why electromagnets are Used instead of permanent magnets.

How can we draw magnetic field lines?

Hypothetically, why can't we wrap copper wires around car axles and turn them into electromagnets to help charge the batteries?

If you hold a bar magnet in each hand and bring your hands close together, will the force be attractive or repulsive if the magnets are held in the following ways? a. the two north poles are brought close together. b. a north pole and a south pole are brought together.

A bar magnet whose magnetic dipole moment is $15A\ast <!--\; \ast \; -->m^2$ is aligned with an applied magnetic field of 4 T. How much work must you do to rotate the bar magnet ${180}^{\circ <!--\; \circ \; -->}$ to point in the direction opposite to the magnetic field?

An iron bar magnet having a coercivity of 7000 A/m is to be demagnetized. If the bar is inserted within a cylindrical wire coil 0.25 m long and having 150 turns, what electric current is required to generate the necessary magnetic field?

A working electric motor needs to have three things. Which of the following are the three?
a. a device to switch the electromagnets at the right time
b. a moving element with magnets
c. an even number of magnets
d. a stationary element with magnets

The earth may have even reversed the direction of its field several times during its history of 4 to 5 billion years. How can geologists know about the earth’s field in past?

Can the magnetic force between two magnets be explained classically via magnetization current?
Usually in Electrodynamics courses the magnetic forces are analysed via wire-wire interaction. I don't remember being shown a classical explanation for magnetic forces between magnets. Since it is a quantum system caused mainly by the alignment of spins/magnetic moments, I was wondering if the magnetic force between two magnetized ferromagnets can be explained via Lorentz force on the small magnetization currents formed within the material (even if they are just a mathematical tool in this case).

Both English physicist Michael Faraday and American physicist Joseph Henry independently discovered electromagnetic induction at about the same time. In Henry's electrical experiments, his wife donated part of her wedding gown for silk to cover the wires of Henry's electromagnets. What was the purpose of the silk covering?

How is a magnetic field generated?

We are looking to create a fairly small 10-20lb electromagnet. What we need this to be able to do is create down force from a range of say 3-4 feet.
So when holding the magnet at around 3 feet it could create 20+ pounds of pull towards the metal sheet below(for a total pull of 40+lbs assuming the magnet itself is 20lbs). Just curious if this would be possible in the scale that is needed. We could pretty easily do the reverse and have the electromagnet at the bottom and the metal being pulled to the magnet but this is just not as practical for our project.

Magnetic Force on a current carrying conductor
Why does a current carrying conductor parallel to the magnetic field not experience a force?

Why does the magnitude of magnetic force which one moving charge exerts on another charge appears inconsistent in different frames of reference?
I have a fundamental misunderstanding about the definition of magnetic force as arises from Lorenz force: $F=q\stackrel{\to <!--\; \to \; -->}{v}\times <!--\; \times \; -->\stackrel{\to <!--\; \to \; -->}{B}$. According to a basic fact of electromagnetism, electric currents are the source of magnetic fields, and a single moving charge can be viewed as a current. Therefore, in a situation of one moving charge and another stationary charge, the moving charge creates a magnetic field, but by the Lorenz definition of magnetic force, the force experienced by the stationary charge iz zero (since it's velocity is zero). But if we shift to a frame of reference moving at half the speed ($\frac{v}{2}$) of the first charge and in the same direction, we get one charge moving in a speed $+\frac{v}{2}$ and a second charge moving at $-<!--\; -\; -->\frac{v}{2}$. In this scenario, the magnetic force experienced by the same charge is not zero.
So what exactly am i missing? i view it as a serious bug in my fundamental understanding of electromagnetism, and i will be extremely thankful if someone will complete for me the picture of charge-charge electromagnetic interaction.

Why don't we simply define the magnetic field to point on the direction of magnetic force that acts on the moving charge?

Earth has a magnetic dipole moment of $8.0\cdot <!--\; \cdot \; -->{10}^{22}J/T$.(a) What current would have to be produced in a single turn of wire extending around Earth at its geomagnetic equator if we wished to set up such a dipole? Could such an arrangement be used to cancel out Earth’s magnetism (b) at points in space wellabove Earth’s surface or (c) on Earth’s surface?

One of the ways nuclear fusion happens in the sun is deuterium and tritium fusion which forms a Helium-4 atom and a neutrino. What flavor of neutrino is created - a tau, muon, or electron neutrino?

True or false: Ampere's law (with displacement current) is one of Maxwell's Equations:
a. True
b. False, even the names are different

Magnetic force between two long conductive wires with current
I was asked to calculate the total magnetic force between two long conductive wires with current on them, flowing in the same direction. I used the formula $F_1={\mu }_o\frac{I_1{I}_{2}l}{2\pi d}$ and got a numerical answer. I then doubled that answer to account for both forces (from either wire to the other). The answer key gives the same number I found, but without doubling it. I do not understand why, because it clearly states in the book that said formula is for the force experienced by wire 1, caused by wire 2, which disregards the force experienced by wire 2, caused by wire 1.

A bar magnet with magnetic dipole moment $0.54A{m}^2$ lies on the negative x axis. A compass is located at the origin. Magnetic north is in the negative z direction. Between the bar magnet and the compass is a coil of wire of radius 3.5 cm, connected to batteries not shown. The distance from the center of the coil to the center of the compass is 9.7 cm. The distance from the center of the bar magnet to the center of the compass is 22.5 cm. A steady current of 0.96 A runs through the coil. Conventional current runs clockwise in the coil when viewed from the location of the compass. Despite the presence of the coil and the bar magnet, the compass points north. (a) Which end of the bar magnet is closer to the compass