How are solenoids and electromagnets used in galvanometers, electric motors, and loudspeakers?

Braylon Lester
2022-07-23
Answered

How are solenoids and electromagnets used in galvanometers, electric motors, and loudspeakers?

You can still ask an expert for help

Reinfarktq6

Answered 2022-07-24
Author has **18** answers

These devices change electrical energy into the mechanical energy

They change electrical energy into mechanical.

They change electrical energy into mechanical.

asked 2022-05-19

I know that there is some relationship between electric current and magnetism, but I am having trouble pinning down the exact relationship. Is electric current a necessary condition for the existence of magnetic field? And is electric current a sufficient condition for the existence of magnetic field?

In other words, is it true that "there is electric current if and only if there is a magnetic field"?

In other words, is it true that "there is electric current if and only if there is a magnetic field"?

asked 2022-07-21

If an aluminum sheet is held between the poles of a large bar magnet, it requires some force to pull it out of the magnetic field even though the sheet is not ferromagnetic and does not touch the pole faces.

Explain.

Explain.

asked 2022-07-23

What is the correct frame of reference for determining the magnetic force on a charge?

If two charges are both stationary in a given inertial frame, F1, then neither charge should experience a magnetic force due to the presence of the other charge (qv = 0). If we accelerate one charge, but not the other, then again, neither charge should experience a magnetic force, since only one charge has a non-zero velocity as measured in that inertial frame, meaning the other, stationary charge will experience no force in the magnetic field of the moving charge.

Now imagine that we are riding along as part of another inertial frame, F2, and that the first inertial frame discussed above that contains the two electrons F1, is traveling at a relative velocity of v from our perspective (i.e., it’s moving faster than us). Now imagine that we fire two electrons from our inertial frame F2, towards F1, one that travels at a velocity of v from our perspective, thereby traveling at the same velocity as the electron that appeared stationary in F1, and another that travels at the same velocity as the second, "faster" electron.

From our perspective in F2, both electrons have a non-zero velocity: the “slow one” traveling at a velocity of v, and the “fast one” traveling a bit faster than that. From our perspective, in F2, both electrons should experience a magnetic force of attraction due to their non-zero velocities in non-zero magnetic fields, which would change the path of those electrons from the perspective of both inertial frames.

However, from the perspective of F1, the “slow” electron is stationary, and should not experience any magnetic force in any magnetic field.

This seems to not make sense - what would happen as an experimental matter?

If two charges are both stationary in a given inertial frame, F1, then neither charge should experience a magnetic force due to the presence of the other charge (qv = 0). If we accelerate one charge, but not the other, then again, neither charge should experience a magnetic force, since only one charge has a non-zero velocity as measured in that inertial frame, meaning the other, stationary charge will experience no force in the magnetic field of the moving charge.

Now imagine that we are riding along as part of another inertial frame, F2, and that the first inertial frame discussed above that contains the two electrons F1, is traveling at a relative velocity of v from our perspective (i.e., it’s moving faster than us). Now imagine that we fire two electrons from our inertial frame F2, towards F1, one that travels at a velocity of v from our perspective, thereby traveling at the same velocity as the electron that appeared stationary in F1, and another that travels at the same velocity as the second, "faster" electron.

From our perspective in F2, both electrons have a non-zero velocity: the “slow one” traveling at a velocity of v, and the “fast one” traveling a bit faster than that. From our perspective, in F2, both electrons should experience a magnetic force of attraction due to their non-zero velocities in non-zero magnetic fields, which would change the path of those electrons from the perspective of both inertial frames.

However, from the perspective of F1, the “slow” electron is stationary, and should not experience any magnetic force in any magnetic field.

This seems to not make sense - what would happen as an experimental matter?

asked 2022-05-17

A metal conductor of length 1 m rotates vertically about one of its ends at angular velocity 5 rad/s . If the horizontal component of earth’s magnetism is $2\times {10}^{-5}T$, then voltage developed between the two ends of the conductor is ?

asked 2022-04-12

Consider the circuit shown in

photo

A)What are the magnitude and direction of the current in the $20\mathrm{\Omega}$

resistor in figure

Express your answer with the appropriate units. Enter positive value if the current is clockwise and negative value if the current is counterclockwise.

photo

A)What are the magnitude and direction of the current in the $20\mathrm{\Omega}$

resistor in figure

Express your answer with the appropriate units. Enter positive value if the current is clockwise and negative value if the current is counterclockwise.

asked 2022-05-10

Magnetic force between moving charges

Given two infinite parallel charged rods with equal charge density $\lambda $. They are moving with same constant velocity $\overrightarrow{v}$ parallel to the rods. Find the speed $v$ for which the magnetic attraction is equal to the electrostatic repulsion.

Well, I know how to solve this problem: we first find out the magnetic field created by one rod on the other using Biot's and Savart's law, then we use the definition of $\overrightarrow{B}$ ( $d\overrightarrow{F}=\overrightarrow{v}dq\times \overrightarrow{B}$ ) to find the magnetic force, then equate magnetic and electrostatic forces to find $v$, which will be greater than or equal to $c$, thus conclude it is impossible for the forces to be equal.

However, one can argue as the following:

We all know that "same laws of physics apply in all inertial frames". With a constant velocity $\overrightarrow{v}$,the rest frame of the rods is an inertial frame. Therefore, if Biot-Savart law applies in our frame, it has to apply in the rest frame. If so, none of the rods will feel a magnetic field from the other one because their relative speed is zero, and there will be no magnetic force between the rods.

I've seen this question several times before in references, exams, exercise sheets,and in many different forms (parallel planes, beam of electrons ...),but no one ever used this argument.What is the problem in it ? Is it something related to Maxwell's equations or special relativity ? Or what else ?

I know a similar question was asked before, but the answers weren't satisfying. Please provide your answers with necessary mathematics.

Given two infinite parallel charged rods with equal charge density $\lambda $. They are moving with same constant velocity $\overrightarrow{v}$ parallel to the rods. Find the speed $v$ for which the magnetic attraction is equal to the electrostatic repulsion.

Well, I know how to solve this problem: we first find out the magnetic field created by one rod on the other using Biot's and Savart's law, then we use the definition of $\overrightarrow{B}$ ( $d\overrightarrow{F}=\overrightarrow{v}dq\times \overrightarrow{B}$ ) to find the magnetic force, then equate magnetic and electrostatic forces to find $v$, which will be greater than or equal to $c$, thus conclude it is impossible for the forces to be equal.

However, one can argue as the following:

We all know that "same laws of physics apply in all inertial frames". With a constant velocity $\overrightarrow{v}$,the rest frame of the rods is an inertial frame. Therefore, if Biot-Savart law applies in our frame, it has to apply in the rest frame. If so, none of the rods will feel a magnetic field from the other one because their relative speed is zero, and there will be no magnetic force between the rods.

I've seen this question several times before in references, exams, exercise sheets,and in many different forms (parallel planes, beam of electrons ...),but no one ever used this argument.What is the problem in it ? Is it something related to Maxwell's equations or special relativity ? Or what else ?

I know a similar question was asked before, but the answers weren't satisfying. Please provide your answers with necessary mathematics.

asked 2022-05-18

The inverse square law for an electric field is:

$E=\frac{Q}{4\pi {\epsilon}_{0}{r}^{2}}$

Here:

$\frac{Q}{{\epsilon}_{0}}$

is the source strength of the charge. It is the point charge divided by the vacuum permittivity or electric constant, I would like very much to know what is meant by source strength as I can't find it anywhere on the internet. Coming to the point an electric field is also described as:

$Ed=\frac{Fd}{Q}=\mathrm{\Delta}V$

This would mean that an electric field can act only over a certain distance. But according to the Inverse Square Law, the denominator is the surface area of a sphere and we can extend this radius to infinity and still have a value for the electric field. Does this mean that any electric field extends to infinity but its intensity diminishes with increasing length? If that is so, then an electric field is capable of applying infinite energy on any charged particle since from the above mentioned equation, if the distance over which the electric field acts is infinite, then the work done on any charged particle by the field is infinite, therefore the energy supplied by an electric field is infinite. This clashes directly with energy-mass conservation laws. Maybe I don't understand this concept properly, I was hoping someone would help me understand this better.

$E=\frac{Q}{4\pi {\epsilon}_{0}{r}^{2}}$

Here:

$\frac{Q}{{\epsilon}_{0}}$

is the source strength of the charge. It is the point charge divided by the vacuum permittivity or electric constant, I would like very much to know what is meant by source strength as I can't find it anywhere on the internet. Coming to the point an electric field is also described as:

$Ed=\frac{Fd}{Q}=\mathrm{\Delta}V$

This would mean that an electric field can act only over a certain distance. But according to the Inverse Square Law, the denominator is the surface area of a sphere and we can extend this radius to infinity and still have a value for the electric field. Does this mean that any electric field extends to infinity but its intensity diminishes with increasing length? If that is so, then an electric field is capable of applying infinite energy on any charged particle since from the above mentioned equation, if the distance over which the electric field acts is infinite, then the work done on any charged particle by the field is infinite, therefore the energy supplied by an electric field is infinite. This clashes directly with energy-mass conservation laws. Maybe I don't understand this concept properly, I was hoping someone would help me understand this better.