Why electrons move at a uniform speed inside a magnetic field and accelerate in an electric field

When the electron is moving in the magnetic field, if the initial velocity is parallel to the magnetic field, the motion of the electron is not affected by the magnetic field force (Lorentz force), so the electron is still in a state of uniform linear motion, if the initial velocity is not parallel to the magnetic field, the motion of the electron is subject to the magnetic field force (Lorentz force), but the direction of the Lorentz force is perpendicular to the direction of motion, and the Lorentz force can only change the direction of the velocity and cannot change the magnitude of the velocity, so the velocity of the electron does not change. So electrons move at a uniform speed in the magnetic field.

The electron in the electric field, regardless of the original state, is always subject to the electric field force, if this force is the same as the velocity, then the electron does a uniform acceleration linear motion; If the electric field force is opposite to the initial velocity, the electrons move in a straight line with uniform acceleration; If the electric field force is perpendicular to the initial velocity, the electron moves like a flat throw; If the angle between the electric field force and the initial velocity direction is an acute angle, then the electron moves in a uniform acceleration curve; The angle between the electric field force and the direction of the initial velocity is an obtuse angle, so the electrons move in a uniform deceleration curve. So the motion of electrons in an electric field is not necessarily accelerating.

The electric charge moving in the magnetic field is subject to the Lorentz force, which is perpendicular to the direction of electron motion, and does not do work, so the kinetic energy of the electron does not change, and the velocity does not change. The electric field force is different, it gives the electron an acceleration, and the direction depends on the direction of the electric field, so that the electron continues to accelerate.

The force exerted on the electron in the magnetic field is always perpendicular to the direction of velocity, so the magnetic field does not do work on the electron.

The force of electrons in the electric field always follows the direction of the electric field line, regardless of the direction of velocity, and the electric field will do work on the electrons, and it is not necessarily whether it accelerates or decelerates.

The electrons are only subjected to in the electrostatic fieldElectric field forceaction, not subject to other external forces, then the electrons are subjected to constant force, cautious typeAccelerationConstant, do a constant acceleration of the uniform speed movement.

The charged particles move in the electric field, and the flat throwing motion is the same as the previous flat throwing motion, so that the knowledge points can be consolidated and the new knowledge points can be fully utilized. The conclusion that the charged particles move in the electric field can be better preserved.

Electron. It is the earliest elementary particle discovered.

Negatively charged, the electric amount is coulomb, which is the smallest unit of the base base of the electric power, and the mass is, which is often represented by the symbol E. It was discovered in 1897 by the British physicist Joseph John Thomson while studying cathode rays. All atoms consist of a positively charged nucleus.

and a number of electrons moving around it.

The motion of charged particles in a uniform magnetic field is as follows.

Uniform linear motion.

When v b, the charged particles move in a uniform straight line with velocity v.

Uniform circular motion.

When v b, the charged particles are perpendicular to the magnetic inductance line.

The plane moves in a uniform circular motion with the incident velocity.

Problems with the motion of charged particles.

1. Acceleration problem in electric field.

Charged particles are only subjected to the electric field force in the electric field.

role of the problem. If in a uniform electric field, the problem can be solved according to Newton's laws of motion.

Combined with kinematic formulas or kinetic energy theorems.

Differential line processing. However, the problem in the non-uniform electric field can only be solved according to the kinetic energy theorem.

2. Deflection in the electric field.

The charged particles enter the electric field at a certain speed and at a certain angle to the electric field, so that the direction of force of the charged particles is not in the same straight line as the direction of velocity, and the particles will move in a curve.

It is common for charged particles to be injected into the electric field in the direction of the perpendicular electric field, and the analysis method of this kind of problem is the same as the analysis method of the flat motion problem, which decomposes the motion of the particle into a uniform acceleration motion along the direction of force and a uniform motion in the direction of initial velocity. The main problems to be solved are the terminal velocity, deflection distance, and deflection angle of charged particles.

3. Deflection in magnetic fields.

A charged particle that is injected into a magnetic field, as long as its velocity direction is at an angle to the magnetic field. It is subjected to the Lorentz force of the magnetic field on it.

Function. If a charged particle is injected perpendicularly into a uniform magnetic field, the direction of its initial velocity and the direction of the Lorentz force are in a plane perpendicular to the direction of the magnetic field, and there is no action to cause the particle to leave this plane, so the particle can only move in this plane.

4. Motion problems in composite fields.

The so-called motion in a composite field is the problem of motion in two or more fields. Charged particles are subjected to two or more forces in a composite field, and the motion is generally complex and difficult to solve in high school. However, it is possible to design the problem of uniform motion of particles or uniform circular motion of particles.

The solution is to analyze the force and judge the unknown quantity according to the motion characteristics of the particles.

Charged particles are made in a uniform magnetic fieldUniform circumference with late filial piety movement

If the velocity direction of the charged particle is related to the magnetic induction intensity.

The direction is perpendicular and the charged particles will be subjected to the Lorentz force.

and the direction of the Lorentz force is always perpendicular to the direction of velocity, and the charged particles will move in a uniform circular motion, centripetal force.

Courtesy of Lorentz Force.

The motion of charged particles in a magnetic field.

1. Parallel magnetic field entry (V b).

The motion of the charged particles in the magnetic field enters in parallel and is not affected by the Lorentz force, and the particles move in a uniform linear motion.

2. Vertical magnetic field entry (V b).

The Lorentz force is always perpendicular to the velocity and acts as a centripetal force, moving in a uniform circular motion under the action of the Lorentz force. r=mv is obtained from qvb=mv r (centripetal force provided by the Lorentz force) and t=2 m qb or t=2 r v is obtained from qvb=m(2 t) r.

3. It is neither perpendicular nor parallel to the magnetic field.

Decompose the velocity into the direction along the magnetic field and the direction perpendicular to the magnetic field. The velocity component in the direction of the parallel magnetic field is v = v·sin, and the velocity component in the direction of the perpendicular magnetic field is v = v·cos.

The motion of charged particles in a uniform magnetic field isUniform circular motion.

When the direction of the charge velocity is delayed and perpendicular to the direction of the magnetic field, the Lorentz force.

size f=bvq; When the angle between the direction of charge motion and the direction of the magnetic field is 0, the magnitude of the Lorentz force is f=bvqsine; The most important characteristic of the Lorentz force is that the magnitude is related to the velocity.

The magnetic field has no force on the stationary charge, and the magnetic field only has an action on the moving charge, which is similar to the electric field always having an electric field force on the stationary charge or the moving charge in it.

The role is different.

The direction of the Lorentz force is always perpendicular to the direction of the velocity of the motion and can be obtained by the left-handed rule.

to judge. Charged particles act as a centripetal force under the action of the Lorentz force and can do a uniform circular motion.

General solution ideas for the motion of charged particles in a uniform magnetic field.

1. Clarify the trajectory. The motion of charged particles is a circular motion, and students need to determine the trajectory of the movement first. Some questions don't clearly tell you the trajectory, you need to analyze it yourself, draw it yourself, and sometimes you have to revise it after you draw it.

2. Find the center of the circle. After determining the approximate trajectory of motion, we began to study the center of the circle. The center of the circle is generally the perpendicular line of the velocity of two points.

Intersection. 3. Construct a suitable triangle. Combined with the subject conditions, a right-angled triangle is constructed.

and in it expresses the deflection radius r; In general, a lot of geometry knowledge is used.

4. Combined with the physical formula of the deflection radius. Once you have a radius r, combine the above physical formula R=mv bq.

The above information reference: Encyclopedia - Uniform Magnetic Field.

Uniform circular motion.

Lorentz force. It does not change the magnitude of the velocity of the charged particle, or in other words, the Lorentz force does not do work on the charged particle, and the direction of the Lorentz force is always perpendicular to the direction of velocity, which just acts as a centripetal force.

(change the direction of movement).

Extend your left hand so that your thumb is perpendicular to the remaining four fingers and all are in the same plane as your palm, allowing the magnetic lines.

Enter from the palm of your hand and point four fingers toward a positive charge.

The direction of the direction of motion, in which case the thumb is pointing is the direction of the Lorentz force on the energized wire in the magnetic field.

There are three kinds of trajectories of charged particles in a uniform magnetic field: uniform linear motion, uniform circular motion, and spiral orbital motion.

If it is a uniform magnetic field, the Lorentz force does not do work, the particle velocity remains unchanged, and the particle may move in a uniform circular motion, a uniform linear motion or a spiral motion;

If it is a uniform electric field and is subjected to a constant electric field force, according to the title, the electron is only subjected to the electric field force by one force, so the velocity of the electron cannot always be constant;

Therefore, it must enter a uniform magnetic field, and may not necessarily move in a uniform circular motion;

Therefore, choose B

Electrons that are injected into a uniform magnetic field perpendicular to the direction of the magnetic field will move in a uniform circular motion. Based on experimental phenomena, can you derive the direction of the magnetic field?

Uniform circular motion. The particle moves in a circle, and if the length of the arc is equal in the same amount of time, this motion is called "uniform circular motion", also known as "uniform circular motion". Because the velocity of the object does not change when it moves in a circle, but the direction of velocity changes when it touches the hall.

So the linear velocity of a uniform circular motion changes from moment to moment.

Calculation formula. 1. V (linear velocity) = δs δt = 2 r t = r = 2 rn (s represents arc length, t represents time, r represents radius, n represents speed).

2. (angular velocity) = δt = 2 t = 2 n (representing angle or radian) 3, t (period) = 2 r v = 2 1 n4, n ** velocity) = 1 t = v 2 r = 2 5, fn (centripetal force) = mr 2 = mv 2 r = mr4 2 t 2 = mr4 2n 2

The formula u=ed is derived from a uniform electric field. Explanation of the formula: In a uniform electric field, the potential difference between two points along the direction of the field strength is equal to the product of the field strength and the distance between these two points.

Uniform electric field: e=u is the distance between these two points along the direction of the electric field, u is the potential difference between two points in the uniform electric field, and e is the electric field strength of the uniform electric field. The difference in potential between any two points is proportional to the difference in the "displacement" of the two points in the direction of a uniform electric field.

U is the difference in electric heat, and D is naturally the displacement.

The physical significance of a uniform electric field.

The electric potential per unit length decreases along the direction of the electric field line, and the greater the voltage per unit length, the greater the field strength. This formula only applies to uniform electric fields. d in the formula refers to the projection of the distance between two points in the electric field along the direction of the electric field.

If the gravitational force of the charged particle is negligible, the particle will only be affected by the electric field force in the uniform electric field and will move at a uniform variable speed. If the gravitational force of the charged particle is not negligible, the particle may be in equilibrium under the action of two constant forces, gravity and electric field force (gravity and electric field force are balanced), or it may move at a uniform variable speed.