A bounded magnetic field problem, a physical magnetic field problem

This problem first needs to analyze the trajectory of the particle in the circular magnetic field, assuming that the particle moves in a circle along the edge of the magnetic field, according to bqv=mv 2 r, v=bqr m is obtained, and the velocity of the particle = 2bqr m, which is twice the assumption, it is not difficult to find out that the corresponding radius of motion is 2r, so the trajectory of the particle in the magnetic field is an arc with a radius of 2r, and the two ends of the arc are just the two intersection points of the arc and the edge of the magnetic field.

Okay, now determine the trajectory of the particle, down and then look at the angle from which the particle enters the magnetic field, can run in the magnetic field for the longest time, there is no doubt that if the particle in the magnetic field into and out of the two points between the arc is the longest, then his time is the longest, as we all know, if the arc on a circle is longer, it is bound to be the arc corresponding to the chord is also longer, so the first question of this question is transformed into the longest string of the magnetic field, not to mention the diameter of 2r, so the longest trajectory of the particle is to 2r as the string, 2r is the arc of the radius, as shown in the figure.

The blue one is the radius, the red one is the running trajectory, the left is clockwise, the right is counterclockwise, and the counterclockwise will not enter the electric field, so it can only be the left, and it will be shot clockwise at point A at an angle of 120 degrees with the X axis, and it will be shot at point B.

Entering the electric field, after oblique throwing motion, after falling into the x-axis, no matter what, the work done by the electric field force is only related to the vertical distance between the two points, then w=eq(rtg60+2r), e=b 2qr 2m, after substitution, w=(tg60+2)b 2qr 2 2m, and then subtract the initial kinetic energy mv0 2 2, the absolute value is, the second question is according to my analysis ideas, do it yourself.

b 2*q 2*r 2 (3 open quadratic + 5) 2m first ask the landlord if he rubs why I send a picture why can't it be displayed?

This is the physics information you found in the third year of high school, and there are questions like this!

Regardless of gravity, the particle motion is circular, and its radius is r=mv qb=so you can make the trajectory of the particle from the graph. I won't do a tula here, and then use the knowledge of analytic geometry to easily determine that the trajectory swept in the magnetic field corresponds to the radian angle of pi 3, so the running time is t=pi 3*m qb=.

I hope you can understand it, but if you can't understand it, it's because you're learning geometry too poorly. There's no way I'm going to help you face-to-face.

First of all, let me explain that today's education is not necessarily a damn education, nor is it necessarily an absolute examination-oriented education, and education is developing, and it cannot be completely denied all at once because education is insufficient, and complete denial can only do more harm than good. For example, today's human beings, if you talk about it casually, you can name many of his shortcomings, such as running as fast as animals, hearing and eyesight not as good as animals, and memory thousands of times worse than computers, etc., is it true that human beings have all kinds of shortcomings and defects and do not live, so they completely deny it? No, you can only evolve and evolve naturally.

For the bounded magnetic field, it is too practical and practical, for example, the magnetic field in the energized solenoid is approximate to the bounded uniform magnetic field, and there are many other examples, I will not give examples one by one. If there is no research on the most basic and ideal physical principles, how can there be scientific and technological achievements that advance by leaps and bounds, there will be no computers, mobile phones, and cars that you use.

I think your key question is to change the perception of science and physics.

Thinking that knowledge is useless is the reason for not learning thoroughly.

There is no true bounded magnetic field, and 90% of the approximate bounded magnetic field can be achieved through magnetic field clustering technology. High school is just solving in an ideal state, grasping the big and letting go of the small.

1. The intersection of the perpendicular line that should be the direction of incidence and the direction of emission is the center of the circle, and the direction of the incidence and exit velocity is tangent to the arc, which is equivalent to the tangent.

2. The incident point and the exit point refer to the beginning and end point of the particle's motion in the magnetic field, so it must be on the trajectory of motion. i.e. on a circular trajectory.

3. In the bounded magnetic field, if the particle is out of the magnetic field, the trajectory can only be a part of the circle, that is, a circular arc, if the particle is always moving in the magnetic field, it can also be a whole circle.

4. From 2, we can know that the incident point and the exit point are on the arc, and the connection of these two points is a string of the arc, and the perpendicular line of the string must be over the center of the circle, which is a mathematical law.

5. The period of particle motion is t, the central angle of the particle to make a full circle is 2, and the time taken is a period t, if the central angle of the arc of particle motion is t, then 2 t = t, so t = t 2.

6. The circular magnetic field has this conclusion, when entering along the radius, the perpendicular line of the line connecting the incident point and the exit point must pass the center of the circular trajectory and the center of the circular magnetic field, and then make the perpendicular line of the direction of incidence, obtain the center of the circular trajectory, connect the center of the circle to the exit point and the center of the magnetic field, and it can be known from the mathematical congruent triangle that the reverse extension line of the exit direction must be over the center of the circle.

7. The incident velocity and the exit velocity are both tangent lines of the circular trajectory, so they must be perpendicular to the radius.

8. The problem can only be established in a single-boundary magnetic field.

The CD magnetic field varies uniformly, and a constant induced current is generated in the coil, but not in the torus.

A The growth rate of magnetic field strength is weakened, the induced current in the coil is weakened, the magnetic property of the coil is weakened, according to the law of Lenda, the ABCD current is counterclockwise, the upper end of the coil is N pole, because the magnetic field of the coil is weakened before the family lift, according to Lenz's law, the magnetic field direction of the induced current in the ring is upward, so the induced current in the ring is counterclockwise, according to the left-hand rule, the ring is subjected to expansion and upward ampere force.

B The increase in the magnetic field strength increases, the induced current in the coil increases, the magnetic enhancement of the coil, according to Lenz's law, the ABCD current is counterclockwise, and the upper end of the coil is at the N pole, because the magnetic field of the coil is enhanced, according to Lenz's law, the magnetic field direction of the induced current in the ring is downward, so the induced current in the ring is clockwise, according to the left-hand rule, the ring is subject to contraction and the repulsion of the trillion downward. Choose A

Select D from the diagram to know: the current direction of the electromagnet on the line, according to the "Ampere's rule", judge that the left side of the electromagnet is the N pole, and the right side is the S pole, pay attention to the direction characteristics of the U-shaped magnet induction line!! (So the direction of the magnetic inductance line at the A end is up, the direction of the B end is down, and the middle part is horizontal" This is the key!)

The straight wire is divided into two parts, left and right, according to the left-hand rule (let the magnetic inductance line pass through the palm, the direction of the four fingers is the direction of the current, then the direction of the thumb is the direction of force at the A end; The same can be obtained at the B end) so it is determined that the ampere force on the left part of the wire at the position shown in the diagram is to the paper, and the right part is to the outside of the paper.

Take a special position: when the wire is turned 90° ("the direction of the magnetic inductance line changes to the horizontal direction"), the left-hand rule is used to judge the force (ampere force) at the midpoint of the line downward. then the wire is under the action of ampere force.

Therefore, the A end is facing the inside of the paper, and the B end is facing the outside of the paper, and the suspension tension becomes larger.

Is the left end of a straight wire in a magnetic field? What is the direction of the magnetic field?

A and B are excluded first, because E is theoretically impossible to produce without cutting the magnetic inductance lines