High school physics electromagnetism part, high school physics electromagnetism knowledge points col

1.Magnetic Induction Intensity: A physical quantity (vector quantity, unit: t) used to express the strength and direction of the magnetic field

Ampere's rule: used to determine the direction of the magnetic field or the direction of the current.

Magnetic field lines: A virtual spatial model used to describe magnetic fields.

The magnetic inductance line always starts from the n-pole and points to the s-class.

The direction of the magnetic field at a certain point is the same as the direction pointed by the n pole when the small magnetic needle is placed at that point, and if the energized wire is not affected by the magnetic field force in a certain area, the magnetic induction intensity in this area must be zero ampere force f bil(lb).

Lorentz force f qvb (vb).

The direction of both the ampere force and the Lorentz force can be determined by the left-handed rule, but the Lorentz force should pay attention to the positive and negative of the charged particles;

The induced current is conditional, the closed loop magnetic flux is changed, and the electromagnetic induction selection formula table.

Lenz's law is judged by the direction, you go she is reluctant, the magnetic flux changes fast or slow, the current is broken by it, the image problem is very typical, the direction is judged by the size, the ampere force does the work of electrical energy, and the kinetic energy theorem works.

The same start and end positions indicate that the magnetic flux changes the same, and the first and second change times indicate that the magnetic flux changes at different speeds. The first change is faster than the second, so the first time produces a greater electromotive force than the second. Therefore judge:

Option A is wrong to change the magnetic flux for the first time, because the initial position is the same as the end position, so the amount of magnetic flux change does not change.

The larger maximum declination angle of option b g indicates that the first electromotive force is relatively large, which is consistent with our reasoning, so b is right.

Option c is not true, because according to the law of conservation of energy, it can be found that the gravitational potential energy of a bar magnet is converted into electrical energy, and the energy produced by the first and second times when the initial position is the same as the final position is the same, so the work done by the electrons is the same. Thus it is judged that the lighting after g is the same.

d is wrong g does not deflect, indicating that there is no current, but the induced electromotive force is present. Think about the battery, when not in use, there is no current but there is voltage. Good luck.

D seems wrong, right? It is true that g does not deflect, but the induced electromotive force still exists, but because there is no closed loop, there is no induced current

dFalseWhen the magnetic flux passing through a closed loop changes, an induced current must be generated in the loop!

When the magnetic flux through the primary circuit changes, this circuit must produce an induced electromotive force, which is equal to the rate of change of the magnetic flux, but there is not necessarily an induced current, only when the circuit is closed, there is an induced current @

Option d should be changed to: if S is disconnected, g is not deflected, but both have induced electromotive force, and the first average induced electromotive force is equal to twice the second average induced electromotive force!

As long as the magnetic flux through a loop changes, this circuit must produce induced electromotive force A conductor cuts the magnetic inductance line motion in the magnetic field, and there is induced electromotive force at both ends of the conductor, but there is no induced current, because the circuit is not closed!

Select B to explain option D--- current can only be generated if the circuit is closed and there is an induced electromotive force. The presence of induced electromotive force is only necessary for the generation of electric current, so no induced electromotive force cannot be pushed out without an electric current.

Why is induced EMF still there? -As long as there is a change in magnetic flux in the circuit, an induced electromotive force must be generated.

m(p):m(q) 3:4,p,q are expressed as the time of motion and the electric field force exerted, and then the distance from the point of incidence to point o is expressed respectively, and two equations appear to make them equal.

I haven't done the question for a long time, if it's wrong, bear with me!!

The particle moves like a flat throw in an electric field, which is caused by x=vt; y = at available:

a = 2yv² /x² ①

and a = qe m

Substituting m yields: m = qex 2yv i.e. m qx

So m p mq = 3 4

The correct answer to this question should be option C, we set the three balls as ball A ball B and ball C respectively, the charge amount of ball A is +q, the charge amount of ball B is -q, and the charge amount of ball C is 0, if the C ball is in contact with ball A, then the two balls are divided into +Q 2, and if the C ball with +Q 2 is in contact with the B ball with the charge of -q, then +Q 2 and -Q 2 are eliminated first, and then the remaining -Q 2 of ball B is divided equally among ball C, then both ball B and ball C have -Q 4, bringing the existing charge amount of ball A and ball B into f=kq1q2 r 2, find f1, and then f1 f, the result is equal to 1 8, so it is f 8

The friend who chose the D option did not take into account that the A ball and the B ball were heterogeneous charges, so they calculated 3f 8

But the correct answer should be option C. Thank you.

c The original two small balls have a different charge, and after the third ball is contacted, the original two small balls have a charge of q 2 and q 4, f = kq1q2 r 2, so the force is the original 1 8

The answer is d.

Solution: The charge will be distributed evenly after the contact of the dotted ball, let the original charge be q, when the third uncharged ball contacts the charged ball for the first time, the charge is distributed, both are 1 2q, when the third ball contacts the dotted ball for the second time, it is distributed again, (1 2q+q) 2=3 4q, and then by the formula: f=(k*q*q) (r*r), then the attraction between the two balls after the charge contacts f2=(k*1 2q*3 4q) (r*r)=3 8f

The title says that "mutual attraction" has a different charge, assuming that at first ball A is not charged with +q, B with -q, and C is not charged. After contact between A and C, the first band is +q 2, and the C band is +q 2;C is then in contact with B, and B is band (-q+q 2) 2=-q 4. It can be seen that the mutual attraction becomes f 8. Choose C

Find out all the definitions from the book yourself.

Transcribe it carefully.